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вторник, 18 октября 2011 г.

OSPF E1 vs N1 vs E2 vs N2

1. N1 & E1 are preferred over N2 & E2 for the same route
2. When N1 & E1 have the same route to the destination, The one that have lower cost / Metric will win and get into the route table
3. If both N1 & E1 have the same cost, P-bit in N1 will be used to break the tide.
4. If P-bit is 0 (Then it would become E1) then we will have 2 E1 routes install into the routing table. (otherwise if maximum-path = 1, LSA with Higher Router-ID will get installed)

See rfc 3101 for details.

Update1. Cisco IOS OSPF realization is significantly differs from RFC:
http://blog.ioshints.info/2008/01/e1-and-e2-routes-in-ospf.html This article is outdated.

Update2.  Enable 'capability rfc1587' to fall back to the "E2 is preferred over N2" route selection algorithm.

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