Huawei quidway s7700 Configuration Manual page 565

Quidway S7700 Smart Routing Switch
Configuration Guide - VPN
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CW
The PWE3 supports CW.
The CW is a four-octet header in some encapsulations, and is used for sending packet information
in MPLS PSN.
On the PWE3 control plane, there is a bit symbolizing whether the CW presents on the PW or
not.
On the PWE3 data plane, if the CW is supported, a four-octet control word is added in the header
of the packet to indicate the sequence of the packet.
Negotiation will be carried out successfully only when both endpoints of the PW support CW,
or do not support CW at the control layer. The CW is optional. For static PW, CW requirements
are configured manually.
Issue 01 (2011-07-15)
addition, the PW label switching from the downstream mapping information sent
by each device can be seen.
– 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 SPE2 and UPE2 is
PWE3 MH tracert.
– PWE3 tracert started on other PEs is the same as the preceding ones, and is not
described here.
The relations between MPLS ping and PWE3 ping and between MPLS tracert and PWE3
tracert are as follows:
MPLS ping
MPLS ping is 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 with an MPLS echo reply packet. If the source node receives
the MPLS echo reply packet from the destination node, it considers that the LSP can be
used to forward data; otherwise, the source node considers that the LSP cannot be used to
forward data.
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 expires, 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.
PWE3 ping
The principle of PWE3 ping is similar to that of MPLS ping and IP ping. The difference
lies in that PWE3 ping uses a PW to forward MPLS echo request packets to judge whether
the PW can be used to forward packets. When MPLS ping succeeds, PWE3 ping may fail.
PWE3 Tracert
The principle of PWE3 tracert is similar to that of MPLS tracert and IP tracert. The
difference lies in that PWE3 tracert uses a PW to forward MPLS echo request packets to
collect information about nodes on the PW. When MPLS tracert succeeds, PWE3 tracert
may fail.
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6 PWE3 Configuration
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