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|
This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts.
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This Internet-Draft will expire on August 16, 2004.
Copyright (C) The Internet Society (2004). All Rights Reserved.
This document discusses migration issues towards NSIS NAT/FW NSLP enabled NATs and Firewalls. The document will serve as input to the NSIS NATFW NSLP document.
1.
Introduction
2.
Terminology
3.
NSIS unaware NAT Traversal
4.
Unilateral NSIS signaling
5.
NSIS unaware Firewall Traversal
6.
NATFW NSLP NTLP requirements
7.
Security Considerations
8.
Open issues
§
Normative References
§
Informative References
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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The overall NSIS protocol suite (including the NATFW NSLP) is impacted by NSIS NATFW NSLP unaware NATs and Firewalls, this document covers impacts as well as some suggestions to ease the deployments of the NSIS protocol suite until the installed base on NATs and Firewalls migrates to NSIS.
The NATFW NSLP should allow an end host supporting NSIS to operate properly without the need of supporting true end-to-end NSIS signaling to its application correspondent. This is very practical during the initial phases of the NSIS migration and is applicable in simple network configurations not affected by asymmetric routing. In the early phases of the NSIS NATFW NSLP migration, this situation will occur quite frequent and hence this scenario must be supported.
The NSIS protocol should traverse NSIS unaware NATs (and possibly Firewalls) to allow a smoother deployment of, for example, Qos NSLP in today's networks. To provide a smooth migration it is necessary to understand the coexistence of NSIS aware and unware NATs and Firewalls.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [1].
The terminology used in this document is defined in [2].
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This section discusses how an NE with any NSLP could still operate when an NSIS unaware NAT is on the data path. The detection of an NSIS unaware NAT could be a feature of the NTLP [3], allowing its usage on any NE regardless of the supported NSLPs.
Several NSIS independent approaches could be used by the NE to learn its global scoped address in order to use it for its hosted NSLPs. In this version of the document, only the STUN protocol [5] is considered as means to acquire the global scoped address; the next versions will consider other approaches.
+---------------------------------------+
| | +--------+
| +----------+ | | STUN |
| |Apps | | | Server |
| +----------+ +---+| +--------+
| | STUN | |NAT||
| | CLIENT | | ||
| |__________| +---+|
| |ANY_NSLP | |
| | NI/NR | |
| +----------+ |
| Host A |
+---------------------------------------+
| STUN usage for NSIS unaware NATs |
Within the initial stages of the NSIS migration, NE functions will be co-hosting a STUN client that was already present on the application end-host. Within Host A, shown in Figure 1, the NSIS API could invoke the services of the STUN client (as shown in Figure 2) upon determination that an NSIS unaware NAT was on the path.This would allow applications using UDP transport to work (only applicable for cone NAT variants [5]).
+-----------------+
___________| NSIS aware NAT |_________
| | Determination | |
NSIS | +-----------------+ | NSIS
Aware | | Unaware
| |
| |
V V
+-------------------+ +------------+
|Proceed with | If not UDP |Used data |
|normal NR operation| +--------|transport |
+-------------------+ | |protocol |
| +------------+
| | If UDP
V |
+-------------+ |
|Log error | |
|to app layer | |
+-------------+ V
+-------------+
| Invoke STUN |
| Client |
+------+------+
|
|
|
V
+------------+
| Send STUN |
| binding |
| request |
+-----+------+
|
V
+-------------------------+
|Standard STUN operations |
+-------------------------+
| Interactions with a STUN client |
NSLPs would use the STUN returned global scoped address for the flow id [3].To allow NSIS signaling to be received by the NR on host A, without impacting existing applications (i.e. without explicitly providing the address and port of the NSIS recipient in the application signaling), the NSIS protocols would need to use NTLP datagram mode transport (as defined in [3]). This would imply that the NTLP will be using the same port as the data flows, this might complicate the proposed mode of operations (and might not meet the expected performance). The next version of the draft will discuss whether this approach would be practical based on received feedback from implementors.
Subsequently we discuss how the NATFW NSLP could co-exist with interim NAT traversal mechanisms described in [8]. In Figure 3, a STUN client (Host A) [5], an NE (Host B), a host using a Media Proxy [8] and host using a TURN client [9] co-exist in the same network with a NATFW NSLP aware NAT. There are no reasons for the existing mechanisms to be mutually exclusive every host could continue using the existing interim solutions, meanwhile the unilateral NSIS signaling would be used until both ends support the NSIS NATFW NSLP.
+---------------------------+
| _|__1______.STUN Server
|STUN Client ----'''''''''' |
| Host A | App server
| 2 _..NAT++ | .-'
| NI/NR __.--'' | 3 .'+
| Host B -'' | Media Proxy.-'
| |
| |
| Host C |
| 4 |
| Turn Client---------------+---------- TURN Server
| Host D |
| |
+---------------------------+
| Coexistence of NSIS NATFW NSLP and existing NAT traversal mechanisms |
| TOC |
When NSIS NAT/FW signaling will start to be deployed, it is quite possible that an NI sends an NSIS message without having an NR to respond to it. The NATFW NSLP should be able to handle this type of deployments. NSIS NATFW NSLP signaling for NAT binds is already local within the trust domain (the Reserve External Address is intercepted by the edge NAT, ref [2], however this is not the case with firewall signaling that should be end to end.
Since the purpose of this section is to discuss how are end to end signaled messages handled when no NRs are available on the end-host only Firewalls (the NFs) are discussed within the example networks.
There are two interesting cases to be analyzed:
- Approach 1: Implicit (not explicitly scoped) localized signaling:
- The local trust domain (from an NI perspective) has at least one NSIS aware Firewall, there is no NR on the far end as well as no NSIS aware NAT or Firewall. This approaches is similar to [13], however the NSIS messages do not included any scoping information. Figure 4 shows this scenario graphically.
+-----------------------+ +--------------------+ |+----------+ | | +----------+ ||App client| | | |App client| ||NI/NR | FW++ | ,---------. | +----------+ |+----------+ ''''''' The net ---. Host B | | Host A | `---------' | | | | | | | Net A | | Net B | +-----------------------+ +--------------------+
Implicit localized signaling
- Approach 2: Missing trust with far end host's NFs:
- The local trust domain has no NSIS aware Firewall, there is no NR at the far end but there is at least an NSIS aware firewall with which the local NI has no direct trust relation (which implies an authorization issue and possibly authentication issues). The main addition to the issue discussed in the localized signaling case above (determination of the last NE on the path and response to the NSIS message by the last NE) is the lack of trust relations with the NI. Figure 5 shows this scenario graphically.
+-----------------------+ +--------------------+ |+----------+ | | +----------+ ||App client| | | |App client| ||NI/NR | | ,---------. | FW++ +----------+ |+----------+ ''''''' The net ---. Host B | | Host A | `---------' | | | | | | | Net A | | Net B | +-----------------------+ +--------------------+
Missing trust with the remote host's network
In approach (1), the NI sends its firewall policy rule creation message, it traverses the first NF (its own firewall) but there is no NR to respond back. If we consider to have a response timer on the last NF being traversed by an NATFW NSLP message then if no response is received to the NSIS message, the last NF will respond back to the NI with a notification of no far end NR response. This will imply that the signaling will be scoped to the last NF on the path that responded back. Using the network deployment shown in Figure 4, the following mode of operation would apply:
Host A Host B
NI FW++ Expected NR
| | |
|1-NSIS Init msg | |
|----------------> | |
| |2-NSIS Init msg |
| | +---------------> |
| | |NATFW NSLP ON |
| | | |
| | | |
| | | |
| | | Timeout |
3-NSIS Init msg Ack| V |
|No NR | |
|<.................| |
| Detecting the last NSIS peer |
Figure 7 provides the message sequences when more than one NSIS aware NAT or Firewall is deployed within the same trust domain. Upon determination of a previous NSIS hop, an NSIS aware node will notify the previous NSIS hop of its existence to avoid launching the timer that triggers sending of an NSIS message back to the NI. The current NTLP message association establishment procedures supports this behavior. The last NF on the path will launch the timer since no valid downstream NSIS neighbor responded back.
Trust domain A Trust domain B
<..........................................> <-------->
Host A Host B
NI FW++ FW++ Expected NR
| | | |
| NSIS Init msg | | |
| ----------------> | NSIS Init msg | |
| | ---------------> | NSIS Init msg |
| | NATFW NSLP ON |---------------->|
| | | | with Token |
| | Valid . | NATFW NSLP ON |
| | NSIS Neighbor | | |
| |<-----------------| | |
| |----------------->| | Timeout |
| | Ack | | |
| | | | |
| | | | |
| | | | |
| | | V |
| | <................+ |
| | NSIS Init msg Ack| |
| NSIS Init msg Ack | No NR | |
| No NR | | |
| <.................| | |
| Detecting the last NSIS peer (multiple FWs) |
In approach (2), the NI sends its firewall policy rule creation message, it traverses
the FW hosted in Host B's network, but host A is not authorized to install a policy
rule unless the policy rule creation is approved by a trusted entity within Net B.
Unfortunately Host B was not yet upgraded to support the NATFW NSLP, another entity
needs to authorize the policy rule installation.
Potentially a trusted
third party already aware of the application session held between Host A and Host B
could provide an authorization token to Host A [11], the token
would be encapsulated within the NATFW NSLP message and would allow the NSIS aware
Firewall in Net B to authorize Host A's requested policy rule to be installed. This
approach would obviously require to put in place a mechanism to provide the
authorization token to Host A. The token could be requested by the NI and included
in the NSLP signaling by default or after receiving an error message from the far
end NSIS aware Firewall indicating that authorization data is required. The
authorization token would need to be associated with the identity of the NI,
associating the authorization token with an IP address is not sufficient, and could
lead to issues if the IP address was not valid due to address translation occurring
on the path, a proper mechanism should be put in place to allow proper
authentication of the entitled token user.
Figure 8 shows the architecture with two different networks and the trusted third party which creates the authorization. Figure 9 provides a message flow for authorization token handling.
+---------------+
| Authorization|1-Generate Token
| mediator |
.'--------------+
.' \
2-Provide .-' \
Token .' \
.' \
.' \4-Check token
.-' \ validity
+-----------.'----------+ ++----------------+
|+--------.'+ | | \ +----------+
||App client| | | \ |App client|
||NI/NR +-------. | ,-=.----.-. | FW++ +----------+
|+----------+ `---------'The net `-------- Host B |
| Host A | `---------' | |
| | 3-Send | |
| Network A | NSLP msg with | Network B |
+-----------------------+ Token +-----------------+
| Authorization Token Handling |
Trust domain A Trust domain B
<........................> <--------------------->
Host A Host B
NI FW FW++ Expected NR
| | | |
| NSIS Init msg | | |
| ------------------+----------------> | |
| | | NSIS Init msg |
| | | +-------------->|
| | | NATFW NSLP ON |
| | NSIS ERROR . |
| <....................................| |
| |Need Authorization| |
| NSIS Init msg | | |
| ------------------------------------>| |
| with Token | | |
| | | NSIS Init msg |
| | |---------------->|
| | | | with Token |
| | Valid + | NATFW NSLP ON |
| | NSIS Neighbor | | |
| |<-----------------| | Timeout |
| |----------------->| | |
| NSIS Init msg Ack | Ack | | |
| No NR | <................| V |
| <.................| NSIS Init msg Ack| |
| | No NR | |
| Authorization Token Message Flow |
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In case an NSIS unaware firewall is traversed by NSIS messages, NSIS messages should be allowed to go through it, as well as the exchanged data flows between the user application clients. This is not necessarily an obvious task to perform in case the NSIS messages cannot be identified by the NSIS unaware firewall. Same applies for the user application data flows.
NSIS message identification should be supported by existing firewalls.
Currently firewalls support flow identification by using the 5 tuple or a sub-set of
it. The authors are still expecting feedback from firewall vendors to see if we can
assume that existing firewalls will not drop packets including the the Router Alert
Option (RAO) [12]. In case existing firewalls drop packets
having the router alert option, then the RAO should not be the only element of the
used identification filter.
User application data flow identification, should be deterministic at a specific address and port range level. This means that the application clients uses a combination of an address and specific transport port range.This combination should be configured on the firewall.
In case a NAT is deployed on the path and it is NSIS-NATFW, the assigned bind should be consistent with policy rules configured with the NSIS unaware firewall.
Even though the deployed Firewall is not NSIS aware, the application data would still be forwarded if existing interim solutions were used such as a mix of stateless policy rules and flow based states with initial packets sent in the outbound direction (inside to outside a trust domain).
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In this section we list two requirements for the NTLP raised by this document.
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This document discusses various security issues for NAT/Firewall signaling in migration scenarios.
Further security considerations can be found in [2].
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Working on this document we identified to the following open issues and actions that need to be taken:
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| [1] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", March 1997. |
| [2] | Stiemerling, M., Martin, M., Tschofenig, H. and C. Aoun, "A NAT/Firewall NSIS Signaling Layer Protocol (NSLP)", DRAFT draft-ietf-nsis-nslp-natfw-01.txt, February 2004. |
| [3] | "GIMPS: General Internet Messaging Protocol for Signaling", draft-draft-ietf-nsis-ntlp-00 (work in progress), October 2003. |
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| [4] | A. Huttunen et all, A., "UDP Encapsulation of IPsec Packets", DRAFT draft-ietf-ipsec-udp-encaps-07.txt, Jan 2003. |
| [5] | Rosenberg, J., Weinberger, J., Huitema, C. and R. Mahy, "STUN - Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)", RFC 3489, March 2003. |
| [6] | Handley, M. and V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. |
| [7] | ITU-T SG16, "Packet-based multimedia communications systems", ITU-T H.323, November 2000. |
| [8] | Rosenberg, J., "NAT and Firewall Scenarios and Solutions for SIP", draft-rosenberg-sipping-nat-scenarios-00 (work in progress), November 2001. |
| [9] | Rosenberg, J., "Traversal Using Relay NAT (TURN)", draft-rosenberg-midcom-turn-01 (work in progress), March 2003. |
| [10] | Swale, R., Mart, P., Sijben, P., Brim, S. and M. Shore, "Middlebox Communications (midcom) Protocol Requirements", RFC 3304, August 2002. |
| [11] | Hamer, L-N., Gage, B. and H. Shieh, "Framework for Session Set-up with Media Authorization", RFC 3521, April 2003. |
| [12] | Katz, D., "IP Router Alert Option", RFC 2113, February 1997 (HTML, XML). |
| [13] | Manner, J., "Localized RSVP", draft-manner-lrsvp-03 (work in progress), January 2004. |
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| Cedric Aoun | |
| Nortel Networks | |
| France | |
| EMail: | cedric.aoun@nortelnetworks.com |
| Marcus Brunner | |
| Network Laboratories, NEC Europe Ltd. | |
| Kurfuersten-Anlage 36 | |
| Heidelberg 69115 | |
| Germany | |
| Phone: | +49 (0) 6221 905 11 29 |
| EMail: | brunner@ccrle.nec.de |
| URI: | http://www.brubers.org/marcus |
| Martin Stiemerling | |
| Network Laboratories, NEC Europe Ltd. | |
| Kurfuersten-Anlage 36 | |
| Heidelberg 69115 | |
| Germany | |
| Phone: | +49 (0) 6221 905 11 13 |
| EMail: | stiemerling@ccrle.nec.de |
| URI: | |
| Miquel Martin | |
| Network Laboratories, NEC Europe Ltd. | |
| Kurfuersten-Anlage 36 | |
| Heidelberg 69115 | |
| Germany | |
| Phone: | +49 (0) 6221 905 11 16 |
| EMail: | miquel.martin@ccrle.nec.de |
| URI: | |
| Hannes Tschofenig | |
| Siemens AG | |
| Otto-Hahn-Ring 6 | |
| Munich 81739 | |
| Germany | |
| Phone: | |
| EMail: | Hannes.Tschofenig@siemens.com |
| URI: |
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