Multi-segment PW
A multi-segment PW includes multiple concatenated static or LDP PWs. Creating two PWs for a cross-connect on a PE can concatenate the two PWs. Upon receiving a packet from one PW, the PE removes the tunnel ID and PW label of the packet, adds the PW label of the other PW, and forwards the packet over the public tunnel. Only static and LDP PWs can form a multi-segment PW.
As shown in Figure 69, you can create a multi-segment PW between PE 1 and PE 4 by concatenating PW 1 and PW 2 on PE 2, and PW 2 and PW 3 on PE 3.
Figure 69: Multi-segment PW
Multi-segment PWs include intra-domain multi-segment PWs and inter-domain multi-segment PWs.
Intra-domain multi-segment PW
An intra-domain multi-segment PW has concatenated PWs within an AS. You can create an intra-domain multi-segment PW between two PEs that have no public tunnel to each other.
As shown in Figure 70, there is no public tunnel between PE 1 and PE 4 but there is a pubic tunnel between PE 1 and PE 2 and a public tunnel between PE 2 and PE 4. By creating a PW between PE 1 and PE 2 (PW 1) and a PW between PE 2 and PE 4 (PW 2) and then concatenating the two PWs on PE 2, you can create an intra-domain multi-segment PW between PE 1 and PE 4.
Intra-domain multi-segment PWs can fully unitize existing public tunnels to reduce end-to-end public tunnels.
Figure 70: Intra-domain multi-segment PW
Inter-domain multi-segment PW
An inter-domain multi-segment PW has concatenated PWs in different ASs, and is a method for inter-AS option B networking.
As shown in Figure 71, you can create an inter-domain multi-segment PW between PE 1 and PE 2 in different ASs by concatenating PW 1 and PW 2 on ASBR 1 and concatenating PW 2 and PW 3 on ASBR 2.
Figure 71: Inter-domain multi-segment PW
