Multicast Signaling using BGP

1
Multicast Signaling using BGP

• IETF 64 Nov 2005
• Gargi Nalawade gargi_at_cisco.com
• Nidhi Bhaskar nidhi_at_cisco.com
• Pranav Mehta pmehta_at_cisco.com

2
PE-PE signaling for Multicast VPNs

• Multicast VPN PE-PE signaling exists with PIM LAN
  procedures
• Push for having the PE-PE signaling for non-LAN
  based approach
• Latter requires procedures for PIM Join/Prune,
  binding (among other things)
• Push for using BGP for the purpose
• Aim to describe the required protocol changes and
  analyze the impact on BGP/PIM

3
Enhancements required in BGP

• Multicast PE-PE (Overlay) SAFI
• RT/RD Import/Export
• Filtering
• PIM/BGP Interaction
• Inter-AS
• No extensions for Unicast Reachability. Rely
  on existing VPNv4 Unicast for that.

4
New SAFI Multicast Overlay SAFI

• NLRI - RDGFlagsS/RPU-PED-PE
• Flags RPT Bit, WC Bit
• D-PE Optional, Label Optional.
• Update from D-PE to U-PE
• RDGFlagsS/RPU-PED-PE
• Update from U-PE
• RDGFlagsS/RPU-PE, Inner-Label
• Tunnel Identifier carried as Attribute

5
Transit for VPN SSM - BGP
BGP Update RD232.1.1.1SPT1.1.1.1PE-4PE-2
BGP Update RD232.1.1.1SPT1.1.1.1PE-4PE-2
RR
PE-1
PIM-V4 VRF JOIN1.1.1.1, 232.1.1.1
e0
e1
BGP Update RD232.1.1.1SPT1.1.1.1PE-4 Label20
0, FECFEC200
PIM-V4 VRF JOIN1.1.1.1, 232.1.1.1
PE-2
PE-4
PE-3
e0
CE-3
Receiver2
6
Route-Targets/RD

• RTs are carried as in Unicast VPNv4.
• Cleaner to define new RTs for multicast.
• RD, traditionally multicast uses U-PEs RD.

7
BGP- Issue w/ Re-using unicast RTs
PE-2 Red VRF RD2 Import RT RT1 Export RT
RT2 Blue VRF RD3 Import RTRT1 Export RTRT3
P
PE-1 Red VRF RD1 Import RTRT2 Export RTRT1
e0
e1
PE-2
PE-1
PE-3
e0
CE-Z
Receiver2
8
BGP - Filtering

• Attach U-PE as Attribute for filtering J/P NLRI.
• Or Assign an RT per upstream PE
• Use ORF/RT-Constrain to filter Tunnel Binding/RP
  Mappings.
• Filtering further to keep binding state only
  along multicast tree is not specified.

9
PIM/BGP Interaction

• PIM Join or Prune is not part of NLRI.
• S/RP,G Join is NLRI MP_REACH.
• S/RP,G Prune is NLRI MP_UNREACH.
• S,G,RPT Prune is NLRI MP_REACH.
• S,G,RPT Join is NLRI MP_UNREACH
• PIM Mode is not encoded in NLRI.
• RP Mappings carried via separate BGP SAFI.
• Can combine into same SAFI if necessary.
• RDFlagsG/maskRP

10
BGP Inter-AS

• Multicast specific aggregation. No need to
  carry forward tracked downstream PEs from one AS
  to another.
• RPF lookup to find Upstream ASBR.
• Tunnel/Binding information updated at ASBR.

11
ABSR Exchange VPNv4 Routes - Option B
Update Sent to PE1 PE1GSSMSASBR1 Update Sent
to ASBR1 ASBR1GSSMSLabel100FEC-Y
Update sent to ASBR2 ASBR2GSSMSPE2 Update
sent to PE2 ASBR2GSSMSLabel20FEC-X
vpnv4 RDS NHPE1
vpnv4 RDS NHASBR1
ASBR2 Update to ASBR1 ASBR1GSSMSASBR2Label1
0
vpnv4 RDS NHASBR2
ASBR1
ASBR2
PE1
AS 2
PE2
AS 1
next-hop-self towards iBGP neighbors
CE1
CE4
CE2
CE3
S
12
BGP Futures/Open Issues

• BGP will not restrict Binding state to multicast
  tree.
• New functions in BGP like aggregating D-PE, U-PE
  based filtering, RPF lookup on ASBR and probably
  others.
• Not enough bits to encode SAFI length for IPv6!!
• RR Stores 1 multicast route as NNLRI where N is
  of D-PEs interested in stream.
• Some PIM updates are full-state. Will need
  careful mapping of PIM states to BGP updates and
  state machine.
• Need better understanding of the number of
  multicast streams and the rate at which they
  churn.
• Extensions to support Bidir-PIM/BSR, PIM Asserts