Had a problem today that doesn't make much sense to me.
Very simplified layout (hopefully not oversimplified...)
RTA -- RTB -- RTC
RTB gets a summary LSA for a network, call it 50.0.0.0, from RTA. This summary
LSA is visible with the command 'show ip ospf da su'.
There is also a static route for 50.0.0.0 on RTB, with admin distance 1. Not
surprisingly, this overrides the OSPF route in RTB's routing table. The static
route is NOT redistributed into OSPF.
RTB is adjacent with RTC. However the summary LSA for 50.0.0.0 does not get to
RTC (as shown by 'show ip ospf da su'), and RTC has no route to 50.0.0.0 (as
shown by 'show ip ro').
If the static route is taken off RTB, OSPF sends the summary LSA to RTC again,
and an OSPF route to 50.0.0.0 shows up in RTC's routing table.
I was under the impression that routing protocols are generally 'ships in the
night' in their operation (in that they each work out what they consider to be
the best route, and then the routing process chooses between routing protocols).
Why does adding a static route (not redistributed) affect what LSAs OSPF sends?
Shouldn't RTC get sent the summary LSA even though RTB has a better static route
- how does the OSPF process on RTB even know about the existence of the static
route??
Am I missing something really basic here?
The layout is in reality rather more complex - the RTA-RTB link is in the
backbone area, the RTB-RTC link is in a different area, and the summary route
originates from a third area. There are also redundant routers involved. If
you have any theories that involve complexities like this, I can give more
detail.
Ta,
JMcL
p.s. over in this part of the world, we have a far more popular race on the
first Tuesday in November, and it's got nothing to do with politics (probably
why it's more popular :-)
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