JNCIS-SP Exam - Question 47

Question

You are troubleshooting two OSPF routers that have an adjacency that remains in the ExStart state. What would cause this problem?

Examice · Accepted Answer

When troubleshooting OSPF routers that have an adjacency remaining in the ExStart state, the most likely cause is mismatched MTU (Maximum Transmission Unit) settings on the OSPF interfaces. If the MTU settings do not match, the router with the higher MTU may send packets that are larger than what the neighboring router can handle, causing the packets to be ignored and preventing the formation of a proper adjacency.

networkwalker · Answer

https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13684-12.html#anc13

Neighbors Stuck in Exstart/Exchange State
The problem occurs most frequently when you attempt to run OSPF between a Cisco router and another vendor router. The problem occurs when the maximum transmission unit (MTU) settings for neighboring router interfaces do not match. If the router with the higher MTU sends a packet larger that the MTU set on the neighboring router, the neighbor router ignores the packet. When this problem occurs, the output of the show ip ospf neighbor command displays output similar to what is shown in this figure.

Sailor · Answer

https://community.juniper.net/communities/community-home/digestviewer/viewthread?MID=71714

Two things generally cause this. Mismatched MTU and firewall filter on loopback interface.

c946f3e · Answer

The problem occurs when the maximum transmission unit (MTU) settings for neighboring router interfaces do not match

JNCIS-SP Exam - Question 47

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