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traceroute vrf: One Hop appear two times

When I traceroute to an IP address belong to a vrf, I saw that it always has one hop with 2 times appearances.

Please help me describe the problem?

Here is the results:

HZZ-ZZZ-7609-01#traceroute vrf VPN-XXX-YYY 172.16.2.62

Type escape sequence to abort.

Tracing the route to 172.16.2.62

  1 192.168.0.125 [MPLS: Labels 37/942 Exp 0] 4 msec

    192.168.0.129 [MPLS: Labels 37/942 Exp 0] 0 msec

    192.168.0.125 [MPLS: Labels 37/942 Exp 0] 0 msec

  2 192.168.0.121 [MPLS: Labels 255/942 Exp 0] 12 msec 0 msec 0 msec

  3 172.16.29.2 [MPLS: Label 942 Exp 0] 4 msec 0 msec 0 msec

  4  *  *  *

  5 172.16.2.241 0 msec 4 msec 0 msec

  6 172.16.2.62 4 msec 0 msec 4 msec

Many Thanks in advance!

1 ACCEPTED SOLUTION

Accepted Solutions
Cisco Employee

traceroute vrf: One Hop appear two times

Hi there,

that is pretty normal if you have multiple path to reach the next hop and load balancing is performed.

As you see you get 3 responses for your first probe (the one with TTL=1), 2 from 192.168.0.125 and one from 192.168.0.129. That simply means that your router (the one you perform the traceroute from) has 2 next hops (2 paths) within your MPLS core to reach the egress PE and perform some load balancing.

The reason why you see this is because by default the traceroute tool in Cisco implementation sends 3 probes at a time for any given TTL value.

For instance if you change the value to 4 most likely you will see 2 response from one IP and 2 from the other, and so on.

Or if you change to 1 probe at a time you will see a single response from one of the 2 IP addresses.

regards,

Riccardo

3 REPLIES
Cisco Employee

traceroute vrf: One Hop appear two times

Hi there,

that is pretty normal if you have multiple path to reach the next hop and load balancing is performed.

As you see you get 3 responses for your first probe (the one with TTL=1), 2 from 192.168.0.125 and one from 192.168.0.129. That simply means that your router (the one you perform the traceroute from) has 2 next hops (2 paths) within your MPLS core to reach the egress PE and perform some load balancing.

The reason why you see this is because by default the traceroute tool in Cisco implementation sends 3 probes at a time for any given TTL value.

For instance if you change the value to 4 most likely you will see 2 response from one IP and 2 from the other, and so on.

Or if you change to 1 probe at a time you will see a single response from one of the 2 IP addresses.

regards,

Riccardo

New Member

traceroute vrf: One Hop appear two times

HI Riccardo,

Its right! I have two paths to reach to the next hop running mpls.

Many thanks for your quick reply!

Brgs,

Dat Ngo Quoc

Cisco Employee

traceroute vrf: One Hop appear two times

Hi Dat Ngo Quoc,

I am glad I helped.

Please rate the post and flag the question as answered if helpful.

Riccardo

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