9 good questions and answers: "The MPLS TTL Field and MPLS TTL Propagation"

What are the two important feature of the (MPLS) TTL Field?
-Identify looping packets
-Used for traceroute
What does the Ingress E-LSR do with the TTL field when it recieves an IP packet? 3
-decremens the IP TTL field
-pushes a label into unlabeled packet
-copies the packet IP TTL field into the new MPLS header's TTL field
What is the behavior of the traceroute command with MPLS?
Traceroute command would recieve ICMP Time Exceeded messages form each of the  routers including LSR's
What are the reason to disable MPLS TTL propagation?
-Security Exposure for SP
-Customers find IP address of LSR (confusing for customer)
What is the behavior when MPLS TTL propagation is disabeld? 2
-E-LSR routers sets MPLS header to 255
-Egress E-LSR leaves Original header's TTL field unchanged
How does the MPLS network appear for the customer when MPLS TTL propagation is disabeld?
Entire MPLS network appears to be single router hoop from TTL perpective
What are the abilities to disable MPLS TTL propagation?
-TTL propagation for packect forwarded by customer (forwarding traffic)
-TTL propagation for packets created by SP's router (locally originated traffic)
What is the command to disable MPLS TTL propagation and where should it be configured?
no mpls ip propagate-ttl

All routers in the MPLS domain should TTL disable for consistent output of the TTL propagation
What is the command for mpls ping? Why would you like to use it?
ping mpls ipv4

"Normal" does not give all the information to check if there's a problem
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