Multicast VPN

  1. Intra-AS mVPN
  2. Inter-AS mVPN
    1. RPF proxy vector
    2. BGP connector
  3. MVPN
    1. MCAST-VPN NLRI
    2. Intra-AS I-PMSI A-D
    3. Inter-AS I-PMSI A-D
    4. S-PMSI A-D / Source Active A-D
    5. C-multicast route
    6. Leaf A-D
    7. PMSI Tunnel

Intra-AS mVPN

  • MDT – multicast distribution tree, built by PE for every mcast domain
  • MDT extended community:
    • type 0x0009, RD = type 2
    • ASN + root address + MDT group
    • sent in Update on creating default MDT
    • on receive – SSM join, no import into VRF
    • for older IOS
  • SAFI = 66 (newer IOS)
  • P router: mcast entries only in global RIB
  • CE router PIM neighborship only with PE
  • mcast state in core does not depend on mcast state in client VRFs
  • VRF mcast groups are mapped to a single mcast group in the core
  • GRE encapsulation, IP multicast in core, no labels
  • PIM SM, SSM
  • RPF: if mcast prefix is received via BGP, then RPF interface = MTI (BGP next-hop ≡ PIM neighbor)
  • multicast tunnel interface (MTI)
    • distributes mcast info
    • RPF check
    • PIM SD mode
    • inherits parameters from BGP interface (mcast enabled)
  • MDT
    1. default:
      • transports control plane traffic (always)
      • transports low-bandwidth traffic to all PEs
      • all PEs join, even if there are no listener/streamer (SSM)
      • immediate SPT switchover, every PE is a root for its tree (threshold = infinity|BiDir)
      • ToS of C-packets is copied to ToS of P-packets
    2. data:
      • transports high-bandwidth traffic to subscribed PEs
      • dynamically created from mcast group pool once threshold is exceeded
      • threshold is checked per stream ((S,G), not (*,G))
      • messages:
        1. Data-MDT join:
          • passed within default MDT on creating data MDT
          • VPN source, VPN group, Data-MDT group
          • 224.0.0.13, UDP 3232
          • PE waits for a while before switching to data MDT
          • if no listeners present, PEs cache the message
      • timers:
        1. data MDT:
          • 1 min default
          • sending data MDT join
        2. MDT delay:
          • 3s default
          • delay before switching to data MDT
(config)# ip pim vrf <NAME> ...
(config)# ip msdp vrf <NAME> ...
(config)# ip multicast-routing vrf <NAME> ...

; use another VRF RIB for RPF
(config)# ip mroute vrf <NAME> <mrange> fallback-lookup global | vrf <SRC>

; restrict mgroup for fallback-lookup
(config)# ip multicast vrf <NAME> rpf select vrf <SRC> group-list <ACL>
(config)# interface loopback 0

; PIM has to be enabled on BGP source interface
(config-if)# ip pim sparse 
(config-vrf)# mdt default <default group>

; ACL limits (S,G) that can use data MDT; enough on source PE only; on overflow – reuse addresses
(config-vrf)# mdt data <group> <mask> threshold <kbps> [list <ACL>]
; default MDT; send – data MDT
# show ip pim mdt <receive|send>
# show ip pim vrf <NAME>
# show ip msdp vrf <NAME>
# show ip igmp vrf <NAME>

Inter-AS mVPN

  • elements:
    1. MDT SAFI (older IOS used RD type 2 and extcommunity)
    2. BGP connector
    3. RPF proxy vector (PIM extension)
  • BGP-free core: Ps do not know addresses of PEs from other AS
  • MDT SAFI
    • 66
    • MP_NLRI = RD:PE_IPv4 addr:MDT group addr (PE_IPv4 – BGP peer address)
    • MP_NEXT_HOP = BGP peer IPv4 address (does not have to match PE address – bgp next-hop)
  • PIM SSM
  • VPN mcast traffic is transported within MDT
  • PE discovery for SSM – BGP autodiscovery (BGP-AD)
  • PIM is used to build MDT tunnels between PEs in different AS

RPF proxy vector

  • PIM TLV, contains IPv4 address of proxy for RPF check and PIM Join (ASBR within AS)
  • PIM Joins are sent to PE IPv4 address (de jure); TLV is added to next-hop so Joins are sent towards next-hop proxy ASBR (de facto)
  • PIM TLV is removed only by proxy ASBR
  • tradeoff: number of states for mcast RIB on P ≈ PE * mVPN

BGP connector

  • transitive optional
  • contains IPv4 PE from other AS
  • along with VPNv4 prefixes on advertising PE
  • required for inter-AS RPF check: packet is received from PE address but RPF prefix is known via ASBR – would result in RPF fail
  • C-PIM uses for RPF check and PIM Join next-hop

Without BGP connector R1 would check RPF via R3 when packet would be received from R5 – fail.

Without PIM Proxy Vector R2 does not know about R5 = cannot send Join further – fail.

PE1B in MDT – address used to source BGP updates.

BGP Connector preserves next-hop address of PE1B.

MDT SAFI → group, next-hop, proxy vector

Source ← BGP Connector 

; on PE, use proxy for MDT in VRF
(config)# ip multicast vrf <NAME> rpf proxy rd vector

; on P or ASBR
(config)# ip multicast rpf proxy vector

(config)# ip pim ssm default
; exchange MDT SAFI, discover mcast PE for SSM (BGP-AD)
(config-router)# address-family ipv4 mdt

; mcast BGP: in case unicast/mcast paths differ
(config-router)# address-family ipv4 multicast

(config-router-af)# neighbor <IP> next-hop-self 
# show ip pim mdt [bgp]
# show ip mroute <group> proxy

MVPN

  • SAFI = 129, RFC 6514
  • uses BGP to exchange active src, default/data MDT instead of PIM
  • uses MCAST-VPN NLRI (27), PMSI Tunnel (23)
  • I-PMSI ≡ default MDT, S-PMSI ≡ data MDT
  • MPSI NLRI include Tunnel attributes
  • on receiving source tree Join while using PIM-SM, PE sends source active A-D because (S,G) is created if PE is RP
  • each site has its own RP, exchange sources via RT5 ⇒ MSDP not needed
  • I-PMSI = inclusive P-multicast service interface
  • S-PMSI = selective P-multicast service interface

MCAST-VPN NLRI

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Route type   |     Length    |                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+              Data             /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Route type:

  • 1 = Intra-AS I-PMSI A-D
  • 2 = Inter-AS I-PMSI A-D
  • 3 = S-PMSI A-D
  • 4 = Leaf A-D
  • 5 = source active A-D
  • C-multicast:
    • 6 = shared tree join
    • 7 = source tree join

Intra-AS I-PMSI A-D

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              RD                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Originating IP                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

All PEs

Inter-AS I-PMSI A-D

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              RD                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Source AS                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

All ASBR

S-PMSI A-D / Source Active A-D

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              RD                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Source AS                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mcast src len |                                               \
+-+-+-+-+-+-+-+-+           Multicast source address            /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mcast grp len |                                               \
+-+-+-+-+-+-+-+-+           Multicast group address             /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Originating IP                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Originating IP: only for S-PMSI A-D
S-PMSI: PE data-MDT signalling
Source Active: customer source announcement (PIM-SM)

C-multicast route

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                              RD                               |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                           Source AS                           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mcast src len |                                               \
+-+-+-+-+-+-+-+-+           Multicast source address            /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mcast grp len |                                               \
+-+-+-+-+-+-+-+-+           Multicast group address             /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

On receiving PIM Join

Leaf A-D

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                           Route key                           /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Originating IP                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

In reply to S-PMSI A-D

PMSI Tunnel

 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
                                                +-+-+-+-+-+-+-+-+
                                                |   Reserved  |L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Tunnel type  |                  MPLS label                   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\                                                               \
/                           Tunnel ID                           /
\                                                               \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

L: 1 = leaf info required

Types:

  • 0 = no tunnel info present
  • 1 = RSVP-TE P2MP LSP
  • 2 = mLDP P2MP LSP
  • 3 = PIM-SSM
  • 4 = PIM-SM
  • 5 = PIM-BD
  • 6 = ingress replication
  • 7 = mLDP MP2MP LSP