1. Multicast Signaling using BGP
IETF 64 Nov 2005
Gargi Nalawade
Nidhi Bhaskar
Pranav Mehta

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 - {RD:G:Flags:S/RP:U-PE:D-PE}
Flags : RPT Bit, WC Bit
D-PE Optional, Label Optional.
Update from D-PE to U-PE :
RD:G:Flags:S/RP:U-PE:D-PE
Update from U-PE:
RD:G:Flags:S/RP:U-PE, Inner-Label
Tunnel Identifier carried as Attribute

5. Transit for VPN SSM - BGP
BGP Update:
RD: :SPT: :PE-4:PE-2
BGP Update:
RD: :SPT: :PE-4:PE-2 RR
PE-1
PIM-V4 VRF JOIN: , e0 e1
PIM-V4 VRF JOIN: ,
BGP Update:
RD: :SPT: :PE-4
Label=200, FEC=FEC200
PE-2
CE-2
Receiver1
PE-4
CE-4
Source =
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-PE’s RD.

7. BGP- Issue w/ Re-using unicast RTs
PE-2
Red VRF: RD2
Import RT: RT1
Export RT: RT2
Blue VRF: RD3
Import RT:RT1
Export RT:RT3 P
PE-1
Red VRF: RD1
Import RT:RT2
Export RT:RT1 e0 e1
PE-2
CE-Y
Source=
PE-1
CE-X
Host =
PE-3 e0
PE-2 Unicast imports reachability for into Red and Blue VRF.
When host joins towards >We don’t want join imported into both Red and Blue table.
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.
RD:Flags:G/mask:RP

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:
PE1:G:SSM:S:ASBR1
Update Sent to ASBR1:
ASBR1:G:SSM:S:Label100:FEC-Y
Update sent to ASBR2:
ASBR2:G:SSM:S:PE2
Update sent to PE2:
ASBR2:G:SSM:S:Label20:FEC-X
vpnv4 RD:S
NH=PE1
vpnv4 RD:S
NH=ASBR1
ASBR2 Update to ASBR1:
ASBR1:G:SSM:S:ASBR2:Label10
vpnv4 RD:S
NH=ASBR2
ASBR1
ASBR2
PE1
AS 2
PE2
AS 1
next-hop-self towards iBGP neighbors
CE1
CE2
CE3
CE4 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 N*NLRI 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