summarization

Unanswered Question
mohammedmahmoud Mon, 05/07/2007 - 01:33

Hi,

To configure a summary aggregate address , use the "ip summary-address eigrp as-number network-address subnet-mask" command in interface configuration mode

interface ethernet 0

ip summary-address eigrp 109 192.168.0.0 255.255.0.0 --> Note that the subnet mask here is not written as wildcard

The router will advertise the summarized route only to its neighbor through this interface, while adding the summarized route to its null interface in its routing table and keeping the more specific route to be used when the neighbor routed packets arrived in order to be used.

NOTE: EIGRP summary routes are given an administrative distance value of 5 by default, can be changed in the summary command.

NOTE: The more specific route needs to be in the routing table for the summary route to be originated.

HTH, please rate all helpful posts,

Mohammed Mahmoud.

mohammedmahmoud Mon, 05/07/2007 - 01:56

hi,

You should do the summarization from the DS towards the Core.

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

HI mohammedmahmoud!

Kindly check attached file;so what this config does;sumarization from the CORE Toward the DSs

CORE!

Interface Portchannel200

descr connection to DS1

ip address 192.168.200.1 255.255.255.252

ip summary-address eigrp 1 10.250.0.0

!

Interface Portchannel100

descr connection to DS2

ip address 192.168.200.37 255.255.255.252

ip summary-address eigrp 1 10.250.0.0

!

Interface Portchannel1

descr connection to DS3

ip address 192.168.200.29 255.255.255.252

ip summary-address eigrp 1 10.200.0.0

!

***************************

CORE:Network:10.100.0.0 *

DS1: Network:10.200.0.0 *

DS2: Network:10.200.0.0 *

DS3: Network:10.250.0.0 *

***************************

this config work perfect but i didn't undesstand why the Summary from the CORE Towards the DSs.plz explain

Attachment: 
mohammedmahmoud Mon, 05/07/2007 - 05:34

Hi,

For the best practice you should do the summarization from the DS towards the Core, may be in your case there was a special issue to be considered, may be due to the direct link between DS1 and DS2.

HTH,

Mohammed Mahmoud.

mahmoodmkl Mon, 05/07/2007 - 08:05

HI Ali

the config is missing subnet mask in the

ip summary-address eigrp 1 10.200.0.0 (subnet mask)

Thanks

Mahmood

mohammedmahmoud Mon, 05/07/2007 - 10:16

Hi Ali,

When doing EIGRP summarization using this command, the router adds a summary route to null in its routing table automatically and advertise this route, but when the packet to be routed arrives at the router it is routed via the more specific route rather than this null route. (note that the route won't be summarized in the first place unless the more specific route was there).

HTH, please do rate helpful replies,

Mohammed Mahmoud.

hoogen_82 Mon, 05/07/2007 - 10:41

Well if you can look at in a logical way. Your core router would have more routes, routes from external routers, you probably could have a ton of information there, but you would for your distribution switches which may have lesser processing power to have lesser overheads when trying to reach external routes. For reaching any of your external routes or destination a simple default route (summarizes everything) would be just enough on your distribution. Your core could do more specific routing once the packet is recieved there.

-Hoogen

Do rate if this helps :)

mohammedmahmoud Mon, 05/07/2007 - 11:48

Hi,

As a best practice we do summarize from the distribution layer into the core via summary-address, summarization within the core is unnecessary. Because each distribution layer router is sending only summary information to the core, it is probably unnecessary to further summarize between core routers. However sometimes it is useful to summarize between core routers, or between the core and the distribution to minimize routing tables more, especially when the distribution routers are not that powerful.

HTH,

Mohammed Mahmoud.

Amit Singh Tue, 05/08/2007 - 09:53

Ali,

You have to just configure the summarization on the DS4 link i.e 10.150.0.0 to send it core. Once core has got it or the other summary routes they all will be automatically advertised by core switch to the other switches.You dont have to manually configure the core switch interfaces to advertise all the specific routes.

If you want to control or filter the summary routes advertisement from core to other switches you have to use distribute list.

-amit singh

mohammedmahmoud Tue, 05/08/2007 - 10:08

Hi Ali,

I am glad that your are being an EIGRP expert now :), you'll just need "ip summary-address eigrp" command on the interface of CORE towards the new DS, use as many of this command as the networks you need to summarize (as long as the more specific routes are in the routing table).

HTH, please do rate all helpful replies,

Mohammed Mahmoud.

mohammedmahmoud Tue, 05/08/2007 - 10:31

Hi,

For the summary route to be sent, the more specific route(s) must be in the routing table (at least one of the more specific routes to be summarized must be in the routing table).

You can use as many "ip summary-address eigrp" command as you need under the interface, example:

ip summary-address eigrp 101 192.168.0.0 255.255.0.0

ip summary-address eigrp 101 10.10.0.0 255.255.0.0

and so on.

HTH, please do rate all helpful posts,

Mohammed Mahmoud.

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