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BGP VPLS Multi-homing Kireeti Kompella Bhupesh Kothari Thomas Spencer.

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Presentation on theme: "BGP VPLS Multi-homing Kireeti Kompella Bhupesh Kothari Thomas Spencer."— Presentation transcript:

1 BGP VPLS Multi-homing Kireeti Kompella Bhupesh Kothari Thomas Spencer

2 Problem Statement CE1 BGP VPLS PE1 PE2 PE3 PE4 CE1 wants resilient connectivity as a VPLS CE, so it is dual-homed to PE1 and PE2 Simple dual connectivity leads to loops and duplicate packets. One answer is to run STP on CE1 CE2 CE3

3 Solution Let PE1 and PE2 know that they are connected to the same site –Configure the VPLS VE ID to be the same Use BGP path selection to arbitrate among PE1 and PE2 as to which should be used to reach CE1 –And which forwards packets from CE1

4 Multi-homing in 4364 VPNs CE1 BGP VPN PE1 PE2 PE3 PE4 CE1 wants resilient connectivity as a VPN CE, so it is dual-homed to PE1 and PE2 Choices: pick one of PE1 or PE2 to service CE1; or use both (ECMP) 10.1/16 LP=200 LP=100 CE2 CE3

5 Differences in VPLS Cannot do ECMP: must pick one of PE1 or PE2 (say PE1), and must do so consistently from all other PEs –Both PE3 and PE4 must both choose PE1 –In particular, the losing PE (here, PE2) must know that it lost –The winning PE (here, PE1) is called the designated PE

6 Changes to BGP Path Selection 1.When are prefixes comparable? What part of the NLRI is to be compared? 2.Who wins, and how can we ensure that everyone picks consistently? Simple answer: dont use IGP metric in the tie-breaking rules 3.Control? (via Local Preference) Details in draft

7 Result 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

8 Re-homing If the designated PE fails, or if the CE- PE link breaks, the designated PE withdraws its route All other PEs (including non-designated PEs) redo path selection and pick a new designated PE Traffic is re-established via the new PE

9 Effect of Route Reflection CE1 PE1 PE2 PE3 PE4 RR If there is an RR in the path, the RR also does path selection; this can affect convergence. To get around this, use different RDs on each PE (as in 4364 VPNs) CE2 CE3

10 Status RFC 4761, section 3.5 talks about multi- homing and how to accomplish it –However, there arent enough details on how prefixes are to be compared, and how BGP path selection should be done This draft attempts to rectify this

11 Questions?


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