MVPN Update

1
MVPN Update

• New version of bgp encoding draft
• BGP update syntax and semantics reworked to
  reflect current thinking
• Inter-AS proposal fleshed out in detail
• Arch. draft not yet updated, to be done shortly
• This presentation will discuss
• Changes from last rev
• Selected interesting topics
• Remaining open issues

2
BGP Attributes for Unicast VPN-IPv4 Routes

• Extended communities to identify
• AS of origin
• VRF of origin (including PE of origin)
• These are used for RPF Lookup when PE received
  C-Join from a CE
• Root IPv4 address looked up in VRF
• Get source AS for inter-AS trees (later)
• Get address of upstream PE

3
MCAST-VPN Address Family

• One AF, but multiple route types
• C-Multicast (C-M) Routes convey customer
  multicast routes (from within a VPN)
• Auto-Discovery (A/D) Routes convey information to
  set up MVPN infrastructure in the backbone
• Find other PEs and /or ASes of a given MVPN
• Bind MVPN to default PMSI (I-PMSI)
• Bind individual streams to S-PMSI
• Bind PMSI to tunnel
• A few other uses having to do with P-tunnel setup
  and/or binding of multicast streams to P-tunnels

4
Intra-AS A/D Routes for Auto-Discovery

• NLRI
• RD of originating VRF
• IP address of originating router
• Attributes
• RTs controlling route distribution
• PMSI tunnel attribute, identifying default I-PMSI
  mechanism
• Enough info to set up receiver-initiated join
  type tunnels
• Other tunnel types may require additional
  BGP-based protocol based on leaf a/d routes
• For aggregate trees, upstream-assigned MPLS label
  specified
• N.B. Two intra-AS A/D routes are never comparable

5
Other Uses of Intra-AS A/D Routes

• Bind ltS,Ggt to an S-PMSI
• Include ltS,Ggt in the NLRI
• Without ltS,Ggt binding applies to entire MVPN
• Active Source Advertisement (for PE as RP
  schemes)
• Include ltS,Ggt in NLRI
• Omit PMSI Tunnel Attribute

6
C-M Routes

• Types
• Source tree join
• Shared tree join
• Prune source off shared tree
• Route type is part of NLRI
• Different route types never comparable
• Claim
• with these route types, all PIM operations can be
  represented by BGP updates or withdraws

7
C-M Routes

• NLRI
• Reverse RD
• RD from the VPN-IPv4 address of the root of this
  C-tree
• Slightly different procedure used for inter-AS
• /32 Source (omitted in shared tree joins)
• /32 Group
• Attributes
• RTs to control route distribution
• Route Import target, identifying a particular PE
  as the upstream PE

8
No Originating PE in C-M Routes

• Different PEs joining same C-tree generate
  comparable routes
• RRs and ASBRs install and redistribute just one
  such
• Upstream PE or ASBR sees 1 join per C-tree,
  need not do explicit tracking of receiving PEs
  (unless needed for P-tunnel type)
• RR is leveraged to allow PEs get effect of join
  suppression, without need to do join caching and
  prune override
• Control plane allows NBMA procedures which have
  some aspects of PIM LAN procedures and some
  aspects of PIM P2P procedures.

9
Inter-AS

• Inter-AS Tunnel rooted at the source AS
• Other ASs are nodes on this inter-AS tunnel
• Inter-AS Tunnel comprises segments
• AS-AS tunnel segments that connect ASs together
  on the inter-AS tunnel
• Intra-AS tunnel segment used by an AS to deliver
  traffic to PEs/ASBRs within an AS on the inter-AS
  tunnel
• Distinct from intra-AS trees
• A PE/ASBR receives traffic on a single intra-AS
  segment or AS-AS segment of the inter-AS tunnel

10
Inter-AS MVPN Auto-Discovery

• Inter-AS Auto-discovery routes
• granularity of ltSource AS, MVPNgt
• advertised by ASBRs
• Aggregate intra-AS Auto-discovery information
  with granularity of ltPE, MVPNgt
• AS specific RD
• All ASBRs within an AS configured with same AS
  specific RD
• Propagation of Inter-AS Auto-discovery routes
  from the source AS to other ASs leads to the
  creation of the inter-AS tunnel

11
Inter-AS Tunnel Creation

• Inter-AS tunnels constructed by stitching tunnel
  segments
• intra-AS tunnel segments stitched with AS-AS
  tunnel segments
• Independent P-Tunneling technology per AS
• MVPN that is present in N ASes would result in N
  inter-AS P-tunnels (one per AS, not one per PE)
• To improve scalability multiple intra-AS tunnel
  segments within an AS could be aggregated into a
  single intra-AS P-tunnel using upstream labels

12
Inter-AS Tunnel CreationIntra-AS Segment

• No intra-AS segment in source AS
• In other ASes, intra-AS segment is triggered when
  an ASBR receives an ltAS, MVPNgt A/D route from an
  EBGP neighbor
• ASBR readvertises this route in IBGP
• Also carries the intra-AS tunnel segment if the
  ASBR does not need to know the leaves ELSE
• Intra-AS Tunnel segment is advertised after
  learning the leaves
• Other PEs/ASBRs are free to pick different
  upstream ASBRs
• Join the respective intra-AS tunnel segment
• Originate leaf AD routes if the upstream ASBR
  needs to learn the leaves

13
Inter-AS Tunnel CreationAS-AS Segment

• Interconnect adjacent ASBRs on the Inter-AS
  Tunnel
• When an ASBR receives an ltAS, MVPNgt route from an
  EBGP peer it sends back a leaf A/D route
• Carries a downstream assigned MPLS label
• Tunnel segment identifier set to ingress
  replication

14
Inter-AS C-M Routing Exchange

• MVPN PE-PE C-M Routing Exchange
• Aggregation of MVPN Routing Information
• Granularity of ltAS, C-S/C-RP, C-Ggt
• Inter-AS MVPN C-M Routing Info is propagated by
  egress PE towards the source AS and the source PE
• Propagates using the reverse path of the inter-AS
  auto-discovery routes, i.e. ltsource AS, MVPNgt
  route
• No flooding
• No Receiver (S, G) state in the ASBR forwarding
  plane

15
Inter-AS

• Control plane exchange between ASes only at ASBRs
  or RRs
• Use RT Constrain to limit distribution of
  auto-discovery routes and C-M routes
• Support of all three options for inter-AS unicast

16
Topics Shared Tree State

• join(,G) and prune(S,G,R)
• PIM sends single message saying I want to join
  (,G), but not for sources S1, S2, S3
• BGP handles these as 4 separate routes (not
  necessarily 4 separate updates)
• The BGP-to-PIM state machine has some massaging
  to do
• For a given G, PIM needs to react to the complete
  set of BGP join(,G) and prune(S,G,R) states
• Not 1-1 corresp. between PIM BGP messages

17
What Replaces PIM Asserts

• If C-S multi-homed to several PEs in same AS,
  force all PEs to choose same upstream PE for
  given C-S
• absolutely required for segments of inter-AS tree
• presupposes different RD at each PE
• selection not based on BGP-installed route
• Discard data on C-S tree if received on tunnel
  from wrong upstream PE and/or tunnel
• If a PE receives from both (C-,C-G) and
  (C-S,C-G), need more
• Force all PEs to join C-S tree (using leaf a/d
  routes)

18
C-Protocols that use Flooding

• BSR and other flooding-based protocols
• Require default MI-PMSI
• treat as data sent over default MI-PMSI
• do not try to absorb into BGP control plane

19
PEs, RPs, and MSDP

• Goal
• Enable removal of PIM-SM complexity in backbone
• No shared trees among sites
• No switching from shared trees, no pruning
  sources from shared trees, etc.
• Less control plane overhead, less state
• More stable traffic pattern in backbone
• But dont require each PE to be an RP
• Proposal
• PE runs MSDP with local RPs
• PEs use BGP to advertise active sources
• Intermediate between fully transparent and
  outsource your RPs

20
Dampening C-M Routes

• PE multicast routing rate of change is not
  directly proportional to terminal behavior
• After the first (S,G) Join, subsequent Joins for
  same (S,G) do not cause backbone signaling
• PE multicast routing rate of change depends on
  application
• Still, PEs may have to support a high rate of C-M
  route changes, causing PE-PE protocol load
• C-M route dampening is a possible solution
• Principle waiting before propagating a C-M
  routing change
• Timers may increase with a backoff algorithm
• May it hurt latency ? Only in some cases (see
  next slide)

21
Dampening C-M Routes

• Dampening C-M ''prunes''
• Won't increase leave-latency perceived by the CE
  or end user
• Can be done aggressively
• Dampening C-M joins only hurts the first join
  in the MVPN
• Where to dampen?
• on the receiver-side PE, before propagating
• on a route reflector

22
Future Work

• Carriers Carrier
• Details for support of Bidir C-trees
• DF forwarder election
• Use of MP2MP LSPs as P-tunnels for intra-AS
  tunnels and intra-AS segments of inter-AS tunnels
• BGP on the CE-PE link for multicast routes?
• not transparent, but no worse than for unicast