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513 Views 1 Reply Latest reply: Apr 12, 2012 8:07 AM by Mohit Kansal CCIE RS RSS

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MPLS Requirements

Apr 12, 2012 4:39 AM

bporcelli76 2 posts since
Jun 6, 2009

For quite sometime, I can remember that there was this requirement for MPLS to have the "VPNv4 peering interfrace prefix MUST be /32" and it was documented as such.  Is this still the case, because I just tested the theory out and specifically made sure that my vpnv4 peerings were done off loopbacks were I didn't have the as /32 and my PE-to-CE routing works fine over the mpls cloud.


Any feedback would be great, because i don't know what's right or wrong now.

  • Mohit Kansal  CCIE RS 111 posts since
    Feb 12, 2009
    Currently Being Moderated
    1. Apr 12, 2012 8:07 AM (in response to bporcelli76)
    Re: MPLS Requirements

    I also have seen many documents with the same concept of /32 loopback. But this is just to avoid wastage of addresses and secondly to make sure PE routers have reachibility to each other over MPLS LSP.


    Here is a case in which it is preferred to go with /32 loopback


    I am using OPSF as IGP and loopback of /24.

    OSPF will advertise the loopback address of PE to other routers as /32 network. Middle P routers will install these routes in routing table as /32 and will put them in LFIB also. But, what the issue is P router will not receive any label for this /32 network from PE router because if you check routing table on PE, there will be route for only /24 and will generate label also for /24 not for /32.


    This will break the LSP and all the VPN traffic will get dropped.



    Mohit Kansal

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