You want to ensure that your all-Junos MPLS core network does not decrease the TTL when
using ping and traceroute from IP endpoints. Which two configuration parameters satisfy this
requirement? (Choose two.)
A.
no-decrement-ttl, configured on all routers in the path
B.
no-decrement-ttl, configured on the ingress router only
C.
no-propagate-ttl, configured on all routers in the path
D.
no-propagate-ttl, configured on the ingress router only
Explanation:
Am thinking the answers should be B and D (not C)
http://www.juniper.net/documentation/en_US/junos13.2/topics/usage-guidelines/mpls-disabling-normal-ttl-decrementing.html
There are two ways to disable TTL decrementing:
• On the ingress of the LSP, if you include the “no-decrement-ttl” statement, the ingress router negotiates with all downstream routers using a proprietary RSVP object, to ensure all routers are in agreement. If negotiation succeeds, the whole LSP behaves as one hop to transit IP traffic.
•
• On the ingress router, you can include the “no-propagate-ttl” statement. The no-propagate-ttl statement applies to all LSPs, regardless of whether they are RSVP-signaled or LDP-signaled. Once set, all future LSPs traversing through this router behave as a single hop to IP packets. LSPs established before you configure this statement are not affected.
•
•
• NOTE: The operation of the no-propagate-ttl statement is interoperable with other vendors’ equipment. However, you must ensure that all routers are configured identically.
The last note means you configure no-propagate-ttl on all routers only when working with routers from multiple vendors. In this question we only have junos routers. hence can configure no-propagate-ttl only on the ingress router
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I think answer is B & D.
Once set, all future LSPs traversing through “THIS ROUTER” behave as a single hop to IP packets.
The operation of the no-propagate-ttl statement is interoperable with other vendors’ equipment. However, you must ensure that all routers are configured identically.
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Sorry, I think answer is B & C.
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B & C correct. answer
There are two ways to disable TTL decrementing:
•On the ingress of the LSP, if you include the no-decrement-ttl statement, the ingress router negotiates with all downstream routers using a proprietary RSVP object, to ensure all routers are in agreement. If negotiation succeeds, the whole LSP behaves as one hop to transit IP traffic.
no-decrement-ttl;
For a list of hierarchy levels at which you can include this statement, see the statement summary section for this statement.
Note: The RSVP object is proprietary to the Junos OS and might not work with other software. This potential incompatibility applies only to RSVP-signaled LSPs. When you include the no-decrement-ttl statement, TTL hiding can be enforced on a per-LSP basis.
•On the ingress router, you can include the no-propagate-ttl statement. The no-propagate-ttl statement applies to all LSPs, regardless of whether they are RSVP-signaled or LDP-signaled. Once set, all future LSPs traversing through this router behave as a single hop to IP packets. LSPs established before you configure this statement are not affected.
no-propagate-ttl;
You can include this statement at the following hierarchy levels:
•[edit protocols mpls]
•[edit logical-systems logical-system-name protocols mpls]
The operation of the no-propagate-ttl statement is interoperable with other vendors’ equipment. However, you must ensure that all routers are configured identically.
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