BGP based Multi-homing in Virtual Private LAN Service

Wim Henderickx

Florin Balus

Problem Statement

CE1 VPLS

PE1

PE2

PE3

PE4

CE1 is multi-homed to PE1 and PE2; CE1 wants a resilient connectivity

Simple dual connectivity leads to loops and duplicate packets. Proposal provides a complementary solution next to STP, MC-LAG, etc leveraging BGP

CE3

CE4

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

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

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

Proposal• BGP AD MH NLRI to carry the VSI-ID

identifying the base VSI and 2 byte Site ID 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

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length (2B) (=14) | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | Route-distinguisher (RD) (8B) | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | VSI-ID (HO bits) (2B) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VSI-ID (LO bits) (2B) | Site ID (2B) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Operation

CE2

VPLS

PE1

PE2

PE3

PE4

Site1LPREF=200

CE3

CE4

CE1

Site2LPREF=200

Site1LPREF=100

Site2LPREF=100

PE1 is elected as designated forwarder

Operation: link failure

CE2

VPLS

PE1

PE2

PE3

PE4

Site1LPREF=200

CE3

CE4

CE1

Site2LPREF=200

Site1LPREF=100

Site2LPREF=100

PE1 withdraws the MH NLRI, send a MAC flushPE2 becomes designated forwarder for CE1

Operation: PE failure

CE2

VPLS

PE1

PE2

PE3

PE4

Site1LPREF=200

CE3

CE4

CE1

Site2LPREF=200

Site1LPREF=100

Site2LPREF=100

PE2 becomes designated forwarder for CE1/CE2 upon BGP neighbor failure detection or upon reception of MH-NLRI

withdraw for CE1/CE2

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

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?

Questions?