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What is reason that ping can pass PE to reach destination but traceroute cannot?

[ Edited ]
‎05-22-2017 12:03 PM

Hi CRS router works as PE, and MX960 as CE. What is most possibly reason ping can pass PE and reach the destination, but traceroute cannot? The traceroute is launched from CE. But after three hops, it stops with continuous sign " * * * "

Thank you

3 REPLIES 3
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Re: What is reason that ping can pass PE to reach destination but traceroute cannot?

‎05-22-2017 08:15 PM

Hi, 

 

It could be that no-propagate-ttl or Cisco: no mpls ip propagate-ttl is configured on the MPLS network.

 

Cheers,

Ashvin

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Re: What is reason that ping can pass PE to reach destination but traceroute cannot?

‎05-22-2017 10:45 PM

Hi,

 

It might be because of no-propagate-ttl or no-decrement-ttl. The default operation of the JUNOS software with respect to time-to-live (TTL) is to copy the value from the IP packet to the MPLS header after decrementing it b y 1. The LSP routers decrement the value by one at each hop, and the value is rewritten to the IP header when the label is popped by the penultimate router. This default operation allows each hop in the LSP’s path to become visible to devices outside the MPLS domain.

 

Please refer to following links for more details:

 

https://www.juniper.net/documentation/en_US/junos/topics/usage-guidelines/mpls-disabling-normal-ttl-...

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/no-propag...

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/no-decrem...

https://www.juniper.net/documentation/en_US/junos/topics/example/vpns-vrf-ttl-decrement-disable.html

 


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Thanks

 

 

Hope this helps

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Routing

Re: What is reason that ping can pass PE to reach destination but traceroute cannot?

‎05-23-2017 03:14 AM

One of the reason is that traceroute uses udp packets while ping uses icmp . 

 

But you can try with traceroute monitor command (use icmp also).

 

no-propagete-ttl - also the reason