For inter-AS or intra-AS MVPN, the root PE (the PE on which the source resides) loopback IP address is usually not advertised into each AS or area. As such, the P routers in the ASs or areas that the root PE is not part of are not able to resolve the root PE loopback IP address. To resolve this issue, the leaf PE, which has visibility of the root PE loopback IP address using BGP, creates a recursive opaque with an outer root address of the local ASBR or ABR and an inner recursive opaque of the actual root PE.
Some non-Nokia routers do not support recursive opaque FEC when the root node loopback IP address is resolved using IBGP or EBGP. These routers accept and generate a basic opaque type. In such cases, there should not be any P routers between a leaf PE and ASBR or ABR, or any P routers between ASBR or ABR and the upstream ASBR or ABR. Figure: Example AS shows an example of this situation.
In Figure: Example AS, the leaf HL1 is directly attached to ABR HL2, and ABR HL2 is directly attached to ABR HL3. In this case, it is possible to generate a non-recursive opaque simply because there is no P router that cannot resolve the root PE loopback IP address in between any of the elements. All elements are BGP-speaking and have received the root PE loopback IP address via IBGP or EBGP.
In addition, SR OS does not generate a recursive FEC. The global generate-basic-fec-only command disables recursive opaque FEC generation when the provider needs basic opaque FEC generation on the node. In Figure: Example AS, the basic non-recursive FEC is generated even if the root node HL6 is resolved via BGP (IBGP or EBGP).
Currently, when the root node HL6 systemIP is resolved via BGP, a recursive FEC is generated by the leaf node HL1:
When the generate-basic-fec-only command is enabled on the leaf node or any ABR, they generate a basic non-recursive FEC:
When this FEC arrives at HL2, if the generate-basic-fec-only command is enabled then HL2 generates the following FEC:
If there are any P routers between the leaf node and an ASBR or ABR, or any P routers between ASBRs or ABRs that do not have the root node (HL6) in their RTM, then this type 1 opaque FEC is not resolved and forwarded upstream, and the solution fails.