summarization

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Apr 4th, 2008
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I have a 3560 Multilayer switch that uplinks to the a router. The router's fa 0/0 interface is addressed 10.4.0.0/24. which leads to our WAN. Behind the 3560 on my LAN I have multiple VLANs, 10.4.1.0/24, 10.4.2.0/24, 10.4.3.0/24 etc. I'm running EIGRP on both the multilayer switch and router and redistributing EIGRP into RIPv2, RIPv2 is running on the edge routers that feed routes to the WAN. On the other end of the WAN those routers are getting my routes via the redistribution as /24 routes. How can I clean this up? If I change my IP address on my router's fa 0/0 interface to /16 can I then just advertise 10.4.0.0/16 to the WAN by using RIP and a network 10.4.0.0 255.255.0.0 command under RIP, and then turn off EIGRP on the multilayer switch and stop redistribution?

Will that work, or is there a better way to do it?


thank you,


Bill

Correct Answer by sundar.palaniappan about 9 years 2 months ago

Bill,


You don't have to tweak the subnet mask on the WAN facing interface as that would result in overlapping IP subnets usage in your network, though it may work it can potentially cause some problems. Use the 'ip summary-address' command under the WAN interface to advertise a summary-route as follows.


int s0/0

description wan connection

ip summary-address rip 10.4.0.0 255.255.0.0


http://www.cisco.com/en/US/docs/ios/12_0t/12_0t7/feature/guide/sumadr.html#wp19122


HTH


Sundar

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Correct Answer
sundar.palaniappan Fri, 04/04/2008 - 08:09
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Bill,


You don't have to tweak the subnet mask on the WAN facing interface as that would result in overlapping IP subnets usage in your network, though it may work it can potentially cause some problems. Use the 'ip summary-address' command under the WAN interface to advertise a summary-route as follows.


int s0/0

description wan connection

ip summary-address rip 10.4.0.0 255.255.0.0


http://www.cisco.com/en/US/docs/ios/12_0t/12_0t7/feature/guide/sumadr.html#wp19122


HTH


Sundar

WILLIAM STEGMAN Fri, 04/04/2008 - 08:23
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Sundar,


I was thinking about tweaking the mask of the lan interface rather than the wan interface.


right now I'm not advertising the 10.4.0.0 address at all under RIP. I'm redistributing the 10.4.0.0 routes learned via EIGRP into RIP. RIP is then used to carry those routes to remote sites across the WAN. So would I need to begin advertising network 10.4.0.0 255.255.0.0 under the RIP routing process before using the ip summary-address rip 10.4.0.0 255.255.0.0 command?

sundar.palaniappan Fri, 04/04/2008 - 08:36
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I don't have access to the lab at this time to test. However, I believe the routes should already be in the RIP database as result of the redistribution from EIGRP. Hence, just configuring the summmary address under the WAN interface should be sufficient for RIP to advertise the summary range. If you have any problems I shall be able to test it little later and post the results.


HTH


Sundar

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