💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc5978.txt captured on 2023-01-29 at 05:37:05.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Internet Engineering Task Force (IETF) J. Manner
Request for Comments: 5978 Aalto University
Category: Informational R. Bless
ISSN: 2070-1721 KIT
J. Loughney
Nokia
E. Davies, Ed.
Folly Consulting
October 2010
Using and Extending the NSIS Protocol Family
Abstract
This document gives an overview of the Next Steps in Signaling (NSIS)
framework and protocol suite created by the NSIS Working Group during
the period of 2001-2010. It also includes suggestions on how the
industry can make use of the new protocols and how the community can
exploit the extensibility of both the framework and existing
protocols to address future signaling needs.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5978.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
Manner, et al. Informational [Page 1]
RFC 5978 NSIS User and Extension Guide October 2010
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. The NSIS Architecture . . . . . . . . . . . . . . . . . . . . 3
3. The General Internet Signaling Transport . . . . . . . . . . . 6
4. Quality-of-Service NSLP . . . . . . . . . . . . . . . . . . . 11
5. NAT/Firewall Traversal NSLP . . . . . . . . . . . . . . . . . 12
6. Deploying the Protocols . . . . . . . . . . . . . . . . . . . 13
6.1. Deployment Issues Due to Use of RAO . . . . . . . . . . . 14
6.2. Deployment Issues with NATs and Firewalls . . . . . . . . 15
6.3. Incremental Deployment and Workarounds . . . . . . . . . . 15
7. Security Features . . . . . . . . . . . . . . . . . . . . . . 16
8. Extending the Protocols . . . . . . . . . . . . . . . . . . . 16
8.1. Overview of Administrative Actions Needed When
Extending NSIS . . . . . . . . . . . . . . . . . . . . . . 17
8.2. GIST . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2.1. Use of Different Message Routing Methods . . . . . . . 18
8.2.2. Use of Different Transport Protocols or Security
Capabilities . . . . . . . . . . . . . . . . . . . . . 18
8.2.3. Use of Alternative Security Services . . . . . . . . . 19
8.2.4. Query Mode Packet Interception Schemes . . . . . . . . 19
8.2.5. Use of Alternative NAT Traversal Mechanisms . . . . . 20
8.2.6. Additional Error Identifiers . . . . . . . . . . . . . 20
8.2.7. Defining New Objects To Be Carried in GIST . . . . . . 21
8.2.8. Adding New Message Types . . . . . . . . . . . . . . . 21
8.3. QoS NSLP . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.4. QoS Specifications . . . . . . . . . . . . . . . . . . . . 22
8.5. NAT/Firewall NSLP . . . . . . . . . . . . . . . . . . . . 23
8.6. New NSLP Protocols . . . . . . . . . . . . . . . . . . . . 23
9. Security Considerations . . . . . . . . . . . . . . . . . . . 26
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
11.1. Normative References . . . . . . . . . . . . . . . . . . . 27
11.2. Informative References . . . . . . . . . . . . . . . . . . 28
Manner, et al. Informational [Page 2]
RFC 5978 NSIS User and Extension Guide October 2010
1. Introduction
The Next Steps in Signaling (NSIS) Working Group was formed in
November 2001 to develop an Internet signaling protocol suite that
would attempt to remedy some of the perceived shortcomings of
solutions based on the Resource ReSerVation Protocol (RSVP), e.g.,
with respect to mobility and Quality-of-Service (QoS)
interoperability. The initial charter was focused on QoS signaling
as the first use case, taking RSVP as the background for the work.
In May 2003, middlebox traversal was added as an explicit second use
case. The requirements for the new generation of signaling protocols
are documented in [RFC3726], and an analysis of existing signaling
protocols can be found in [RFC4094].
The design of NSIS is based on a two-layer model, where a general
signaling transport layer provides services to an upper signaling
application layer. The design was influenced by Bob Braden's
document entitled "A Two-Level Architecture for Internet Signaling"
[TWO-LEVEL].
This document gives an overview of the NSIS framework and protocol
suite at the time of writing (2010), provides an introduction to the
use cases for which the current version of NSIS was designed,
describes how to deploy NSIS in existing networks, and summarizes how
the protocol suite can be enhanced to satisfy new use cases.
2. The NSIS Architecture
The design of the NSIS protocol suite reuses ideas and concepts from
RSVP but essentially divides the functionality into two layers. The
lower layer, the NSIS Transport Layer Protocol (NTLP), is in charge
of transporting the higher-layer protocol messages to the next
signaling node on the path. This includes discovery of the next-hop
NSIS node, which may not be the next routing hop, and different
transport and security services depending on the signaling
application requirements. The General Internet Signaling Transport
(GIST) [RFC5971] has been developed as the protocol that fulfills the
role of the NTLP. The NSIS protocol suite supports both IP protocol
versions, IPv4 and IPv6.
The actual signaling application logic is implemented in the higher
layer of the NSIS stack, the NSIS Signaling Layer Protocol (NSLP).
While GIST is only concerned with transporting NSLP messages hop-by-
hop between pairs of signaling nodes, the end-to-end signaling
functionality is provided by the NSLP protocols if needed. Not all
NSLP protocols need to perform end-to-end signaling. The current
protocols have features to confine the signaling to a limited part of
the path (such as the interior of a domain). Messages transmitted by
Manner, et al. Informational [Page 3]
RFC 5978 NSIS User and Extension Guide October 2010
GIST on behalf of an NSLP are identified by a unique NSLP identifier
(NSLPID) associated with the NSLP. Two NSLP protocols are currently
specified: one concerning Quality-of-Service signaling [RFC5974] and
one to enable NAT/firewall traversal [RFC5973].
NSIS is primarily designed to provide the signaling needed to install
state on nodes that lie on the path that will be taken by some end-
to-end flow of data packets; the state installed should facilitate or
enhance some characteristic of the data flow. This is typically
achieved by routing signaling messages along the same path (known as
"path-coupled signaling") and intercepting the signaling message at
NSIS-capable nodes. However, the NSIS architecture is designed to be
flexible, and the routing of signaling messages is controlled by the
Message Routing Method (MRM) that is applied to the signaling
messages. The initial specifications define two MRMs:
o the basic Path Coupled MRM designed to drive signaling along the
path that will be followed by the data flow, and
o an alternative Loose End MRM, which is applicable for
preconditioning the state in firewalls and Network Address
Translation (NAT) middleboxes when data flow destinations lie
behind this sort of middlebox. Without preconditioning, these
middleboxes will generally reject signaling messages originating
outside the region 'protected' by the middlebox and where the
destination is located.
Parameters carried by each signaling message drive the operation of
the relevant transport or signaling application. In particular, the
messages will carry Message Routing Information (MRI) that will allow
the NSIS nodes to identify the data flow to which the signaling
applies. Generally, the intercepted messages will be reinjected into
the network after processing by the NSIS entities and will be routed
further towards the destination, possibly being intercepted by
additional NSIS-capable nodes before arriving at the flow endpoint.
As with RSVP, it is expected that the signaling message will make a
complete round trip either along the whole end-to-end path or a part
of it if the scope of the signaling is limited. This implements a
two-phase strategy in which capabilities are assessed and provisional
reservations are made on the outbound leg; these provisional
reservations are then confirmed and operational state is installed on
the return leg. Unlike RSVP, signaling is normally initiated at the
source of the data flow, making it easier to ensure that the
signaling follows the expected path of the data flow, but can also be
receiver initiated as in RSVP.
Manner, et al. Informational [Page 4]
RFC 5978 NSIS User and Extension Guide October 2010
A central concept of NSIS is the Session Identifier (SID). Signaling
application states are indexed and referred to through the SID in all
the NSLPs. This decouples the state information from IP addresses,
allowing dynamic IP address changes for signaling flows, e.g., due to
mobility: changes in IP addresses do not force complete teardown and
re-initiation of a signaling application state; they force merely an
update of the state parameters in the NSLP(s), especially the MRI.
At the NTLP (GIST) layer, the SID is not meaningful by itself, but is
used together with the NSLP identifier (NSLPID) and the Message
Routing Information (MRI). This 3-tuple is used by GIST to index and
manage the signaling flows. Changes of routing or dynamic IP address
changes, e.g., due to mobility, will require GIST to modify already
established Messaging Associations (MAs) that are used to channel
NSLP messages between adjacent GIST peers in order to satisfy the
NSLP MRI for each SID.
The following design restrictions were imposed for the first phase of
the protocol suite. They may be lifted in the future, and new
functionality may be added into the protocols at some later stage.
o Initial focus on MRMs for path-coupled signaling: GIST transports
messages towards an identified unicast data flow destination based
on the signaling application request, and does not directly
support path-decoupled signaling, e.g., QoS signaling to a
bandwidth broker or other off-path resource manager. The
framework also supports a Loose End MRM used to discover GIST
nodes with particular properties in the direction of a given
address; for example, the NAT/firewall NSLP uses this method to
discover a NAT along the upstream data path.
o No multicast support: Introducing support for multicast was deemed
too much overhead, considering the currently limited support for
global IP multicast. Thus, the current GIST and the NSLP
specifications consider unicast flows only.
The key documents specifying the NSIS framework are:
o Requirements for Signaling Protocols [RFC3726]
o Next Steps in Signaling: Framework [RFC4080]
o Security Threats for NSIS [RFC4081]
The protocols making up the suite specified by the NSIS Working Group
are documented in:
o The General Internet Signaling Transport protocol [RFC5971]
Manner, et al. Informational [Page 5]
RFC 5978 NSIS User and Extension Guide October 2010
o Quality-of-Service NSLP (QoS NSLP) [RFC5974]
o The QoS specification template [RFC5975]
o NAT/firewall traversal NSLP [RFC5973]
The next three sections provide a brief survey of GIST, the QoS NSLP,
and the NAT/firewall NSLP.
3. The General Internet Signaling Transport
The General Internet Signaling Transport (GIST) [RFC5971] provides
signaling transport and security services to NSIS Signaling Layer
Protocols (NSLP) and the associated signaling applications. GIST
does not define new IP transport protocols or security mechanisms but
rather makes use of existing protocols, such as TCP, UDP, TLS, and
IPsec. Applications can indicate the desired transport attributes
for the signaling flow, e.g., unreliable or reliable, and GIST then
chooses the most appropriate transport protocol(s) to satisfy the
requirements of the flow. GIST will normally use UDP if unreliable
signaling is adequate, TCP if reliability is required, and TLS over
TCP for secure (and reliable) signaling flows, but there exist
extensibility provisions within GIST that will allow alternatives to
be specified in the future. The NSIS layered protocol stack is shown
in Figure 1.
Manner, et al. Informational [Page 6]
RFC 5978 NSIS User and Extension Guide October 2010
+-----+ +--------+ +-------+
| | | | | |
| QoS | | NAT/FW | | ... | NSLP
| | | | | |
+-----+ +--------+ +-------+
---------------------------------------------------------------------
+--------------------------+
| |
| GIST | NTLP
| |
+--------------------------+
---------------------------------------------------------------------
+------------+-------------+
| TLS | DTLS | Security Support*
+------------+-------------+
| TCP | SCTP | UDP | DCCP | Transport Protocol*
+--------------------------+
+--------------------------+
| IPsec |
+--------------------------+
+--------------------------+
| IPv4 | IPv6 |
+--------------------------+
* The Security Support and Transport Protocol layers show some
possible protocols that could be used to transport NSIS messages.
To provide authentication and/or integrity protection support,
the transport protocol has to be paired with a suitable security
mechanism, e.g., TCP with TLS, or Datagram Congestion Control
Protocol (DCCP) with DTLS.
Figure 1: The NSIS protocol stack
GIST divides up the data flow's end-to-end path into a number of
segments between pairs of NSIS-aware peer nodes located along the
path. Not every router or other middlebox on the path needs to be
NSIS aware: each segment of the signaling path may incorporate
several routing hops. Also not every NSIS-aware node necessarily
implements every possible signaling application. If the signaling
for a flow requests services from a subset of the applications, then
only nodes that implement those services are expected to participate
as peers, and even some of these nodes can decline to operate on a
particular flow if, for example, the additional load might overload
the processing capability of the node. These characteristics mean
that incremental deployment of NSIS capabilities is possible both
with the initial protocol suite, and for any future NSLP applications
Manner, et al. Informational [Page 7]
RFC 5978 NSIS User and Extension Guide October 2010
that might be developed. The following paragraphs describe how a
signaling segment is set up to offer the transport and security
characteristics needed by a single NSLP.
When an NSLP application wants to send a message towards a flow
endpoint, GIST starts the process of discovering the next signaling
node by sending a Query message towards the destination of the
related data flow. This Query carries the NSLP identifier (NSLPID)
and Message Routing Information (MRI), among others. The MRI
contains enough information to control the routing of the signaling
message and to identify the associated data flow. The next GIST node
on the path receives the message, and if it is running the same NSLP,
it provides the MRI to the NSLP application and requests it to make a
decision on whether to peer with the querying node. If the NSLP
application chooses to peer, GIST sets up a Message Routing State
(MRS) between the two nodes for the future exchange of NSLP data.
State setup is performed by a three-way handshake that allows for
negotiation of signaling flow parameters and provides counter-
measures against several attacks (like denial-of-service) by using
cookie mechanisms and a late state installation option.
If a transport connection is required and needs to provide for
reliable or secure signaling, like TCP or TLS/TCP, a Messaging
Association (MA) is established between the two peers. An MA can be
reused for signaling messages concerning several different data
flows, i.e., signaling messages between two nodes are multiplexed
over the same transport connection. This can be done when the
transport requirements (reliability, security) of a new flow can be
met with an existing MA, i.e., the security and transport properties
of an existing MA are equivalent or better than what is requested for
a potential new MA.
For path-coupled signaling, we need to find the nodes on the data
path that should take part in the signaling of an NSLP and invoke
them to act on the arrival of such NSLP signaling messages. The
basic concept is that such nodes along a flow's data path intercept
the corresponding signaling packets and are thus discovered
automatically. GIST places a Router Alert Option (RAO) in Query
message packets to ensure that they are intercepted by relevant NSIS-
aware nodes, as in RSVP.
Late in the development of GIST, serious concerns were raised in the
IETF about the security risks and performance implications of
extensive usage of the RAO [RAO-BAD]. Additionally, evidence was
discovered indicating that several existing implementations of RAO
were inconsistent with the (intention of the) standards and would not
support the NSIS usage. There were also concerns that extending the
need for RAO recognition in the fast path of routers that are
Manner, et al. Informational [Page 8]
RFC 5978 NSIS User and Extension Guide October 2010
frequently implemented in hardware would delay or deter
implementation and deployment of NSIS. Eventually, it was decided
that NSIS would continue to specify RAO as its primary means for
triggering interception of signaling messages in intermediate nodes
on the data path, but the protocol suite would be published with
Experimental status rather than on the Standards Track while
deployment experience was gathered. More information about the use
of RAO in GIST can be found in [GIST-RAO]. Also, the deployment
issues that arise from the use of RAO are discussed in Section 6.1.
Alternative mechanisms have been considered to allow nodes to
recognize NSIS signaling packets that should be intercepted. For
example, NSIS nodes could recognize UDP packets directed to a
specific destination port as Query messages that need to be
intercepted even though they are not addressed to the intercepting
node. GIST provides for the use of such alternatives as a part of
its extensibility design. NSIS recognizes that the workload imposed
by intercepting signaling packets could be considerable relative to
the work needed just to forward such packets. To keep the necessary
load to a minimum, NSIS provides mechanisms to limit the number of
interceptions needed by constraining the rate of generation and
allowing for intentional bypassing of signaling nodes that are not
affected by particular signaling requests. This can be accomplished
either in GIST or in the NSLP.
Since GIST carries information about the data flow inside its
messages (in the MRI), NAT gateways must be aware of GIST in order to
let it work correctly. GIST provides a special object for NAT
traversal so that the actual translation is disclosed if a GIST-aware
NAT gateway provides this object.
As with RSVP, all the state installed by NSIS protocols is "soft-
state" that will expire and be automatically removed unless it is
periodically refreshed. NSIS state is held both at the signaling
application layer and in the signaling transport layer, and is
maintained separately. NSLPs control the lifetime of the state in
the signaling application layer by setting a timeout and sending
periodic "keep alive" messages along the signaling path if no other
messages are required. The MAs and the routing state are maintained
semi-independently by the transport layer, because MAs may be used by
multiple NSLP sessions, and can also be recreated "on demand" if the
node needs to reclaim resources. The transport layer can send its
own "keep alive" messages across a MA if no NSLP messages have been
sent, for example, if the transport layer decides to maintain a
heavily used MA even though there is no current NSLP session using
it. Local state can also be deleted explicitly when no longer
needed.
Manner, et al. Informational [Page 9]
RFC 5978 NSIS User and Extension Guide October 2010
If there is a change in the route used by a flow for which NSIS has
created state, NSIS needs to detect the change in order to determine
if the new path contains additional NSIS nodes that should have state
installed. GIST may use a range of triggers in order to detect a
route change. It probes periodically for the next peer by sending a
GIST Query, thereby detecting a changed route and GIST peer. GIST
monitors routing tables and the GIST peer states, and it notifies
NSLPs of any routing changes. It is then up to the NSLPs to act
appropriately, if needed, e.g., by issuing a refresh message. The
periodic queries also serve to maintain the soft-state in nodes as
long as the route is unchanged.
In summary, GIST provides several services in one package to the
upper-layer signaling protocols:
o Signaling peer discovery: GIST is able to find the next-hop node
that runs the NSLP being signaled for.
o Multiplexing: GIST reuses already established signaling
relationships and messaging associations to next-hop peers if the
signaling flows require the same transport attributes.
o Transport: GIST provides transport with different attributes --
namely, reliable/unreliable and secure/unsecure.
o Security: If security is requested, GIST uses TLS to provide an
encrypted and integrity-protected message transport to the next
signaling peer.
o Routing changes: GIST detects routing changes, but instead of
acting on its own, it merely sends a notification to the local
NSLP. It is then up to the NSLP to act.
o Fragmentation: GIST uses either a known Path MTU for the next hop
or limits its message size to 576 bytes when using UDP or Query
mode. If fragmentation is required, it automatically establishes
an MA and sends the signaling traffic over a reliable protocol,
e.g., TCP.
o State maintenance: GIST establishes and then maintains the soft-
state that controls communications through MAs between GIST peers
along the signaling path, according to usage parameters supplied
by NSLPs and local policies.
Manner, et al. Informational [Page 10]
RFC 5978 NSIS User and Extension Guide October 2010
4. Quality-of-Service NSLP
The Quality-of-Service (QoS) NSIS Signaling Layer Protocol (NSLP)
establishes and maintains state at nodes along the path of a data
flow for the purpose of providing some forwarding resources for that
flow. It is intended to satisfy the QoS-related requirements of RFC
3726 [RFC3726]. No support for QoS architectures based on bandwidth
brokers or other off-path resource managers is currently included.
The design of the QoS NSLP is conceptually similar to RSVP, RFC 2205
[RFC2205], and uses soft-state peer-to-peer refresh messages as the
primary state management mechanism (i.e., state installation/refresh
is performed between pairs of adjacent NSLP nodes, rather than in an
end-to-end fashion along the complete signaling path). The QoS NSLP
extends the set of reservation mechanisms to meet the requirements of
RFC 3726 [RFC3726], in particular, support of sender- or receiver-
initiated reservations, as well as, a type of bidirectional
reservation and support of reservations between arbitrary nodes,
e.g., edge-to-edge, end-to-access, etc. On the other hand, there is
currently no support for IP multicast.
A distinction is made between the operation of the signaling protocol
and the information required for the operation of the Resource
Management Function (RMF). RMF-related information is carried in the
QSPEC (QoS Specification) object in QoS NSLP messages. This is
similar to the decoupling between RSVP and the IntServ architecture,
RFC 1633 [RFC1633]. The QSPEC carries information on resources
available, resources required, traffic descriptions, and other
information required by the RMF. A template for QSPEC objects is
defined in [RFC5975]. This provides a number of basic parameter
objects that can be used as a common language to specify components
of concrete QoS models. The objects defined in [RFC5975] provide the
building blocks for many existing QoS models such as those associated
with RSVP and Differentiated Services. The extensibility of the
template allows new QoS model specifications to extend the template
language as necessary to support these specifications.
The QoS NSLP supports different QoS models because it does not define
the QoS mechanisms and RMF that have to be used in a domain. As long
as a domain knows how to perform admission control for a given QSPEC,
QoS NSLP actually does not care how the specified constraints are
enforced and met, e.g., by putting the related data flow in the
topmost of four Diffserv classes or by putting it into the third
highest of twelve Diffserv classes. The particular QoS configuration
used is up to the network provider of the domain. The QSPEC can be
seen as a common language to express QoS requirements between
different domains and QoS models.
Manner, et al. Informational [Page 11]
RFC 5978 NSIS User and Extension Guide October 2010
In short, the functionality of the QoS NSLP includes:
o Conveying resource requests for unicast flows
o Resource requests (QSPEC) that are decoupled from the signaling
protocol (QoS NSLP)
o Sender- and receiver-initiated reservations, as well as
bidirectional
o Soft-state and reduced refresh (keep-alive) signaling
o Session binding, i.e., session X can be valid only if session Y is
also valid
o Message scoping, end-to-end, edge-to-edge, or end-to-edge (proxy
mode)
o Protection against message re-ordering and duplication
o Group tear, tearing down several sessions with a single message
o Support for rerouting, e.g., due to mobility
o Support for request priorities and preemption
o Stateful and stateless nodes: stateless operation is particularly
relevant in core networks where large amounts of QoS state could
easily overwhelm a node
o Reservation aggregation
The protocol also provides for a proxy mode to allow the QoS
signaling to be implemented without needing all end-hosts to be
capable of handling NSIS signaling.
The QSPEC template supports situations where the QoS parameters need
to be fine-grained, specifically targeted to an individual flow in
one part of the network (typically the edge or access part) but might
need to be more coarse-grained, where the flow is part of an
aggregate (typically in the core of the network).
5. NAT/Firewall Traversal NSLP
The NAT/firewall traversal NSLP [RFC5973] lets end-hosts interact
with NAT and firewall devices in the data path. Basically, it allows
for a dynamic configuration of NATs and/or firewalls along the data
path in order to enable data flows to traverse these devices without
Manner, et al. Informational [Page 12]
RFC 5978 NSIS User and Extension Guide October 2010
being obstructed. For instance, firewall pinholes could be opened on
demand by authorized hosts. Furthermore, it is possible to block
unwanted incoming traffic on demand, e.g., if an end-host is under
attack.
Configurations to be implemented in NAT and firewall devices signaled
by the NAT/firewall NSLP take the form of a (pattern, action) pair,
where the pattern specifies a template for packet header fields to be
matched. The device is then expected to apply the specified action
to any passing packet that matches the template. Actions are
currently limited to ALLOW (forward the packet) and DENY (drop the
packet). The template specification allows for a greater range of
packet fields to be matched than those allowed for in the GIST MRI.
Basically, NAT/firewall signaling starts at the data sender (NSIS
Initiator) before any actual application data packets are sent.
Signaling messages may pass several middleboxes that are NAT/firewall
NSLP aware (NSIS Forwarder) on their way downstream and usually hit
the receiver (being the NSIS Responder). A proxy mode is also
available for cases where the NAT/firewall NSLP is not fully
supported along the complete data path. NAT/firewall NSLP is based
on a soft-state concept, i.e., the sender must periodically repeat
its request in order to keep it active.
Additionally, the protocol also provides functions for receivers
behind NATs. The receiver may request an external address that is
reachable from outside. The reserved external address must, however,
be communicated to the sender out-of-band by other means, e.g., by
application level signaling. After this step the data sender may
initiate a normal NAT/firewall signaling in order to create firewall
pinholes.
The protocol also provides for a proxy mode to allow the NAT/firewall
signaling to be implemented without needing all end-hosts to be
capable of handling NSIS signaling.
6. Deploying the Protocols
The initial version of the NSIS protocol suite is being published
with the status of Experimental in order to gain deployment
experience. Concerns over the security, implementation, and
administrative issues surrounding the use of RAO are likely to mean
that initial deployments occur in "walled gardens" where the
characteristics of hardware in use are well-known, and there is a
high level of trust and control over the end nodes that use the
protocols. This section addresses issues that need to be considered
in a deployment of the NSIS protocol suite.
Manner, et al. Informational [Page 13]
RFC 5978 NSIS User and Extension Guide October 2010
First of all, NSIS implementations must be available in at least some
of the corresponding network nodes (i.e., routers, firewalls, or NAT
gateways) and end-hosts. That means not only GIST support, but also
the NSLPs and their respective control functions (such as a resource
management function for QoS admission control, etc.) must be
implemented. NSIS is capable of incremental deployment and an
initial deployment does not need to involve every node in a network
domain. This is discussed further in Section 6.3. There are a
number of obstacles that may be encountered due to broken
implementations of RAO (see Section 6.1) and due to firewalls or NATs
that drop NSIS signaling packets (see Section 6.2).
Another important issue is that applications may need to be made
NSIS-aware, thereby requiring some effort from the applications'
programmers. Alternatively, it may be possible to implement separate
applications to control, e.g., the network QoS requests or firewall
pinholes, without needing to update the actual applications that will
take advantage of NSIS capabilities.
6.1. Deployment Issues Due to Use of RAO
The standardized version of GIST depends on routers and other
middleboxes correctly recognizing and acting on packets containing
RAO. There are a number of problems related to RAO that can obstruct
a deployment of NSIS:
o Some implementations do not respond to RAO at all.
o Some implementations respond but do not distinguish between the
RAO parameter values in IPv4 packets or reject anything except 0
(in which case, only the value 0 can be used).
o The response to RAO in a GIST Query mode packet, which is sent
using the UDP transport, is to dispatch the packet to the UDP
stack in the intercepting node rather than to a function
associated with the RAO parameter. Since the node will not
normally have a regular UDP receiver for these packets they are
dropped.
o The major security concern with RAO in NSIS is that it provides a
new vector for hosts to mount a (distributed) denial-of-service
(DDoS) attack on the control plane of routers on the data path.
Such attacks have occurred, and it is therefore normal for service
providers to prohibit "host-to-router" signaling packets such as
RSVP or NSIS from entering their networks from customer networks.
This will tend to limit the deployment of NSIS to "walled gardens"
unless a suitable mitigation of the DDoS threat can be found and
deployed.
Manner, et al. Informational [Page 14]
RFC 5978 NSIS User and Extension Guide October 2010
In order to deploy NSIS effectively, routers and other hardware need
to be selected and correctly configured to respond to RAO and
dispatch intercepted packets to the NSIS function.
A further obstacle results from the likelihood that IPv4 packets with
IP options of any kind will be filtered and dropped by firewalls and
NATs. In many cases, this is the default behavior so that explicit
configuration is needed to allow packets carrying the RAO to pass
through. The general inclination of domain administrators is to deny
access to packets carrying IP options because of the security risks
and the additional load on the routers in the domain. The situation
with IPv6 may be easier, as the RAO option in IPv6 is better defined,
but the security concerns remain.
Deployment issues are discussed at more length in Appendix C of the
GIST specification [RFC5971].
6.2. Deployment Issues with NATs and Firewalls
NAT gateways and firewalls may also hinder initial deployment of NSIS
protocols for several reasons:
o They may filter and drop signaling traffic (as described in
Section 6.1) to deny access to packets containing IP options.
o They may not permit "unsolicited" incoming GIST Query mode
packets. This behavior has been anticipated in the design of the
protocols but requires additional support to ensure that the
middleboxes are primed to accept the incoming queries (see
[RFC5974] and [RFC5973]).
o NATs that are not aware of the NSIS protocols will generally
perform address translations that are not coordinated with the
NSIS protocols. Since NSIS signaling messages may be carrying
embedded IP addresses affected by these translations, it may not
be possible to operate NSIS through such legacy NATs. The
situation and workarounds are discussed in Section 7.2.1 of
[RFC5971].
6.3. Incremental Deployment and Workarounds
NSIS is specifically designed to be incrementally deployable. It is
not required that all nodes on the signaling and data path are NSIS
aware. To make any use of NSIS, at least two nodes on the path need
to be NSIS aware. However, it is not essential that the initiator
and receiver of the data flow are NSIS aware. Both the QoS and NAT/
firewall NSLPs provide "proxy modes" in which nodes adjacent to the
initiator and/or receiver can act as proxy signaling initiator or
Manner, et al. Informational [Page 15]
RFC 5978 NSIS User and Extension Guide October 2010
receiver. An initiator proxy can monitor traffic and, hopefully,
detect when a data flow of a type needing NSIS support is being
initiated. The proxies can act more or less transparently on behalf
of the data flow initiator and/or receiver to set up the required
NSIS state and maintain it while the data flow continues. This
capability reduces the immediate need to modify all the data flow
endpoints before NSIS is viable.
7. Security Features
Basic security functions are provided at the GIST layer, e.g.,
protection against some blind or denial-of-service attacks, but note
that introduction of alternative MRMs may provide attack avenues that
are not present with the current emphasis on the path-coupled MRM.
Conceptually, it is difficult to protect against an on-path attacker
and man-in-the-middle attacks when using path-coupled MRMs, because a
basic functionality of GIST is to discover as yet unknown signaling
peers. Transport security can be requested by signaling applications
and is realized by using TLS between signaling peers, i.e.,
authenticity and confidentiality of signaling messages can be assured
between peers. GIST allows for mutual authentication of the
signaling peers (using TLS means such as certificates) and can verify
the authenticated identity against a database of nodes authorized to
take part in GIST signaling. It is, however, a matter of policy that
the identity of peers is verified and accepted upon establishment of
the secure TLS connection.
While GIST is handling authentication of peer nodes, more fine-
grained authorization may be required in the NSLP protocols. There
is currently an ongoing work to specify common authorization
mechanisms to be used in NSLP protocols [NSIS-AUTH], thus allowing,
e.g., per-user and per-service authorization.
8. Extending the Protocols
This section discusses the ways that are available to extend the NSIS
protocol suite. The Next Steps in Signaling (NSIS) Framework
[RFC4080] describes a two-layer framework for signaling on the
Internet, comprising a generic transport layer with specific
signaling-layer protocols to address particular applications running
over this transport layer. The model is designed to be highly
extensible so that it can be adapted for different signaling needs.
It is expected that additional signaling requirements will be
identified in the future. The two-layer approach allows for NSLP
signaling applications to be developed independently of the transport
protocol. Further NSLPs can therefore be developed and deployed to
meet these new needs using the same GIST infrastructure, thereby
Manner, et al. Informational [Page 16]
RFC 5978 NSIS User and Extension Guide October 2010
providing a level of macro-extensibility. However, the GIST protocol
and the two signaling applications have been designed so that
additional capabilities can be incorporated into the design should
additional requirements within the general scope of these protocols
need to be accommodated.
The NSIS framework is also highly supportive of incremental
deployment. A new NSLP need not be available on every NSIS-aware
node in a network or along a signaling path in order to start using
it. Nodes that do not (yet) support the application will forward its
signaling messages without complaint until it reaches a node where
the new NSLP application is deployed.
One key functionality of parameter objects carried in NSIS protocols
is the so-called "Extensibility flags (A/B)". All the existing
protocols (and any future ones conforming to the standards) can carry
new experimental objects, where the A/B flags can indicate whether a
receiving node must interpret the object, or whether it can just drop
them or pass them along in subsequent messages sent out further on
the path. This functionality allows defining new objects without
forcing all network entities to understand them.
8.1. Overview of Administrative Actions Needed When Extending NSIS
Generally, NSIS protocols can be extended in multiple ways, many of
which require the allocation of unique code point values in
registries maintained by IANA on behalf of the IETF. This and the
following sections provide an overview of the administrative
mechanisms that might apply. The extensibility rules defined below
are based upon the procedures by which IANA assigns values: "IESG
Approval", "IETF Review", "Expert Review", and "Private Use" (as
specified in [RFC5226]). The appropriate procedure for a particular
type of code point is defined in one or other of the NSIS protocol
documents, mostly [RFC5971].
In addition to registered code points, all NSIS protocols provide
code points that can be used for experimentation, usually within
closed networks, as explained in [RFC3692]. There is no guarantee
that independent experiments will not be using the same code point!
8.2. GIST
GIST is extensible in several aspects covered in the subsections
below. In these subsections, there are references to document
sections in the GIST specification [RFC5971] where more information
can be found. The bullet points at the end of each subsection
specify the formal administrative actions that would need to be
carried out when a new extension is standardized.
Manner, et al. Informational [Page 17]
RFC 5978 NSIS User and Extension Guide October 2010
More generally, as asserted in Section 1 of the GIST specification,
the GIST design could be extended to cater for multicast flows and
for situations where the signaling is not tied to an end-to-end data
flow. However, it is not clear whether this could be done in a
totally backwards-compatible way, and this is not considered within
the extensibility model of NSIS.
8.2.1. Use of Different Message Routing Methods
Currently, only two message routing methods are supported (Path
Coupled MRM and Loose End MRM), but further MRMs may be defined in
the future. See Sections 3.3 and 5.8 of the GIST specification
[RFC5971]. One possible additional MRM under development is
documented in [EST-MRM]. This MRM would direct signaling towards an
explicit target address other than the (current) data flow
destination and is intended to assist setting up of state on a new
path during "make-before-break" handover sequences in mobile
operations. Note that alternative routing methods may require
modifications to the firewall traversal techniques used by GIST and
NSLPs.
o New MRMs require allocation of a new MRM-ID either by IETF review
of a specification or expert review [RFC5971].
8.2.2. Use of Different Transport Protocols or Security Capabilities
The initial handshake between GIST peers allows a negotiation of the
transport protocols to be used. Currently, proposals exist to add
DCCP [GIST-DCCP] and the Stream Control Transmission Protocol (SCTP)
[GIST-SCTP] transports to GIST; in each case, using Datagram TLS
(DTLS) to provide security. See Sections 3.2 and 5.7 of the GIST
specification [RFC5971]. GIST expects alternative capabilities to be
treated as selection of an alternative protocol stack. Within the
protocol stack, the individual protocols used are specified by MA
Protocol IDs that are allocated from an IANA registry if new
protocols are to be used. See Sections 5.7 and 9 of the GIST
specification [RFC5971].
o Use of an alternative transport protocol or security capability
requires allocation of a new MA-Protocol-ID either by IETF review
of a specification or expert review [RFC5971].
Manner, et al. Informational [Page 18]
RFC 5978 NSIS User and Extension Guide October 2010
8.2.3. Use of Alternative Security Services
Currently, only TLS is specified for providing secure channels with
MAs. Section 3.9 of the GIST specification [RFC5971] suggests that
alternative protocols could be used, but the interactions with GIST
functions would need to be carefully specified. See also Section
4.4.2 of the GIST specification [RFC5971].
o Use of an alternative security service requires allocation of a
new MA-Protocol-ID either by IETF review of a specification or
expert review [RFC5971].
8.2.4. Query Mode Packet Interception Schemes
GIST has standardized a scheme using RAO mechanisms [GIST-RAO] with
UDP packets. If the difficulties of deploying the RAO scheme prove
insuperable in particular circumstances, alternative interception
schemes can be specified. One proposal that was explored for GIST
used UDP port recognition in routers (rather than RAO mechanisms) to
drive the interception of packets. See Section 5.3.2 of the GIST
specification [RFC5971]. Each NSLP needs to specify membership of an
"interception class" whenever it sends a message through GIST. A
packet interception scheme can support one or more interception
classes. In principle, a GIST instance can support multiple packet
interception schemes, but each interception class needs to be
associated with exactly one interception scheme in a GIST instance,
and GIST instances that use different packet interception schemes for
the same interception class will not be interoperable.
Defining an alternative interception class mechanism for
incorporation into GIST should be considered as a very radical step,
and all alternatives should be considered before taking this path.
The main reason for this is that the mechanism will necessarily
require additional operations on every packet passing through the
affected router interfaces. A number of considerations should be
taken into account:
o Although the interception mechanism need only be deployed on
routers that actually need it (probably for a new NSLP),
deployment may be constrained if the mechanism requires
modification to the hardware of relevant routers and/or needs to
await modification of the software by the router vendor.
o Typically, any packet fields to be examined should be near the
header of the packet so that additional memory accesses are not
needed to retrieve the values needed for examination.
Manner, et al. Informational [Page 19]
RFC 5978 NSIS User and Extension Guide October 2010
o The logic required to determine if a packet should be intercepted
needs to be kept simple to minimize the extra per-packet
processing.
o The mechanism should be applicable to both IPv4 and IPv6 packets.
o Packet interception mechanisms potentially provide an attack path
for denial-of-service attacks on routers, in that packets are
diverted into the "slow path" and hence can significantly increase
the load on the general processing capability of the router. Any
new interception mechanism needs to be carefully designed to
minimize the attack surface.
Packet interception mechanisms are identified by an "interception
class" which is supplied to GIST through the Application Programming
Interface for each message sent.
o New packet interception mechanisms will generally require
allocation of one or more new Interception-class-IDs. This does
not necessarily need to be placed in an IANA registry as it is
primarily used as a parameter in the API between the NSLPs and
GIST and may never appear on the wire, depending on the mechanism
employed; all that is required is consistent interpretation
between the NSLPs and GIST in each applicable node. However, if,
as is the case with the current RAO mechanism [GIST-RAO], the
scheme distinguishes between multiple packet interception classes
by a value carried on the wire (different values of RAO parameter
for the RAO mechanism in GIST), an IANA registry may be required
to provide a mapping between interception classes and on-the-wire
values as discussed in Section 6 of [GIST-RAO].
8.2.5. Use of Alternative NAT Traversal Mechanisms
The mechanisms proposed for both legacy NAT traversal (Section 7.2.1
of the GIST specification [RFC5971]) and GIST-aware NAT traversal
(Section 7.2.2 of the GIST specification [RFC5971]) can be extended
or replaced. As discussed above, extension of NAT traversal may be
needed if a new MRM is deployed. Note that there is extensive
discussion of NAT traversal in the NAT/firewall NSLP specification
[RFC5973].
8.2.6. Additional Error Identifiers
Making extensions to any of the above items may result in having to
create new error modes. See Section 9 and Appendix A.4.1 - A.4.3 of
the GIST specification [RFC5971].
Manner, et al. Informational [Page 20]
RFC 5978 NSIS User and Extension Guide October 2010
o Additional error identifiers require allocation of new error
code(s) and/or subcode(s) and may also require allocation of
Additional Information types. These are all allocated on a first-
come, first-served basis by IANA [RFC5971].
8.2.7. Defining New Objects To Be Carried in GIST
The A/B (extensibility) flags in each signaling object carried in
NSIS protocols enable the community to specify new objects applicable
to GIST that can be carried inside a signaling session without
breaking existing implementations. See Appendix A.2 of the GIST
specification [RFC5971]. The A/B flags can also be used to indicate
in a controlled fashion that a certain object must be understood by
all GIST nodes, which makes it possible to probe for the support of
an extension. One such object already designed is the "Peering
Information Object (PIO)" [PEERING-DATA] that allows a Query message
to carry additional peering data to be used by the recipient in
making the peering decision.
o New objects require allocation of a new Object Type ID either by
IETF review of a specification or through another acceptable
published specification [RFC5971].
8.2.8. Adding New Message Types
Major modifications could be made by adding additional GIST message
types and defining appropriate processing. It might be necessary to
define this as a new version of the protocol. A field is provided in
the GIST Common Header containing the version number. GIST currently
has no provision for version or capability negotiation that might be
needed if a new version was defined.
o New GIST Message Types require allocation of a new GIST Message
Type ID either by IETF review of a specification or expert review
[RFC5971].
8.3. QoS NSLP
The QoS NSLP provides signaling for QoS reservations on the Internet.
The QoS NSLP decouples the resource reservation model or architecture
(QoS model) from the signaling. The signaling protocol is defined in
Quality-of-Service NSLP (QoS NSLP) [RFC5974]. The QoS models are
defined in separate specifications, and the QoS NSLP can operate with
one or more of these models as required by the environment where it
is used. It is anticipated that additional QoS models will be
developed to address various Internet scenarios in the future.
Extensibility of QoS models is considered in Section 8.4.
Manner, et al. Informational [Page 21]
RFC 5978 NSIS User and Extension Guide October 2010
The QoS NSLP specifically mentions the possibility of using
alternative Message Routing Methods (MRMs), apart from the general
ability to extend NSLPs using new objects with the standard A/B
extensibility flags to allow them to be used in new and old
implementations.
There is already work to extend the base QoS NSLP and GIST to enable
new QoS signaling scenarios. One such proposal is the Inter-Domain
Reservation Aggregation aiming to support large-scale deployment of
the QoS NSLP [RESV-AGGR]. Another current proposal seeks to extend
the whole NSIS framework towards path-decoupled signaling and QoS
reservations [HYPATH].
8.4. QoS Specifications
The QoS Specification template (QSPEC) is defined in [RFC5975]. This
provides the language in which the requirements of specific QoS
models are described. Introduction of a new QoS model involves
defining a new QSPEC. In order to have a new QSPEC allocated by
IANA, there must be an acceptable published specification that
defines the specific elements within the QSPEC used in the new model.
See [RFC5975] for details.
The introduction of new QoS models is designed to enable deployment
of NSIS-based QoS control in specific scenarios. One such example is
the Integrated Services Controlled Load Service for NSIS [CL].
A key feature provided by defining the QSPEC template is support of a
common language for describing QoS requirements and capabilities,
which can be reused by any QoS models intending to use the QoS NSLP
to signal their requirements for traffic flows. The commonality of
the QSPEC parameters ensures a certain level of interoperability of
QoS models and reduces the demands on hardware that has to implement
the QoS control. Optional QSPEC parameters support the extensibility
of the QoS NSLP to other QoS models in the future; new QSPEC
parameters can be defined in the document that specifies a new QoS
model. See Sections 4.4 and 7 of [RFC5975].
The QSPEC consists of a QSPEC version number, QSPEC objects, plus
specification of processing and procedures that can be used to build
many QoS models. The definition of a QSPEC can be revised without
necessarily changing the version if the changes are functionally
backwards compatible. If changes are made that are not backwards
compatible, then a new QSPEC version number has to be assigned. Note
that a new QSPEC version number is not needed just because additional
QSPEC parameters are specified; new versions will be needed only if
the existing functionality is modified. The template includes
version negotiation procedures that allow the originator of an NSLP
Manner, et al. Informational [Page 22]
RFC 5978 NSIS User and Extension Guide October 2010
message to retry with a lower QSPEC version if the receiver rejects a
message because it does not support the QSPEC version signaled in the
message. See Section 3.2 of [RFC5975].
o Creation of a new, incompatible version of an existing QSPEC
requires allocation of a new QSPEC version number that is
documented in a permanent and readily available public
specification. See [RFC5975].
o Completely new QSPECs can also be created. Such new QSPECs
require allocation of a QSPEC type that is documented in a
permanent and readily available public specification. Values are
also available for local or experimental use during development.
See [RFC5975].
o Additional QSPEC procedures can be defined requiring allocation of
a new QSPEC procedure number that is documented in a permanent and
readily available public specification. Values are also available
for local or experimental use during development. See [RFC5975].
o Additional QSPEC parameters and associated error codes can be
defined requiring a permanent and readily available public
specification document. Values are also available for local or
experimental use during development. See [RFC5975].
8.5. NAT/Firewall NSLP
The NAT/firewall signaling can be extended broadly in the same way as
the QoS NSLP by defining new parameters to be carried in NAT/firewall
NSLP messages. See Section 7 of [RFC5973]. No proposals currently
exist to fulfill new use cases for the protocol.
8.6. New NSLP Protocols
Designing a new NSLP is both challenging and easy.
New signaling applications with associated NSLPs can be defined to
work in parallel or replace the applications already defined by the
NSIS working group. Applications that fit into the NSIS framework
will be expected to use GIST to provide transport of signaling
messages and appropriate security facilities that relieve the
application designer of many "lower-level" problems. GIST provides
many important functions through the API that it exposes to the code
of the signaling application layer, and allows the signaling
application programmer to offload various tasks to GIST, e.g., the
channel security, transport characteristics, and signaling node
discovery.
Manner, et al. Informational [Page 23]
RFC 5978 NSIS User and Extension Guide October 2010
Yet, on the other hand, the signaling application designer must take
into account that the network environment can be dynamic, both in
terms of routing and node availability. The new NSLP designer must
take into account at least the following issues:
o Routing changes, e.g., due to mobility: GIST sends network
notifications when something happens in the network, e.g., peers
or routing paths change. All signaling applications must be able
to handle these notifications and act appropriately. GIST does
not include logic to figure out what the NSLP would want to do due
to a certain network event. Therefore, GIST gives the
notification to the application, and lets it make the right
decision.
o GIST indications: GIST will also send other notifications, e.g.,
if a signaling peer does not reply to refresh messages, or a
certain NSLP message was not successfully delivered to the
recipient. NSLP applications must also be able to handle these
events. Appendix B in the GIST specification discusses the GIST-
NSLP API and the various functionality required, but implementing
this interface can be quite challenging; the multitude of
asynchronous notifications that can arrive from GIST increases the
implementation complexity of the NSLP.
o Lifetime of the signaling flow: NSLPs should inform GIST when a
flow is no longer needed using the SetStateLifetime primitive.
This reduces bandwidth demands in the network.
o NSLP IDs: NSLP messages may be multiplexed over GIST MAs. The new
NSLP needs to use a unique NSLPID to ensure that its messages are
delivered to the correct application by GIST. A single NSLP could
use multiple NSLPIDs, for example, to distinguish different
classes of signaling nodes that might handle different levels of
aggregation of requests or alternative processing paths. Note
that unlike GIST, the NSLPs do not provide a protocol versioning
mechanism. If the new NSLP is an upgraded version of an existing
NSLP, then it should be distinguished by a different NSLPID.
* A new generally available NSLP requires IESG approval for the
allocation of a new NSLP ID [RFC5971]
o Incremental deployment: It would generally be unrealistic to
expect every node on the signaling path to have a new NSLP
implemented immediately. New NSLPs need to allow for this. The
QoS and NAT/firewall NSLPs provide examples of techniques such as
proxy modes that cater for cases where the data flow originator
and/or receiver does not implement the NSLP.
Manner, et al. Informational [Page 24]
RFC 5978 NSIS User and Extension Guide October 2010
o Signaling Message Source IP Address: It is sometimes challenging
for an NSLP originating a signaling message to determine the
source IP address that should be used in the signaling messages,
which may be different from the data flow source address used in
the MRI. This challenge occurs either when a node has multiple
interfaces or is acting as a proxy for the data flow originator
(typically expected to occur during the introduction of NSIS when
not all nodes are NSIS enabled). A proxy signaling flow
originator generally needs to know and use the correct data flow
source IP address, at least initially. As discussed in Section
5.8.1.2 of [RFC5971], the signaling flow originator may choose to
alter the source IP address after the initial Query message has
established the flow path in order that ICMP messages are directed
to the most appropriate node. In the proxy case, the data flow
originator would be unaware of the signaling flow, and ICMP
messages relating to the signaling would be meaningless if passed
on to the data flow originator. Hence, it is essential that an
NSLP is aware of the position and role of the node on which it is
instantiated and has means of determining the appropriate source
address to be used and ensuring that it is used on signaling
packets.
o New MRMs: GIST currently defines two Message Routing Methods, and
leaves the door open for new ideas. Thus, it is possible that a
new NSLP also requires a new MRM; path-decoupled routing being one
example.
o Cooperation with other NSLPs: Some applications might need
resources from two or more different classes in order to operate
successfully. The NSLPs managing these resources could operate
cooperatively to ensure that such requests were coordinated to
avoid wasting signaling bandwidth and prevent race conditions.
It is essential that the security considerations of a new NSLP are
carefully analyzed. NSIS NSLPs are deployed in routers as well as
host systems; a poorly designed NSLP could therefore provide an
attack vector for network resources as well as end systems. The NSLP
must also support authorization of users and must allow the use of
the GIST authentication and integrity protection mechanisms where
users deem them to be necessary.
The API between GIST and NSLPs (see Appendix B in [RFC5971]) is very
important to understand. The abstract design in the GIST
specification does not specify the exact messaging between GIST and
the NSLPs but gives an understanding of the interactions, especially
what kinds of asynchronous notifications from GIST the NSLP must be
prepared to handle: the actual interface will be dependent on each
implementation of GIST.
Manner, et al. Informational [Page 25]
RFC 5978 NSIS User and Extension Guide October 2010
Messages transmitted by GIST on behalf of an NSLP are identified by a
unique NSLP identifier (NSLPID). NSLPIDs are 16-bit unsigned numbers
taken from a registry managed by IANA and defined in Section 9 of the
GIST specification [RFC5971].
A range of values (32704-32767) is available for Private and
Experimental use during development. Any new signaling application
that expects to be deployed generally on the Internet needs to use
the registration procedure "IESG Approval" in order to request
allocation of unique NSLPID value(s) from the IANA registry. There
is additional discussion of NSLPIDs in Section 3.8 of the GIST
specification.
9. Security Considerations
This document provides information to the community. It does not
itself raise new security concerns.
However, any extensions that are made to the NSIS protocol suite will
need to be carefully assessed for any security implications. This is
particularly important because NSIS messages are intended to be
actively processed by NSIS-capable routers that they pass through,
rather than simply forwarded as is the case with most IP packets. It
is essential that extensions provide means to authorize usage of
capabilities that might allocate resources and recommend the use of
appropriate authentication and integrity protection measures in order
to exclude or adequately mitigate any security issues that are
identified.
Authors of new extensions for NSIS should review the analysis of
security threats to NSIS documented in [RFC4081] as well as
considering whether the new extension opens any new attack paths that
need to be mitigated.
GIST offers facilities to authenticate NSIS messages and to ensure
that they are delivered reliably. Extensions must allow these
capabilities to be used in an appropriate manner to minimize the
risks of NSIS messages being misused and must recommend their
appropriate usage.
If additional transport protocols are proposed for use in association
with GIST, an appropriate set of compatible security functions must
be made available in conjunction with the transport protocol to
support the authentication and integrity functions expected to be
available through GIST.
Manner, et al. Informational [Page 26]
RFC 5978 NSIS User and Extension Guide October 2010
10. Acknowledgements
This document combines work previously published as two separate
documents: "What is Next Steps in Signaling anyway - A User's Guide
to the NSIS Protocol Family" written by Roland Bless and Jukka
Manner, and "NSIS Extensibility Model" written by John Loughney.
Max Laier, Nuutti Varis and Lauri Liuhto have provided reviews of the
"User's Guide" and valuable input. Teemu Huovila also provided
valuable input on the later versions.
The "Extensibility Model" borrowed some ideas and some text from RFC
3936 [RFC3936], "Procedures for Modifying the Resource ReSerVation
Protocol (RSVP)". Robert Hancock provided text for the original GIST
section, since much modified, and Claudia Keppler has provided
feedback on this document, while Allison Mankin and Bob Braden
suggested that this document be worked on.
11. References
11.1. Normative References
[RFC3726] Brunner, M., "Requirements for Signaling Protocols",
RFC 3726, April 2004.
[RFC4080] Hancock, R., Karagiannis, G., Loughney, J., and S.
Van den Bosch, "Next Steps in Signaling (NSIS):
Framework", RFC 4080, June 2005.
[RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats
for Next Steps in Signaling (NSIS)", RFC 4081,
June 2005.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26,
RFC 5226, May 2008.
[RFC5971] Schulzrinne, H. and R. Hancock, "GIST: General
Internet Signalling Transport", RFC 5971,
October 2010.
[RFC5973] Stiemerling, M., Tschofenig, H., Aoun, C., and E.
Davies, "NAT/Firewall NSIS Signaling Layer Protocol
(NSLP)", RFC 5973, October 2010.
[RFC5974] Manner, J., Karagiannis, G., and A. McDonald, "NSIS
Signaling Layer Protocol (NSLP) for Quality-of-
Service Signaling", RFC 5974, October 2010.
Manner, et al. Informational [Page 27]
RFC 5978 NSIS User and Extension Guide October 2010
[RFC5975] Ash, G., Bader, A., Kappler, C., and D. Oran, "QSPEC
Template for the Quality-of-Service NSIS Signaling
Layer Protocol (NSLP)", RFC 5975, October 2010.
11.2. Informative References
[CL] Kappler, C., Fu, X., and B. Schloer, "A QoS Model for
Signaling IntServ Controlled-Load Service with NSIS",
Work in Progress, April 2010.
[EST-MRM] Bless, R., "An Explicit Signaling Target Message
Routing Method (EST-MRM) for the General Internet
Signaling Transport (GIST) Protocol", Work
in Progress, June 2010.
[GIST-DCCP] Manner, J., "Generic Internet Signaling Transport
over DCCP and DTLS", Work in Progress, June 2007.
[GIST-RAO] Hancock, R., "Using the Router Alert Option for
Packet Interception in GIST", Work in Progress,
November 2008.
[GIST-SCTP] Fu, X., Dickmann, C., and J. Crowcroft, "General
Internet Signaling Transport (GIST) over Stream
Control Transmission Protocol (SCTP) and Datagram
Transport Layer Security (DTLS)", Work in Progress,
May 2010.
[HYPATH] Cordeiro, L., Curado, M., Monteiro, E., Bernardo, V.,
Palma, D., Racaru, F., Diaz, M., and C. Chassot,
"GIST Extension for Hybrid On-path Off-path Signaling
(HyPath)", Work in Progress, February 2008.
[NSIS-AUTH] Manner, J., Stiemerling, M., Tschofenig, H., and R.
Bless, "Authorization for NSIS Signaling Layer
Protocols", Work in Progress, July 2008.
[PEERING-DATA] Manner, J., Liuhto, L., Varis, N., and T. Huovila,
"Peering Data for NSIS Signaling Layer Protocols",
Work in Progress, February 2008.
[RAO-BAD] Rahman, R. and D. Ward, "Use of IP Router Alert
Considered Dangerous", Work in Progress,
October 2008.
[RESV-AGGR] Doll, M. and R. Bless, "Inter-Domain Reservation
Aggregation for QoS NSLP", Work in Progress,
July 2007.
Manner, et al. Informational [Page 28]
RFC 5978 NSIS User and Extension Guide October 2010
[RFC1633] Braden, B., Clark, D., and S. Shenker, "Integrated
Services in the Internet Architecture: an Overview",
RFC 1633, June 1994.
[RFC2205] Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
Jamin, "Resource ReSerVation Protocol (RSVP) --
Version 1 Functional Specification", RFC 2205,
September 1997.
[RFC3692] Narten, T., "Assigning Experimental and Testing
Numbers Considered Useful", BCP 82, RFC 3692,
January 2004.
[RFC3936] Kompella, K. and J. Lang, "Procedures for Modifying
the Resource reSerVation Protocol (RSVP)", BCP 96,
RFC 3936, October 2004.
[RFC4094] Manner, J. and X. Fu, "Analysis of Existing Quality-
of-Service Signaling Protocols", RFC 4094, May 2005.
[TWO-LEVEL] Braden, R. and B. Lindell, "A Two-Level Architecture
for Internet Signaling", Work in Progress,
November 2002.
Manner, et al. Informational [Page 29]
RFC 5978 NSIS User and Extension Guide October 2010
Authors' Addresses
Jukka Manner
Aalto University
Department of Communications and Networking (Comnet)
P.O. Box 13000
FIN-00076 Aalto
Finland
Phone: +358 9 470 22481
EMail: jukka.manner@tkk.fi
URI: http://www.netlab.tkk.fi/~jmanner/
Roland Bless
Institute of Telematics, Karlsruhe Institute of Technology (KIT)
Zirkel 2, Building 20.20
P.O. Box 6980
Karlsruhe 76049
Germany
Phone: +49 721 608 6413
EMail: bless@kit.edu
URI: http://tm.kit.edu/~bless
John Loughney
Nokia
955 Page Mill Road
Palo Alto, CA 94303
USA
Phone: +1 650 283 8068
EMail: john.loughney@nokia.com
Elwyn Davies (editor)
Folly Consulting
Soham
UK
EMail: elwynd@folly.org.uk
URI: http://www.folly.org.uk
Manner, et al. Informational [Page 30]