2 T1-CSU/DSU one router two carriers.. how to switch over

[aseamans]

Hello all..

We are in the process of switch T1 carriers and want to use a single 2621 for the switch over. We have two sets of Ip addresses (one old and the other new.) How do i go about doing the switch over if I want to do it gradually?

I assume that with 2 WICs I can do a static route to each one.(each ip range is on a seperateFE interface) For example if I have the ip form one carrier (2.2.2.0) and the ips from the new carrier (3.3.3.0) the current default route is:

ip route 0.0.0.0 0.0.0.0 s0/0

can I change those to be:

ip route 2.2.2.0 0.0.0.255 s0/0

ip route 3.3.3.0 0.0.0.255 s0/1

would that work correctly?

thanks for any help you can give on this.

[trackme]

Hi,

Are you going to retain the old subnet is 2.2.2.0 and want only to use 3.3.3.0.

If that is the case you can do like this

ip route 0.0.0.0 0.0.0.0 s0/0

ip route 0.0.0.0 0.0.0.0 s0/1 metric 10

In this way the all the traffic will see only one gateway at any given point of time .So if you turn off the s0/0 interface then all the traffic will go through the s0/1 which is your new ISP without any downtime.

Note : this works fine only for outgoing traffic from your network,for incoming traffic this setup will not work in the sense you may have some packet loss

Hope this helps,

regards

Anantha

[aseamans]

basically we are switching to a new ISP... so the old subnet will go away eventually but not until after the new subnet is in place and switched over... we would do a massive switch but our email and web server would go down for a few days if we did... so we thought it best to multihome the web/email server until after the DNS changes took place then switch everything else over...