Huawei quidway s7700 Configuration Manual page 564

Quidway S7700 Smart Routing Switch
Configuration Guide - VPN
Figure 6-10 Networking diagram of PWE3 MH tracert
UPE1
Issue 01 (2011-07-15)
– The source PE of the PWE3 tracert continues to send MPLS echo request packets
with the Time-to-Live (TTL) of the outer label from one to a certain value and the
TTL of the inner label as one. Each Label Switching Router (LSR) does not forward
the received packet with the TTL of the outer label as one. Based on the contents of
the packet, each LSR checks the correctness of specific services and labels, and then
sends an MPLS echo reply packet to the source PE. In this way, the source PE can
collect information about each LSR that a PW passes through and information about
the egress PE. At present, the MPLS echo reply packet is an IP packet that does not
carry any label.
– The LSP between PE1 and PE4 is used as an example to explain the mechanism
used by PWE3 tracert to collect information about nodes.
– By starting PWE3 tracert, PE1 can collect information about nodes that the LSP
from PE1 to PE4 passes through. By comparing paths obtained by the PWE3 tracert
and PW paths generated by the protocol, you can judge whether or not there is an
error.
– If the PWE3 tracert obtains only information about PE4 (TTL=2) instead of
information about P (TTL=1), it indicates that P does not support MPLS ping.
– If the PWE3 tracert obtains only information about P (TTL=1) instead of information
about PE4 (TTL=2), it indicates that PE4 or the link between P and PE4 is faulty.
– If the PWE3 tracert obtains information about PE1, PE2, and PE4, it indicates that
P may be faulty. A new path is generated by the protocol.
– PWE3 MH tracert
– As shown in Figure
of PW segments are different. The LSP is UPE1-P1-SPE1-SPE2-P2-UPE2.
–
P1
SPE1
CE1
– The PWE3 tracert started on UPE1 can obtain a correct response only from P1 and
SPE1. SPE2 and UPE2 find that the "Remote PE Address" and "VC ID" are not
consistent. This indicates that the PWE3 tracert passes through an MH PW. In
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6-10, an MH PW is set up between CE1 and CE2, and the IDs
SPE2
6 PWE3 Configuration
CE2
UPE2
P2
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