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

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-decrementing.html

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/no-propagate-ttl-edit-protocols-mpls.html

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/no-decrement-ttl-edit-protocols-mpls.html

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

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Thanks