summarising addressess

[carl_townshend]

Hi all, what protocols can we summarize addresses with, ie reigrp etc, also if I summarize on an interface, why not just summarise when including the network statement when u set the routing protocol up ?

[m-haddad]

Hello,

You can do network aggregation or summarization on any routing protocol. However, please note that the network statement under the protocol indicates which interface will participate in the routing protocol. For example, when you use the command network 10.20.30.4 0.0.0.0 area 0 under the ospf you'er specifying that this interface will participate in the OSPF neighbor relationship however, the interface subnet mask will be advertised as /24 if it was /24.

If you set the network statement to network 10.20.30.0 0.0.0.255 area 0 this does not mean you will summarize the advetisement! However, this means all interfaces under the address 10.20.30.0/24 will participate in OSPF and will be advertised in OSPF. However, they will be advertised with their native subnet mask.

To summarize advertisements you can turn auto-summary ON under the routing process and it will summarize the routes or you can use the summary address command to advertise them in aggregates aswell.

Therefore, do not mix between the network statement and advertisement.

Let me know if this helps and if you need further explanantion,

Regards,

[carl_townshend]

can u give me an example with eigrp ?

[m-haddad]

Here you go Carl,

Scenario:

R1

LAN1 IP: 10.20.30.254/24

WAN IP: 62.84.65.254/24

LAN2 IP: 10.20.40.254/24

If you go under the eigrp and type:

network 10.20.30.254 0.0.0.0

The advertised subnet will be 10.20.30.0/24 eventhough in your EIGRP configuration you set only the IP 10.20.30.254. This means the network command is used to specify which interface will run the protocol and establish neighbor relationship.

If you put:

network 10.20.0.0 0.0.255.255

This means both LAN1 and LAN2 will try to run EIGRP and establish neighbor relationships. However, the advertised subnets will be:

10.20.30.0/24

10.20.40.0/24

Of course the above is correct if you have auto-summary under the eigrp turned off.

I hope this clarified the issue,

Let me know if you require anything else,

Regards,