1. BGP based Multi-homing in Virtual Private LAN Service
Wim Henderickx
Florin Balus

2. Problem Statement CE3 PE3 PE1 VPLS CE1 PE2 PE4 CE4
CE1 is multi-homed to PE1 and PE2; CE1 wants a resilient connectivity
CE3
VPLS
PE3
PE1
CE1
PE2
PE4
CE4
Simple dual connectivity leads to loops and duplicate packets. Proposal provides a complementary solution next to STP, MC-LAG, etc leveraging BGP

3. Goal Address both PE and access link failure
Provides fast convergence times
Only the traffic transiting the affected network elements should be impacted
Decouple the Multi-Homing mechanism from the PW signaling
Minimize the traffic load on the network; ideally just the local PEs should be involved in the selection process
Re-use existing BGP procedures while minimizing the network migration to ease operation

4. Solution
Let PE1 and PE2 know that they are connected to the same site using BGP-AD AFI/SAFI, procedures
Add to BGP-AD NLRI an identifier for the Multi-homed Site
Site ID to be the same between peer PEs
PW infrastructure can be built using either LDP or BGP signaling
Local Multi-homed PE(s) decide which PE is the designated forwarder for a given site/CE using BGP attributes
LPREF e.g.
VSI ID is the tie-breaker
If none of the attached CE(s) is elected as designated forwarder for a given VSI, PW status can be used to minimize the BUM traffic in the network

5. Solution Designated PE forwards packets from and to CE
Non-designated PEs (losing PEs) drop packets from CE as well as from other PEs
The effect is as if CE was single-homed to just the designated PE

6. Proposal
BGP AD MH NLRI to carry the VSI-ID identifying the base VSI and 2 byte Site ID

7. PE1 is elected as designated forwarder
Operation
Site1 LPREF=200
Site2 LPREF=200
CE3
PE3
VPLS
CE1
PE1
CE2
PE2
PE4
CE4
Site1 LPREF=100
Site2 LPREF=100
PE1 is elected as designated forwarder

8. Operation: link failure
Site1 LPREF=200
Site2 LPREF=200
CE3
PE3
VPLS
CE1
PE1
CE2
PE2
PE4
CE4
Site1 LPREF=100
Site2 LPREF=100
PE1 withdraws the MH NLRI, send a MAC flush PE2 becomes designated forwarder for CE1

9. Operation: PE failure CE3 PE3 CE1 PE1 VPLS CE2 PE2 PE4 CE4
Site1 LPREF=200
Site2 LPREF=200
CE3
PE3
VPLS
CE1
PE1
CE2
PE2
PE4
CE4
Site1 LPREF=100
Site2 LPREF=100
PE2 becomes designated forwarder for CE1/CE2 upon BGP neighbor failure detection or upon reception of MH-NLRI withdraw for CE1/CE2

10. Operation continued
RR usage does not impact the operation since the VSI-ID is unique
No impact in Inter-AS scenario’s since the designated forwarding decisions are local multi-homed PE(s)
No impact on H-VPLS operation

11. Next steps Minimize BGP flooding through the usage of ORF
Add startup procedures and procedures for re-configuration
Do we use this framework for both LDP VPLS and BGP VPLS?

12. Questions?