Inter-AS model C (RFC 4364 option C) only requires that each autonomous system have a transport MPLS tunnel of some sort (LDP, RSVP-TE, or SR). LDP itself is therefore optional.

What is mandatory is:

• inside each AS, VPN-IPv4/-IPv6 routes are carried by MP-iBGP (normally PE–RR or PE–PE);

• between ASBRs the labeled VPN routes are exchanged with MP-eBGP;

• on Nokia SR OS routers that act as ASBRs the command enable-inter-as-vpn must be configured to permit advertisement of VPN‐labeled NLRI across an external BGP session.

Thus, only statement B, which makes LDP compulsory, is false.

A. MP-iBGP is indeed needed within every AS for VPN-IPv4 route dissemination, so the statement is correct.

C. ASBRs must run MP-eBGP to exchange labeled VPN routes across the AS boundary; the statement is correct.

D. Nokia SR OS requires enable-inter-as-vpn on ASBRs for option C; the statement is correct.

1. Nokia SR OS 22.x VPRN Guide, “Inter-AS Option C,” section 9.4.2, pp. 604-606 – notes that intra-AS transport may be LDP or RSVP-TE and describes MP-iBGP & MP-eBGP requirements.

2. Nokia SR OS 22.x BGP Guide, “enable-inter-as-vpn command,” section 8.2.1, p. 331 – states the command is mandatory on ASBRs to advertise VPN-IPv4/6 NLRI over eBGP.

3. Rosen & Rekhter, RFC 4364, sec. 10 (Option C) – specifies only “some MPLS tunneling technology” inside each AS, not necessarily LDP.

4. MIT 6.829 Course Notes, “BGP/MPLS IP VPNs” (Fall 2020), pp. 12-13 – summarizes that any MPLS transport (LDP or RSVP) suffices for option C, highlighting MP-eBGP between ASBRs.