Hi,
is this only an exercise or you really need to do this? If the latter, then
I would be curious to know why this would be useful. I feel a slight
contradiction in that you can't control whether a /24 or two /25 routes
reach you yet you seem to know what is in one half versus the other half of
the /24 network and want to make some routing decision based on this
knowledge.
Anyway, to answer your question, the obvious solution is to point the two
/25 static routes towards where you learn the /24 route from, not to Null0.
If you have only one IGP peer, then simply point them towards it.
If you have multiple IGP peers, then it gets a bit ugly. You could create a
loopback address on the router where x.x.x.x/24 (or the two /25 networks)
is directly connected, advertise the loopback(s) through the same IGP
protocol which carries the x.x.x.x/24 route, and point the two /25 static
routes to the loopback address(es). Or (assuming the IGP is OSPF and
x.x.x.x/24 is in another area) you could use the loopback address of some
backbone routers (possibly creating multiple pairs of static routes, each
with different admin distance pointing to a different backbone router).
The main thing to note in either case is that if you ever, for any reason,
happen to advertise back these /25 routes towards where you learn the /24
route from, or if the router you pointed your static route to ever thinks
that your router is the best way to get to x.x.x.x/24, then you just
created a routing loop.
Btw, why is it that the IGP will only send the /24 and not the two /25s?
Getting the two /25s instead of the one /24 might be as easy as configuring
a secondary IP address on that interface or (selectively) disabling
summarization. This of course depends on your situation, so just something
to think about...
Thanks,
Zsombor
At 11:39 PM 6/21/2003 +, p b wrote:
Suppose I have a router which has a subnet x.x.x.0/24 defined
on some interface. Over one iBGP session I'd like to
advertise the x.x.x.0/24 subnet. Over another iBGP session,
I'd like to advertise x.x.x.0/25 and x.x.x.128/25. When
I config three network statements for these subnets in BGP,
only the /24 seems to be sent to the one iBGP peer.
If I define a static null route for each subnet (x.x.x.0/24,
x.x.x.0/25, and x.x.x.128/25), all three routes are advetised.
Is there a way to get the /24 and two /25s sent without
the null route? In actuallity, the /24 will be learned
via some IGP, so can't use the nulls and the IGP will
only send the /24 and not the two /25s.
Thanks
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7i=71210t=71073
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