Routing

BGP unicast routes must advertise to the VRF Route Import Ext Community, identifying the root PE, for the feature to operate properly. Failure to do so results in PIM Inter-AS joins being dropped.

The community is an address-based community where the global administrator field is the address of the root PE and local administrator field is set to 0 (GRT). No new configuration is required; however, an operator must enable inter-AS VPN and configure export policy to ensure the community is added to the BGP routes as required. The BGP unicast route is propagated across the AS, as shown in Figure: In-band signaling with non-segmented inter-AS MLDP trees in GRT (the same processing, not shown, applies to a BGP route specifying address used to build mLDP tree rooted at ROOT-1). The following configuration example shows an export policy configuration.

policy-options
        — begin
        — community "A" members "target:1.1.1.1:0"
        — community "B" members "ext:010b:0a1401060000"
            — policy-statement "fromlocal"
                — entry 10
                    — from
                        — protocol direct
                    — exit
                    — to
                        — protocol bgp
                    — exit
                    — action accept
                        — community add "A" "B"
                    — exit
                — exit
                — default-action reject
        — exit
        — policy-statement "accept_all"
            — default-action accept
            — exit
        — exit
        — commit
    exit
    bgp
    …
        — enable-inter-as-vpn
        — …
        — export "fromlocal" "accept_all"
        — …
        —  no shutdown
    exit

Static routes must be configured on inter-ASBR LDP-enabled links because the BGP peer uses a host address from the local subnet of the links (for GRT and VPN option C), or the BGP peer uses a system IP address that is not in the base routing table (for VPN option B).

• For system-IP to system-IP, static-routes are required for bringing up the EBGP/LDP session.

• If the link IP is used for creation of EBGP and ILD, then static-routes are not required; however, static-route (host-route) is mandatory on ASBR2 for the resolution of MLDP FEC, as the link LSR ID is not resolved by LDP using a /24 route; it needs a /32 route.