Figure 5-9 Networking of PWE3 MH Tracert
CE1
UPE1
SPE1
P1
SPE2
UPE2
P2
CE2
The PWE3 tracert started on UPE1 can obtain 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 addition, you can
obtain information about PW label switching from the Downstream Mapping messages
sent by each device.
On SPE1, start PWE3 tracert to UPE1 or to SPE2 and UPE2. The PWE3 tracert to UPE1
is the same as the PWE3 SH tracert. The PWE3 tracert to SPE3 and UPE2 is PWE3
MH tracert.
PWE3 tracert started on other PEs is the same as the preceding PWE3 tracert, and is not
mentioned here.
The relations between MPLS ping and PWE3 ping, and between MPLS tracert and PWE3 tracert
are as follows:
l MPLS Ping
MPLS ping is the similar to IP ping. The source node sends an MPLS echo request packet.
The packet is forwarded by nodes along the LSP. When the packet reaches the egress in
the MPLS area, the egress replies an MPLS echo reply packet. If the source node receives
the MPLS echo reply packet from the destination node, the source node considers that the
LSP can be used to forward data; otherwise, the source node regards that the LSP cannot
be used to forward data.
l MPLS Tracert
The source node of MPLS tracert continuously sends MPLS echo request packets with TTL
values from one to a certain value. After the TTL of each node on the LSP times out, each
node replies an MPLS echo reply packet. The ingress thus can collect information about
each node on the LSP, and then locate the faulty node. At the same time, MPLS tracert can
be used to collect important information about each node on the entire LSP, such as assigned
labels.
l PWE3 Ping
The principle of PWE3 ping is similar to the principles of MPLS ping and IP ping. The
difference lies in that PWE3 ping uses a PW to forward MPLS echo request packets to
5 PWE3 Configuration
Quidway S9300 Terabit Routing Switch
Configuration Guide - VPN
5-10 Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
Issue 03 (2009-08-20)
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