Label Distribution Protocol
402
MPLS Guide
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5.2.5.2 OAM
LSPs are unidirectional tunnels. When an LSP ping is sent, the echo request is
transmitted via the tunnel and the echo response is transmitted as an IP packet to
the source. Similarly, for a p2mp-lsp-ping, on the root, the echo request is
transmitted via the mLDP point-to-multipoint tunnel to all leafs and the leafs use the
IP packet to respond to the root.
The echo request for mLDP is generated carrying a root Target FEC Stack TLV (see
Figure 28), which is used to identify the multicast point-to-multipoint LSP under test
at the leaf. The Target FEC Stack TLV must carry an mLDP point-to-multipoint FEC
Stack Sub-TLV from RFC 6388 or RFC 6512.
Figure 28 ECHO Request Target FEC Stack TLV
The same concept applies to inter-AS and non-segmented mLDP. The leafs in the
remote AS should be able to resolve the root via GRT routing. This is possible for
inter-AS Option C where the root is usually in the leaf RTM, which is a next-hop
ASBR.
OAM functionality for Option C is summarized in Table 40.
Table 40 OAM Functionality for Option C
OAM Command (for
mLDP)
Leaf and Root in Same AS Leaf and Root in Different
AS (Option C)
p2mp-lsp-ping ldp ✓✓
1041
Address Family
Opaque Length
Root LSR Address
Opaque Value...
Addr Length
01234567890123456789012345678901
1
23
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