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Solving the Softwire Mesh Problem

This article discusses the softwire mesh problem and proposes a solution using L3VPN protocols and encapsulations. It explores the similarities with classic MPLS VPNs and explains the use of MP BGP for distributing routes and encapsulating packets. The solution also introduces the concept of softwire tunnels to transport AF packets across the core network.

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Solving the Softwire Mesh Problem

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  1. Solving the Softwire Mesh Problem Chris Metz, chmetz@cisco.com IETF Softwire WG Interim Meeting Hong Kong February 2006

  2. Contents • Some Terminology • Basic Problem to Solve • Similarities with L3VPN • Solution Overview • Encapsulations • BGP Protocol Elements • Examples • References

  3. Terminology (1) • AF(i) Transit Core – single AF IPv4 or IPv6 backbone network • AFBR – Address Family Border Routers, dual-stack (I,j) • AF(j) Access Islands – single AF(j) or dual-stack (i,j) access networks connected to AFBR AF = Address Family

  4. Terminology (2): What it looks like with IPv4 and IPv6 Plugged In …

  5. So what is the problem we need to solve? • Support inter-AF(j) island routing and forwarding across a single AF(i) transit core.

  6. Problem to Solve? IPv4 Islands across an IPv6 Core and …

  7. … IPv6 Islands across an IPv4 Core

  8. Some quick observations of what is needed here (1) • Multi-AF Route Distribution • ex. so that routers in AF(j) Access Island-1(including AFBR-1) learn about AF(j) prefixes located in other AF(j) access islands reachable thru AFBR-2, .. AFBR-N

  9. Some quick observations of what is needed here (2) • AF(i) Encapsulation of AF(j) Packets • ex. AFBR-1 encapsulates AF(j) packet in AF(i) “wrapper” so that packet can be forwarded across AF(i) core; wrapper is then removed at egress AFBR • also need to figure out how AFBRs agree on what “wrappers” to use and how to correlate this with the AFBR and AF(j) reachability …

  10. So big picture at this point .. • We have: • requirement to distribute multi-AF routes (IPv4 or IPv6) between AF access islands connected to a single AF backbone network • requirement to use that reachability information to forward AF packets (IPv4 or IPv6) across that backbone network from one access island network to another • requirement to encapsulate AF island-sourced IPv4 or IPv6 packets for transport across AF backbone network • This has similarities to the classic L3VPN problem and solution space. Let’s take a look …

  11. Classic MPLS VPN (1) MP-BGP = multi-protocol BGP VRF = VPN Routing/Forwarding Table • Define a new IPv4 VPN address family (VPNv4) to identify and store customer VPN IPv4 routes inside VPN routing tables (VRFs) on PE nodes • Use MP-BGP to distribute VPNv4 routes, VPN labels, Next-Hop information, etc. between PE nodes only

  12. Classic MPLS VPN (2) • Native IPv4 customer VPN packets are encapsulated in MPLS labels for transport across the MPLS backbone • IGP label(s) provide the label switched path (LSP) from PE-1 to PE-2 • VPN label identifies which destination customer site to forward IPv4 packet to

  13. Classic MPLS VPN (3) • Defined in RFC2547/RFC4364 • Many interoperable implementations and deployments • Can even support IPv6 VPNs • draft-ietf-l3vpn-bgp-ipv6-07.txt • Extended for Multicast VPN • draft-ietf-l3vpn-2547bis-mcast-01.txt • only IPv4 at the moment • Scalability • Per-PE routing table: O(# of Internet Routes + # of VPN routes for attached customers) • per-PE peering: O(# of remote PEs + # of attached customer routers) • per-local PE-to-remote PE paths: O(# of remote PEs) • Security • Discussed in RFC4111, “Security Framework for Provider-Provisioned Virtual Private Networks (PPVPNs)”

  14. Classic MPLS VPN (4) • What happens if the backbone IS NOT MPLS? Can we still do MPLS VPNs? • Yes, we can nail up inter-PE IP tunnels (e.g. GRE) and then tunnel the VPN-labeled customer packets thru or …

  15. MPLS VPN over IP (1) • Extend MP-BGP to advertise IP tunnel info along with VPNv4 prefixes, VPN labels, etc. • ex. now PE-1 learns of remote VPNv4 prefixes, the VPN labels, the next_hop and an IPv4 tunnel to use to reach that next_hop

  16. MPLS VPN over IP (2) • Native IPv4 customer VPN packets encapsulated in VPN label and IP Tunnel Header (e.g. GRE, L2TPv3, IPsec) for transport across IP backbone • Current deployments include: • static GRE tunnels between PE nodes; BGP-advertised L2TPv3 tunnel encaps

  17. Building the solution with some of these pieces … • MP-BGP • efficient and scalable one (egress AFBR) to many (ingress AFBR) delivery of multi-AF reachabililty and IP tunnel information • Standard Encapsulation Techniques • IP/IP, GRE, L2TPv3, MPLS-in-IP, IPsec, etc. • Interoperable L3VPN deployments • VPNv4 over MPLS and IP • VPNv6 over MPLS

  18. One more bit of Terminology - Softwire • Defined as a logical pt-pt (or pt-mpt) tunnel established between participating AFBR nodes • Purpose is to transport packets of AF(j) across the AF(i) backbone

  19. Solution Overview (1)Basic Idea • Leverage and reuse existing L3VPN functions and protocols where appropriate • Identify/develop a set of Softwire encapsulations using standard/existing encapsulations • Extend MP-BGP to • enable egress AFBR(s) to advertise their softwire tunnel capabilties, encapsulation parameters and preferences to participating ingress AFBR nodes … thus forming the softwire mesh • enable egress AFBR(s) to advertise AF prefixes and associated softwire(s) to use to reach those prefixes

  20. Solution Overview (2) A Picture

  21. Solution Overview (3) • AF Access Islands can be single or dual-stack • AFBR may support more than one softwire type • ex. egress AFBR-2 may support GRE and L2TPv3 encaps and will tell other AFBRs about this along with which one AFBR-2 would prefer to be used. • No new AF/SAF needed to define IPv4 and IPv6 addresses for transport in MP-BGP

  22. Solution Overview (4) • Establishment of inter-AFBR softwires is decoupled from the distribution of AF reachability information • advertise softwire tunnel encapsulation and preferences once and then many AF prefixes and which softwire tunnel to use. • more efficient BGP packing and processing by eliminating advertisement of duplicate softwire tunnel info for each prefix • enables policy control on AFBR for softwire installation and selection • Not mandated to store AF prefixes in VRFs on AFBR • only needed to support overlapping address requirement or if operator prefers this configuration

  23. Note on VRF and Global Tables • AF Island prefixes  VRFs • MP-BGP advertises as VPN:AF with VPN label, RT, etc. • AF Island prefixes  Global • MP-BGP advertises as AF • In either case: • softwire tunnels setup is separate from AF island prefix distribution • AF island prefix distribution (VPN or Global) can include softwire tunnel ID

  24. IP IPv6/IPv4 IPv6/VPN label/IPv4 - UDP/IP IPv6/UDP/IPv4 GRE IPv6/GRE/IPv4 IPv6/VPN Label/GRE/IPv4 IPsec IPv6/IPsec/IPv4 MPLS if IPv4 transit is MPLS-enabled then MPLS label may be pushed on top or replace outer IPv4 header L2TPv3 IPv6/L2TPv3/IPv4 IPv6/VPN label/L2TPv3/IPv4 IPv6/L2TPv3/IPsec/IPv4 IPv6/VPN label/L2TPv3/IPsec/IPv4 IPv6/L2TPv3/UDP/IPv4 Softwire Encapsulation Possibilities(over IPv4 Transit)

  25. IPv6 only IPv4/IPv6 IPv4/VPN label/IPv6 UDP/IP only IPv4/UDP/IPv6 GRE IPv4/GRE/IPv6 IPv4/VPN Label/GRE/IPv6 IPsec IPv4/IPsec/IPv6 MPLS if IPv6 transit is MPLS-enabled then MPLS label may be pushed on top or replace outer IPv6 header L2TPv3 IPv4/L2TPv3/IPv6 IPv4/VPN label/L2TPv3/IPv6 IPv4/L2TPv3/IPsec/IPv6 IPv4/VPN label/L2TPv3/IPsec/IPv6 IPv4/L2TPv3/UDP/IPv6 Softwire Encapsulation Possibilities(over IPv6 Transit)

  26. Quick MP-BGP NoteMP_REACH_NLRI Attribute IPv4=1, IPv6=2 Unicast=1 Multicast=2 .. .. Tunnel SAFI=64 MPLS VPN=128 http://www.iana.org/numbers.html

  27. BGP Solution Elements • Distribution of Softwire Tunnel capabilities, encapsulation(s) types, parameters and preferences • Distribution of AF Island Prefixes • Distribution of Softwire Tunnel IDs

  28. BGP Solution Elements (1a) • How does egress AFBR tell (N number of) candidate ingress AFBR(s) what softwire tunnel types, parameters and preferences it can support? • Answer: BGP Tunnel SAFI BGP RR = BGP Route Reflector

  29. BGP Solution Elements (1b)BGP Tunnel SAFI • MP_REACH_NLRI attribute with a SAFI=64 indicates tunnel attributes are present • AFI=1 and SAFI=64 point to IPv4-specific parameters • AFI=2 and SAFI=64 point to IPv6-specific parameters • NLRI of Tunnel SAFI contains address of tunnel end-point on AFBR • same address can be used by many different tunnels thus conserving address space on the AFBR that terminates the tunnel • draft-nalawade-kapoor-tunnel-safi-04.txt

  30. BGP Solution Elements (1c)Tunnel Encapsulation Attribute • Also present when Tunnel SAFI=64 are one (or more) Tunnel Encapsulation Attributes (TLVs) • egress AFBR-2 tells the peering ingress AFBR(s) (1-N) what parameters and preferences of specific encap types it can support • Defined values so far: • Type 1: L2TPv3 Tunnel information • Type 2: mGRE Tunnel information • Type 3: IPSec Tunnel information • Type 4: MPLS Tunnel information • Type 5: L2TPv3 in IPSEC Tunnel information • Type 6: mGRE in IPSEC Tunnel information • Includes a preference field that indicates the egress AFBR’s preferred ordering of softwire encapsulations that the ingress AFBR should consider when selecting a softwire tunnel. • draft-nalawade-kapoor-tunnel-safi-04.txt

  31. BGP Solution Elements (1d)Tunnel SAFI + Tunn Encapsulation Attributes 10.1.2.1 10.1.2.1 • AFBR-2 is telling the other AFBRs that • it can terminate an L2TPv3/IPv4 softwire at 10.1.2.1

  32. BGP Solution Elements (1e)After BGP Tunnel SAFI • Softwire established to AFBR-2 • it is possible to establish more than one softwire to an egress AFBR

  33. BGP Solution Elements (2) • Used existing MP-BGP protocols to distribute native or VPN-specific AF Island Prefixes between AFBR nodes

  34. BGP Solution Elements (3a) • Final piece is for egress AFBR to advertise specific tunnel identifier that ingress AFBR(s) should use to reach a particular destination AF island prefix • ingress AFBR uses this to determine which tunnel to forward packets through to reach the advertised destination • Use BGP Connector Attribute. Defined value are: • Type 1 = IPv4 address (for inter-as MDT case) • Type 2 = Tunnel ID: Tunnel End-Point Address (IPv4/6 address) • Type 3 = Tree ID: Tunnel End-Point Address (IPv4/6 address) (for multicast case) • draft-nalawade-l3vpn-bgp-connector-00.txt

  35. BGP Solution Elements (3b) • BGP AF island prefix advertisement includes connector attribute that informs ingress AFBRs which softwire tunnel to use

  36. BGP Solution Elements • BGP Updates contains Tunnel SAFI and tunnel encapsulation TLV to announce softwirecapabilities, encapsulation parameters and preferences • BGP updates include AF Island Prefix and Connector Attribute that points to softwire to use.

  37. Examples • Native IPv6 over IPv4 Core • VPNv6 over L2TPv3/IPv4 Core • VPNv4 over GRE IPv6 Core

  38. Example 1a: IPv6 over GRE/IPv4 1 64 10.1.2.1 Type 2 (GRE) 99 IPv4 10.1.2.1 GRE IPv4 GRE

  39. Example 1b: IPv6 over GRE/IPv4 3FFE:1234:1111/48 none egress AFBR tunn ID: 10.1.2.1 (type 2) glbl IPv6 glbl IPv6 3FFE:1234:1111/48 IPv4 10.1.2.1 IPv4 GRE none IPv6 IPv6 IPv6

  40. Example 2a: VPNv6 over L2TPv3/IPv4 1 64 10.1.2.1 Type 1 (L2TPv3) 99 IPv4 10.1.2.1 L2TPv3 IPv4 L2TPv3

  41. Example 2b: VPNv6 over L2TPv3/IPv4 RD:3FFE:1234:1111/48 55 egress AFBR tunn ID: 10.1.2.1 (type 2) VRF IPv6 VRF IPv6 3FFE:1234:1111/48 IPv4 10.1.2.1 IPv4 L2TPv3 55 IPv6 IPv6 IPv6

  42. Example 3a: IPv4 over GRE/IPv6 2 64 2002:1111::1 Type 2 (GRE) 99 IPv6 2002:1111::1 GRE IPv6 GRE

  43. Example 3b: IPv4 over GRE/IPv6 200.1/20 none egress AFBR tunn ID: 2002:1111::1(Type 2) GBL IPv4 GBL IPv4 200.1/20 IPv6 2002:1111::1 IPv6 GRE none IPv4 IPv4 IPv4

  44. Additional Functions • Inter-AS • advertise softwire tunnel attributes and AF reachability (to egress AFBR) across AS boundaries then … • advertise AF prefixes and connector attributes using MP-eBGP across AS boundaries • Two options for Multicast: • Traditional IPv4 or IPv6 multicast tunneled across softwire mesh • Extend mVPNv4 model to include multicast IPv6 reachability and forwarding over inclusive and selective P-multicast service interfaces (PMSI)

  45. Summarizing Key Aspects of this Solution (1) • Leverages existing and deployed L3VPN protocols (e.g. MP-BGP) and IP encapsulation techniques (e.g. GRE, L2TPv3) • Scalability: • Per-AFBR routing table: O(# of Internet Routes + # of AF island prefixes of attached islands) • per-AFBR peering: O(# of remote AFBRs + # of attached AF island routers) • per-local AFBR-to-remote AFBR paths: O(# of remote AFBRs) • Security: • RFC4111 provides framework • Control Plane: BGP/TCP MD5, BGP/TCPoIPsec • Data Plane: GRE keys, L2TPv3 cookie, IPsec • Multicast: • traditional multicast over softwire tunnels • mVPN extensions

  46. Summarizing Key Aspects of this Solution (2) • OAM • can employ existing (e.g. Netflow, interface counters per softwire) accounting mechanisms • feasible to run tunnel “health probes” (e.g. LSP Ping/VCCV/BFD) along with the usual ICMP ping/trace • Multihoming • no problem with multihoming from AF island into multiple AFBRs announcing same AF prefix • Multi-Softwire Support • AFBR can announce different softwires (e.g. GRE and L2TPv3/IPsec), a preference for one over the other and even can have specific prefixes use different softwires if desired • L2VPN • pseudowires could provide the signaling and encapsulation to transport L2-encapsulated IPv4 or IPv6 packets between AFBRs • but there is O(N2) provisioning to consider plus O(N) of L2 interfaces per AFBR

  47. In Conclusion • BGP-based VPNs (IPv4 and IPv6) as deployed and in operation today form the foundation for a softwire mesh solution • Modest extensions • support global and VRF tables • agree on set of softwire encaps and add to BGP Tunnel SAFI • support BGP Connector Attribute • Done 

  48. Question? • Currently Tunnel SAFI and Connector Attribute are not Inter-domain Routing (IDR) WG documents. Should we do the work here in Softwires or take it to IDR?Quick Note on this: Review of Paris and Vancouver IDR meeting notes implies that IDR would review and bless the encodings once some other WG (e.g. L3VPN, now softwires) figured out what application and solution and proposes encodings • References: http://www3.ietf.org/proceedings/05nov/index.html, http://www3.ietf.org/proceedings/05aug/index.html

  49. References • RFCs: • RFC2858 - Multiprotocol Extensions for BGP-4 • RFC4364 - BGP/MPLS IP Virtual Private Networks (VPNs) • RFC4023 - Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE) • Internet Drafts: • draft-ietf-l3vpn-gre-ip-2547-05, Use of PE-PE GRE or IP in BGP/MPLS IP Virtual Private Networks • draft-ietf-l3vpn-bgp-ipv6-07.txt, BGP-MPLS IP VPN extension for IPv6 VPN • draft-nalawade-kapoor-tunnel-safi-04.txt, Tunnel SAFI • draft-nalawade-l3vpn-bgp-connector-00.txt, BGP Connector Attribute • draft-townsley-l2tpv3-mpls-02.txt, Encapsulation of MPLS over Layer 2 Tunneling Protocol Version 3 (expired)

  50. Backup Notes follow …

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