mpls/ldp question

acidsatyracidsatyr Member Posts: 111
in CCIE
If i have two directly connected bgp neighbors in mpls vpn l3 scenario (and they even peer with directly connected endpoints), why is it that -mpls ip- still needs to be enabled on that link, when there are no routers inbetween?

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  • marlon23marlon23 Member Posts: 164 ■■□□□□□□□□
    because your VPNv4 prefixes carry label with them to identify VPN, even you don't need outer label to get to the next-hop, you still need inner label to identify VPN. Hence you need to encapsulate to MPLS, so need MPLS running on the interface.
    LAB: 7609-S, 7606-S, 10008, 2x 7301, 7204, 7201 + bunch of ISRs & CAT switches
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  • acidsatyracidsatyr Member Posts: 111
    marlon23 wrote: »
    because your VPNv4 prefixes carry label with them to identify VPN, even you don't need outer label to get to the next-hop, you still need inner label to identify VPN. Hence you need to encapsulate to MPLS, so need MPLS running on the interface.

    aha! got it.

    Because i thought that that's what bgp does puts the inner VPN label. In fact if i do:
    sh ip cef vrf VPN_A <some_cust_route> even without mpls enabled, cef still shows the label assigned by BGP.

    So mpls is still needed to actualy "put" that inner label on?

    Thanks so much.

    edit: is there a way for bgp to do that, so that i don't run mpls but vpnv4 are still reachable between two directly connected bgp peers?
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