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
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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
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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
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What are the reason to disable MPLS TTL propagation?
-Security Exposure for SP
-Customers find IP address of LSR (confusing for customer)
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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
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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
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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)
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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
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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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