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  • 1.  L2VPN Inter-AS with Option B and ASBR acting as a PE

    Posted 04-05-2022 11:13
      |   view attached

    Hello Team!

     

    We have replicated a client setup where L3 VPN inter-as option B was implemented and on top of that, they want to enable L2vpn services.

    Before implementing they tested the l2vpn with ASBR as a PE, unfortunately, the l2vpn was not coming up, when configuring the l2vpn over option B with another device as PE (Not ASBR) the l2vpn started to work.

     

    I have replicated the same issue and also I have a workaround for this, lab diagram is attached to the email.

    In this setup ASBR2 is acting both ASBR and PE, between ASBRs there is a BGP LU session. The following were observed:

    • With eBGP LU and l2vpn signalling as AF, the l2vpn is not coming up.

     

    • If LDP is configured between ASBR1 and ASBR2 end eBGP is established between lo0.0 with multihop, the l2vpn comes up and ASBR2 know to push label received over BGP-LU and l2vpn is working.

     

    We are looking for a solution that would not involve LDP between ASBRs, is there any knob available that we are not aware of? Based on our observation the l2vpn on ASBR2 is looking into inet.3 to find a LSP to the remote PE, but if ASBR is also PE we have BGP-LU and there is no need to run LDP/RSVP. If there is no entry in inet.3 for ASBR1 lo0 l2vpn simply does not come up.

     

    Thank you for looking into this!



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    Alin Bandiu
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  • 2.  RE: L2VPN Inter-AS with Option B and ASBR acting as a PE

    Posted 05-02-2022 03:32
    Hi, 

    I got this working, for anyone who may face this problem here is the solution: 

    -> 2 BGP sessions between ASBRS 
    -> 1 BGP session will be between lo0 and others via directly connected links 
    -> The directly connected session will care lo0 addresses and will serve as underlay connectivity for the second bgp session ( via lo0) also it will be BGP-LU with inet labelled-unicast rib inet.3, so the lo0 route will be installed in inet.3 table 
    -> The lo0 session will care just inet-vpn / l2vpn routes 
    -> The lo0 routes will be copied using rib-groups from inet.3 to inet.0 
    -> Because we have lo0 routes in inet.3 L2VPN check pass now ( it needed an LSP to the remote PE which is ASBR1 lo0 address) 

    And this is how L2vpn is working when ASBR is also a PE



    ------------------------------
    Alin Bandiu
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