Address and FEC Distribution

After an LDP LSR initializes the LDP session to the peer LSR and the session comes up, local IPv4 and IPv6 interface addresses are exchanged using the Address and Address Withdraw messages. Similarly, FECs are exchanged using Label Mapping messages.

By default, IPv6 address distribution is determined by whether the Dual-stack capability TLV, which is defined in RFC 7552, is present in the Hello message from the peer. This coupling is introduced because of interoperability issues found with existing third-party LDP IPv4 implementations.

The following is the detailed behavior:

The above behavior applies to LDP IPv4 and IPv6 addresses and FECs. The procedure is summarized in the flowchart diagrams in Figure 1 and Figure 2.

Figure 1. LDP IPv6 Address and FEC Distribution Procedure
Figure 2. LDP IPv6 Address and FEC Distribution Procedure