From: Adam Asay (aasay@cerberian.com)
Date: Tue May 20 2003 - 14:30:55 GMT-3
Oliver,
Whenever a router is performing route summarization the routing table
will show the summarized route, and the more specific routes in the
routing table.
The specific routes will be shown in the routing table because they are
directly connected, and not being learned via the routing protocol you
are using.
You will also see the summarized route with a next hop of null 0. This
is OK. Since you are summarizing the routes your routing table should
always contain the more specific routes, and will make the routing
decision based on the specific routes. Also if there are other networks
that your router is not aware it gives the router a chance to drop any
packets destined for these addresses. For example in your topology if
router 4 tried to send a packet to 172.16.5.1, it would think this route
is available via R1. When the packet reaches R1 it will go ahead and
drop it because it does not contain a route to this network.
I hope this helps.
Adam Asay
Sr Systems Engineer
www.cerberian.com
On Tue, 2003-05-20 at 09:55, Oliver Ziltener wrote:
> I have this setup:
>
>
> R1 ----- R2 ----- R5/R6/R4
>
>
> R1 is in area 0001
> R2,R4,R5,R6 in area 0100
> Alle router are is-type L1/L2
>
> The links between R2 and R5/R6/R7 are FR p2p with a /30 mask.
> On R1, I have 3 loopbacks.
>
> The summarisation of the loopbacks into Area 0100 works fine-i receive only
> the summary!
> The summarisation of the p2p links into Area 0001 works as expected, I got
> the summary and the 3 more specific ones.
>
> Any idea why i get the more specific and the summary on R1??
>
> And second, I discoverd also, when i do "clear ip route " the Summary null0
> router will till the next reload not appear in the routing table...?Bug???
>
> thanks
> Oliver
>
> R1#
> router isis
> summary-address 172.16.0.0 255.255.252.0
> passive-interface Loopback10
> passive-interface Loopback11
> passive-interface Loopback12
> passive-interface Loopback13
> net 49.0001.1111.1111.1111.00
> log-adjacency-changes
>
> R1#
> 172.16.0.0/16 is variably subnetted, 5 subnets, 2 masks
> i su 172.16.0.0/22 [115/0] via 0.0.0.0, Null0
> C 172.16.0.0/24 is directly connected, Loopback10
> C 172.16.1.0/24 is directly connected, Loopback11
> C 172.16.2.0/24 is directly connected, Loopback12
> 192.168.100.0/24 is variably subnetted, 4 subnets, 2 masks
> i L2 192.168.100.8/30 [115/30] via 192.168.200.2, Ethernet0/1 <<more
> specific
> i L2 192.168.100.4/30 [115/30] via 192.168.200.2, Ethernet0/1 <<more
> specific
> i L2 192.168.100.0/30 [115/30] via 192.168.200.2, Ethernet0/1 <<more
> specific
> i L2 192.168.100.0/28 [115/20] via 192.168.200.2, Ethernet0/1
> <<<<<Summary!
> R1#
>
>
> R2#
> router isis
> summary-address 192.168.100.0 255.255.255.240
> net 49.0100.2222.2222.2222.00
> log-adjacency-changes
>
> R2#
> 172.16.0.0/22 is subnetted, 1 subnets
> i L2 172.16.0.0 [115/10] via 192.168.200.1, Ethernet0/0<<<only the summary
> C 192.168.100.8/30 is directly connected, Serial0/0.6
> C 192.168.100.4/30 is directly connected, Serial0/0.5
> i su 192.168.100.0/28 [115/10] via 0.0.0.0, Null0
> C 192.168.100.0/30 is directly connected, Serial0/0.4
> R2#
This archive was generated by hypermail 2.1.4 : Mon Jun 02 2003 - 15:13:45 GMT-3