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How to check each hop in MPLS network

Publication Date:  2014-03-29 Views:  164 Downloads:  0
Issue Description
By default,NE router hides all the hops on the MPLS network, as if the ingress node is directly connected to the egress node. 
For example:

When tracert from client1 to client2, the intermediate hop 172.1.1.2 is hided.

PC>tracert 10.2.1.100

traceroute to 10.2.1.100, 8 hops max
(ICMP), press Ctrl+C to stop
1  10.1.1.2   16 ms  16 ms  <1 ms
2  10.2.1.2   31 ms  32 ms  31 ms
3  10.2.1.100   31 ms  16 ms  31 ms
Alarm Information
None
Handling Process
1. Enable MPLS to process the TTL in uniform mode.
<HUAWEI> system-view
[HUAWEI] ip vpn-instance vpna
[HUAWEI-vpn-instance-vpna] ipv4-family
[HUAWEI-vpn-instance-vpna-af-ipv4] ttl-mode uniform
2. Reset LDP session
<HUAWEI> reset mpls ldp
3. Test again on client1, the intermediate hops is shown as below:
PC>tracert 10.2.1.100

traceroute to 10.2.1.100, 8 hops max
(ICMP), press Ctrl+C to stop
1  10.1.1.2   <1 ms  16 ms  16 ms
2  172.1.1.2   31 ms  31 ms  31 ms
3  10.2.1.2   63 ms  31 ms  47 ms
4  10.2.1.100   31 ms  31 ms  31 ms

PC>
Root Cause
When the uniform mode is configured, each time packets pass by a hop on an MPLS network, the value of the IP TTL decreases by 1. The output of traceroute shows actual hops by which the packets pass.
When the pipe mode is configured, the packets pass by a hop on an MPLS network, the value of the IP TTL decreases by 1 only on the ingress and the egress. The whole MPLS domain functions as one hop. The output of traceroute, however, does not show all hops by which the packets actually pass.
By default, MPLS processes the TTL in pipe mode on NE router.
Suggestions
When you needs the detailed hops in MPLS network, please configure the ttl mode to uniform.

END