09-22-2006 10:19 PM - edited 03-03-2019 02:05 PM
Hi,
I have a question about RIP routing:
I have 2 routers (A and B) connected to each other via an ATM wan link.
Each router has several routes in his routingtable.
For example: router A has a route to 10.0.0.0/16, 10.0.1.0/24, 10.0.2.0/24,...
Router A has to advertise to router B the 10.0.0.0/16 and not the /24's.
I've created an access-list 1:
access-list 1 permit 10.0.0.0 0.0.255.255.
And put it in the router rip:
distribute-list 1 out atm1/0
Unfortunately the /16 is advertised, but so are the /24's.
When I change the ACL to:
access-list 1 deny 10.0.1.0 0.0.0.255
access-list 1 deny 10.0.2.0 0.0.0.255
access-list 1 permit 10.0.0.0 0.0.255.255
No routes are being advertised at all by rip and counters on the first deny are rising.
Has anybody got an idea ?
Thanks,
tom
09-23-2006 01:30 AM
Hi Tom,
RIP automatically summarizes to classful network boundaries.
"Cisco routers can summarize routes in two ways:
- Automatically, by summarizing subprefixes to the classful network boundary when crossing classful network boundaries (autosummary)
- As specifically configured, advertising a summarized local IP address pool on the specified interface, (on a network access server) so that the address pool can be provided to dialup clients
Autosummary addressing always summarizes to the classful address boundary, while the ip summary-address command summarizes addresses on a specified interface. If autosummary addressing is enabled, autosummarization is the default behavior for interfaces on the router not associated with dial-in clients (the "backbone"), with or without the ip summary-address rip interface subcommand present.
For example, if a local IP address pool of 10.1.1.1 to 10.1.1.254 is configured on the network access server, you could configure the ip summary-address rip 10.1.1.0 255.255.255.0 command on the network access server port that provides addresses to dialup clients to cause the router to advertise 10.1.1.0/24 routes to dialup clients. Because a summary route is advertised, advertisement of the /32 host routes (installed when the dialup client connects) is suppressed so that the router does not advertise these routes to the network access server interface.
- Autosummary will override the configured summary-address feature on a given interface except when both of the following conditions are true:
- The configured interface summary-address and the IP address of the configured interface share the same major network (the classful, nonsubnetted portion of the IP address).
- Split horizon is not enabled on the interface.
..."
From 12.0(6)T you can use the 'ip summary-address rip' on ATM interface (and if your RIP cloud is only 2 routers, use 'no ip split-horizon' whitout any problem).
http://www.cisco.com/en/US/products/sw/iosswrel/ps1830/products_feature_guide09186a0080087ad1.html
Try something like that:
interface ATM x
ip address 10.0.0.1 255.255.0.0
ip summary-address rip 10.0.0.0 255.255.0.0
no ip split-horizon
HTH
Andrea
09-25-2006 04:07 AM
Hi Andrea,
It works ! great !
Only problem, I have to use an 10.0.X.X ip address on the wan (point to point) link otherwise it doesn't work. For my other lines i use 192.168.X.X addresses.
Thanks anyway !
(you've been a great help)
tom
09-23-2006 06:36 AM
Hey Tom,
Could you show us the output of "show ip route" in both routers before and after the ACL?
I've implemented the same setup in a lab and it worked with no problem using the last ACL.
BEFORE ACL:
R2>show ip route
R 10.0.2.0/24 [120/1] via 10.0.4.1, 00:00:01, FastEthernet0/0
R 10.0.3.0/24 [120/1] via 10.0.4.1, 00:00:01, FastEthernet0/0
R 10.0.0.0/16 [120/2] via 10.0.4.1, 00:00:01, FastEthernet0/0
C 10.0.4.0/30 is directly connected, FastEthernet0/0
C 10.0.5.0/24 is directly connected, FastEthernet1/0
AFTER dist-list with ACL 1
R2>SHOW IP ROUTE
R 10.0.0.0/16 [120/2] via 10.0.4.1, 00:00:01, FastEthernet0/0
C 10.0.4.0/30 is directly connected, FastEthernet0/0
C 10.0.5.0/24 is directly connected, FastEthernet1/0
acl:
access-list 1 deny 10.0.2.0 0.0.0.255
access-list 1 deny 10.0.3.0 0.0.0.255
access-list 1 permit 10.0.0.0 0.0.255.255
router rip
distribute-list 1 out fa0/0
Let us know,
Vlad
09-25-2006 04:06 AM
Hi Vlad,
Thanks for your reply.
The ACL works partially for me, the problem is:
Router A has a route to 10.0.0.0/24 (connected) and a route to 10.0.0.0/16 (static)
The static route should be advertised but not the 10.0.0.0/24.
Any idea ?
Thanks,
tom
09-30-2006 05:00 AM
hello Tom, sorry for the delay.
Again, I used the same ACL and dist-list and it worked as required. /16 was advertised but not the /24.
Maybe there's something else with the configs.
Give us more details, we might find the problem.
Vlad
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