L2VPN Working Group R. Singh INTERNET-DRAFT K. Kompella Intended Status: Proposed Standard Juniper Networks Expires: April 24, 2014 October 21, 2013 Updated processing of control flags for BGP VPLS draft-singh-l2vpn-bgp-vpls-control-flags-00 Abstract This document updates the meaning of the "control flags" fields inside the "layer2 info extended community" used for BGP-VPLS NLRI. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. 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." 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Table of Contents 1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3 2 Problem . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 3 Updated meaning of control flags in the layer2 info extended community . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4 Using p2mp LSP as transport for CW-marked VPLS frames . . . . . 4 5 Illustrative diagram . . . . . . . . . . . . . . . . . . . . . 5 6 Security Considerations . . . . . . . . . . . . . . . . . . . . 5 7 IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 8 References . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1 Normative References . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Singh, Kompella Expires April 24, 2014 [Page 2] INTERNET DRAFT Control Flags for BGP VPLS October 21, 2013 1 Introduction The use of control word (CW) helps prevent mis-ordering of IPv4 or IPv6 PW traffic over ECMP-paths/LAG-bundles. [RFC4385] describes the format for control-word that may be used over point-2-point PWs and over a VPLS. [RFC4761] describes the concepts and signaling for using BGP to bring up a VPLS. It specifies as part of its BGP VPLS NLRI that a PE may require other PEs in the same VPLS to include (or not) control-word and sequencing information in VPLS frames sent to this PE. However, [RFC4761] does not describe the behavior of PEs in a mixed environment where some PEs support control-word/sequencing and others do not. 1.1 Terminology 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 RFC 2119 [RFC2119]. 2 Problem [RFC4761] uses a VPLS BGP NLRI to specify the required behavior off multiple PEs. The behavior required off the multiple PEs identified by the NLRI indicates the VPLS label they should use in the VPLS traffic being forwarded to this PE. Additionally, by using the "control flags" it specifies whether the other PEs (in the same VPLS) should use control-word or sequenced-delivery for packets forwarded to this PE. These are respectively indicated by the C and the S bits in the "control flags" as specified in section 3.2.4 in [RFC4761]. [RFC4761] requires that if the advertising PE sets the C and S bits, the receiving PE MUST honor the same by inserting control word (CW) and by including sequence numbers respectively. However, in a BGP VPLS deployment there would often be cases where a PE receiving the VPLS BGP NLRI may not have the ability to insert a CW or include sequencing information inside PW frames. In that case the behavior of BGP VPLS needs to be further specified. This document enhances the meaning of the control flags in layer2 extended community in the BGP VPLS NLRI for an environment where not every PE in a a VPLS has the ability or the configuration to honor the control flags received from the PE advertising the BGP NLRI. Singh, Kompella Expires April 24, 2014 [Page 3] INTERNET DRAFT Control Flags for BGP VPLS October 21, 2013 3 Updated meaning of control flags in the layer2 info extended community Currently, the CW setting is not negotiated. Rather, if a PE sets the C-bit, it expects to receive VPLS packets with a control word, and will send packets the same way. If the PEs at both ends of a pseudowire don't agree on the setting of the C-bit, the PW doesn't come up. Similarly for the S-bit. This memo changes the meaning of the C-bit and the S-bit in the control flags. If a PE sets the C-bit in its NLRI, it means that the PE can send and receive packets with a control word. If the PEs at both ends of a PW set the C-bit, control words are used in both directions of the PW. If both PEs send a C-bit of 0, control words are not used on the PW. These two cases behave as before. However, if the PEs don't agree on the setting of the C-bit, control words are not used on that PW. This behavior is new; the old behavior is that the PW doesn't come up. The behavior for the S-bit is similar. 4 Using p2mp LSP as transport for CW-marked VPLS frames BGP VPLS can be used over either point-2-point LSPs acting as transport between the VPLS PEs. Alternately, BGP VPLS may also be used over p2mp LSPs with the source of the p2mp LSPs rooted at the PE advertising the VPLS BGP NLRI. In a network that uses p2mp LSPs as transport for BGP VPLS, in a given VPLS there may be some PEs that support control-word while others do not. In such a setup, a source PE that supports control- word / sequenced-delivery should setup 2 different p2mp trees - one which has as its leaves those VPLS PEs that are advertising the C/S- bits as 1, and another p2mp LSP whose leaves are PEs that are not advertising C/S-bits as 1. Singh, Kompella Expires April 24, 2014 [Page 4] INTERNET DRAFT Control Flags for BGP VPLS October 21, 2013 5 Illustrative diagram ----- / A1 \ ---- ____CE1 | / \ -------- -------- / | | | A2 CE2- / \ / PE1 \ / \ / \ / \___/ | \ ----- ---- ---PE2 | \ | | \ ----- | Service Provider Network | \ / \ | | CE5 A5 | ___ | / \ / \ / \ PE4_/ ----- PE3 / \ / |------/ \------- ------- ---- / | ---- / \/ \ / \ CE = Customer Edge Device | A3 CE3 --CE4 A4 | PE = Provider Edge Router \ / \ / ---- ---- A = Customer site n Figure 1: Example of a VPLS In the above topology, let there be a VPLS configured with the PEs as displayed. Let PE1 be the PE under consideration that is CW enabled. Let PE2 and PE3 also be CW enabled. Let PE4 not be CW enabled. PE1 will advertise a VPLS BGP NLRI, containing the C/S bits marked as 1. PE2 and PE3 on learning of NLRI from PE1, shall include the control word in VPLS frames being forwarded to PE1. However, PE4 which does not have the ability to include control-word. As per [RFC4761], PE1 would have an expectation that all other PEs forward traffic to it by including CW. However, to support the mixed-CW environment as above, PE1 will bring up the PW with PE4 despite the CW mismatch. Additionally, it will setup its data-plane such that it will strip the control-word only for those VPLS packets that are received from PEs that are themselves indicating their desire to receive CW marked packets. So, PE1 will setup its data plane to strip-off the CW only for VPLs frames received from PEs PE2 and PE3. PE1 will setup its data plane to not strip CW from frames received from PE4. 6 Security Considerations No new security issues. Singh, Kompella Expires April 24, 2014 [Page 5] INTERNET DRAFT Control Flags for BGP VPLS October 21, 2013 7 IANA Considerations None. 8 References 8.1 Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4761] Kompella, K., Y. Rekhter, Virtual Private LAN Service (VPLS) Using BGP for Auto-Discovery and Signaling, RFC 4761, January 2007. [RFC4385] Bryant, S., Swallow G., Martini L., D. McPherson, Pseudowire Emulation Edge-to-Edge (PWE3) Control Word, RFC 4385, February 2006. Authors' Addresses Ravi Singh Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US EMail: ravis@juniper.net Kireeti Kompella Juniper Networks 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US EMail: kireeti@juniper.net Singh, Kompella Expires April 24, 2014 [Page 6]