Internet Engineering Task Force Juha Heinanen INTERNET DRAFT Song Networks Expires May 2002 November, 2001 Directory/LDP Based Ethernet VPNs Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026. 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. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet- Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract This memo describes how provider based Ethernet VPNs can be implemented using a directory (such as DNS) and LDP for PE discovery and label distribution. 1. Introduction This memo describes a simple mechanism to implement provider based bridged Ethernet VPNs using a directory and LDP [1] for PE discovery and label distribution. The directory can be anything where the IP addresses of the PE routers of a VPN can be stored and queried from. In this memo we have chosen to use DSN directory as proposed in [2]. An advantage of a directory/LDP based solution for provider based VPNs is that it doesn't require BGP implementation or configuration complexity in the PE routers and can be easily deployed also in inter-AS cases where the VPN sites are attached to PEs in more than Heinanen Directory/LDP Based Ethernet VPNs [Page 1] INTERNET DRAFT October, 2001 one AS. The choice of DNS for the directory is justified because it is already in wide use and can be deployed without any new standardization effort. Similar DNS/LDP based solution can also be applied to provider based Virtual Circuit and Virtual Router VPNs. If there is sufficient interest, the details will be specified in later memos. 2. Addition of Sites 2.1 Configuration Actions DNS/LDP based Ethernet VPNs are very easy to provision. Only the following two configuration actions are needed when a new site (CE device) is added to a VPN: (1) If the PE device (PE for short) does not previously connect any sites of this VPN, the IP address of the PE is configured to DNS under domain name vpn-number.as-number.domain where "vpn-number" and "as-number" are components of the VPN ID (Route Distinguisher [3]) of the VPN and "domain" is the domain of the administrative "owner", (e.g., an ISP) of the VPN. (2) The port of the PE to which the site is connected to is configured to belong to the VPN. This is done by specifying the domain, type, and VPN ID of the VPN. This document covers the case where the type of the VPN is "Ethernet". Note that also in the case of a multi-provider VPN, the administrative "owner" of any VPN is the single body that operates the master DNS server for the VPN zone. The "owner" of a VPN MAY choose to make all updates to the zone data of the VPN itself or MAY allow other providers to dynamically update the zone data. In the latter case, the use of secure dynamic updates [4] is recommended. 2.2 Protocol Actions After the above configuration actions, the following protocol actions take place in sequence at the PE of the new site if the PE of the new site doesn't previously connect site(s) of the VPN: (1) The PE of the new site checks that its own IP address has become available in the DNS. Heinanen Directory/LDP Based Ethernet VPNs [Page 2] INTERNET DRAFT October, 2001 (2) The PE of the new site queries DNS for IP addresses of the other (remote) PEs of the VPN. (3) The PE of the new site establishes an LDP session with each of the remote PEs unless one already exists. (4) The PE of the new site sends a Label Mapping Message to each of the remote PEs that advertises a label to be used when a remote PE sends packets to the sites of the VPN at the PE of the new site. Each such label MUST uniquely identify at the PE of the new site both the VPN and the sending PE. The Label Mapping Message uses the following VPN FEC TLV: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VPN ID TLV | Address Family |VPN ID Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 8 octet VPN Identifier (Route Distinguisher) | + from RFC 2547 [3] + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Element type name: VPN Type: TBD by IANA Address Family: set to zero VPN ID Length: 8 octets The following protocol actions take place in sequence at a PE when it receives a Label Mapping message from another PE: (1) The PE checks from the DNS that the other PE belongs to the VPN of the Label Mapping Message and that it itself has at least one site in that VPN. If not, the PE responds to the Label Mapping Message with a Label Release Message and no other protocol actions take place at the PE. (2) The PE checks if it already has a label for the VPN and PE of the Label Mapping Message. If so, the PE responds to the Label Mapping Message with a Label Release Message and no other protocol actions take place at the PE. (3) The PE checks if it already has itself advertised a label to the other PE for the VPN of the Label Mapping Message. If not, the PE sends a Label Mapping Message to the other PE to be used when the other PE sends packets to the sites of the VPN at the PE. The advertised label MUST again uniquely identify at the PE Heinanen Directory/LDP Based Ethernet VPNs [Page 3] INTERNET DRAFT October, 2001 both the VPN and the other PE. If the PE of the new site already connects site(s) of this VPN, no protocol actions take place at either the PE of the new site or at the remote PEs. 3. Removal of Sites 3.1 Configuration Actions The following configuration actions are needed when an existing site (CE device) is removed from a VPN: (1) If the site to be removed is the last site of the VPN at the PE, the IP address of the PE is removed from DNS. (2) The site is removed from the VPN by unconfiguring the VPN from the port of the PE to which the site is connected to. 3.2 Protocol Actions After the above configuration actions, the following protocol actions take place at the PE of the removed site: (1) If the removed site was the last site of the VPN at the PE, the PE checks that its IP address does not anymore exist in the DNS under the zone of the VPN. (2) The PE removes any existing labels of the VPN that it had advertised to the remote PEs by sending them a Label Withdraw Message. In addition to processing the Label Withdraw Message, the following protocol actions take place when a PE receives a Label Withdraw Message from another PE: (1) The PE removes the label that it had advertised to the other PE for the VPN of the Label Withdraw Message by sending it a Label Withdraw Message. (2) If there is no remaining need to keep the LDP session up between the PE and the other PE, the PE MAY terminate the LDP session with the other PE. 4. Failure Recovery If a PE looses its LDP session with another PE having site(s) in a common VPN, the PE releases the label it has advertised to the other Heinanen Directory/LDP Based Ethernet VPNs [Page 4] INTERNET DRAFT October, 2001 PE for this VPN. The PE then tries to re-establish the LDP session until (a) the session gets established or (b) this PE or the other PE no longer have site(s) in this VPN. Once the LDP session gets established, the PE advertises to the other PE a label to be used to send packets to the site(s) of the VPN at this PE as described in section 2.2. When a PE recovers from a crash, it adds each of the configured VPN site(s) to their respective VPN(s) as described in section 2.2. 5. Exponential Back-off Behavior If any protocol action does not succeed immediately, the normal behavior is that the PE keeps on trying with exponential back-off until the action either succeeds or becomes invalid due to a change in VPN configuration. If the protocol action fails for an implementation specific prolonged period of time, the PE SHOULD notify the VPN provider about the problem via a management action. 6. Data Plane The PEs that host the sites of a VPN act as fully connected learning bridges. When PE A needs to forward an Ethernet packet to PE B, PE A prefixes the Ethernet packet by a label stack entry [5] holding the label that PE B has advertised to PE A for this VPN. PE A then sends the resulting frame to PE B in any available tunnel, such as a HIP, GRE, IPSec, VLAN, or MPLS. How a PE decides, which tunneling protocol to use to send labeled packets to another PE, is outside the scope of this memo. Usually the PE would try tunneling protocols in its own preferred order until the tunnel gets established. In most cases the availability of a tunneling protocol can be determined by out-of-band means (e.g., DNS in case of HIP and IPSec, existence of an outer tunnel in case of MPLS, or existence of a shared authentication key in case of GRE). 7. DNS Zone Update Latency In order to make addition and removal of VPN PEs as fast as possible, it is important to try to minimize the latency of VPN zone updates. This can be achieved by turning on DNS NOTIFY [6] in the master server for each VPN zone and/or by configuring zone refresh times small. 8. DNS Message Size Correct operation of directory/LDP based VPNs requires that IP addresses of all PE routers of a VPN fit into a single DNS response. Heinanen Directory/LDP Based Ethernet VPNs [Page 5] INTERNET DRAFT October, 2001 In order to be able to support large VPNs with a large number of PEs, the message size requirements of [7] also apply to DNS servers and resolvers used for implementing the mechanism of this memo. Fulfilling those requirements allows provisioning of DNS/LDP based VPNs that consist of a few hundred of PEs, which is envisioned to be more than adequate for Ethernet VPNs. 9. Security Considerations Security of directory/LDP based VPNs depends on security of the directory (DNS), LDP, and the tunneling protocol(s). Security of LDP is covered in the security section of [1]. Also the various tunneling protocol specifications have their own security sections. Regarding DNS security, the important issues related to this memo are security of zone transfers, security of dynamic updates, as well as integrity and authentication of DNS queries and responses. Dynamic updates were already discussed in section 2.1 with a recommendation to use secure dynamic updates [4]. Security of zone transfers and integrity of queries and responses are addressed by DNS extensions [8] and [9]. No DNS extensions exist for providing confidentiality for queries or responses. It is thus possible that if a party knows the VPN ID of a VPN and the zone that hosts it, the party can find out the IP addresses of PE routers that connect sites of that domain. Depending on the situation, that may or may not be an acceptable security risk. In a single-provider VPN, the DNS servers that host the VPN information can be easily fire-walled from all public access. Another way to prevent outside parties from accessing VPN information is to use DNS access lists that allow VPN zone related queries only from trusted PE routers. See [2] for additional DNS/VPN related security discussion. Acknowledgements I would like to thank Joel Halpern of Longitude Systems and Matt Squire of Hatteras Networks for their constructive comments on an earlier versions of this memo. References [1] Andersson, et al., "LDP Specification". RFC 3036, January 2001. [2] Luciani et al., "Using DNS for VPN Discovery". draft-luciani- ppvpn-vpn-discovery-00.txt, September 2001. Heinanen Directory/LDP Based Ethernet VPNs [Page 6] INTERNET DRAFT October, 2001 [3] Rosen and Rekhter, "BGP/MPLS VPNs". RFC 2547, March 1999. [4] Wellington, "Secure Domain Name System (DNS) Dynamic Update". RFC 3007, November 2000. [5] Rosen et al., "MPLS Label Stack Encoding". RFC 3032, January 2001. [6] Vixie, "A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)". RFC 1996, August 1996. [7] Gudmundsson, "DNSSEC and IPv6 A6 aware server/resolver message size requirements". draft-ietf-dnsext-message-size-04.txt, February 2001. [8] Vixie, et al., "Secret Key Transaction Authentication for DNS (TSIG)". RFC 2845, May 2000. [9] Eastlake, "Domain Name System Security Extensions". RFC 2535, March 1999. Author's Address Juha Heinanen Song Networks, Inc. Hallituskatu 16 33200 Tampere, Finland Email: jh@song.fi Full Copyright Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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Heinanen Directory/LDP Based Ethernet VPNs [Page 7] INTERNET DRAFT October, 2001 This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Heinanen Directory/LDP Based Ethernet VPNs [Page 8]