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[ScreenOS] Why does the OSPF neighborship with Cisco stop working after the hello interval was changed on both devices?

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Summary:

This article describes the issue of the OSPF neighborship not coming up, after the Hello timer was changed from the default value of 10 seconds to 15 seconds on both peers.

Symptoms:

The OSPF neighborship is not coming up, after the Hello timer was changed from the default value of 10 seconds to 15 seconds on both peers.

Cause:

On NetScreen, the Hello interval and the Dead interval can be individually configured; however, on Cisco, as soon as the Hello interval is set, the Dead interval changes to a value that is 4 times the value of the hello interval.

So, when the Hello interval is changed from 10 to 15 seconds, the Dead timer remained at 40 seconds on the NetScreen firewall. However, the same timer was changed to 60 seconds on Cisco. The OSPF neighborship did not come up due to this timer mismatch.

Solution:

To resolve this issue, manually change the Dead interval on the NetScreen firewall as well to a value that is 4 times the Hello interval, so that this matches the timers on the peers.

Modification History:
2019-09-27: Made minor clarification in solution field.
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