A second default gateway

[steve]

This is a sort of generalised question. Someone has asked, and am actually scratching my head thinking that he has the wrong end of the stick entirely and I want to put him straight.

The sceanrio is:

we are going over to another ISP for our Internet/site connectivity access.

There 3 sites all with leased lines and a private network provided by ISP1

ISP2 are going to create another private network via another set of leased lines.

For a month, boss wants both networks running together beofre ISP1 gets switched off.

At the moment everyones default gateway points to the serial router of ISP1 at each site.

Boss says..lets make one of the meaty 3500XL 12 port as default gateway for all devices at each site, and then stick 2 default-gateway config lines on each of those switches pointing to ISP1 and ISP2 ..in his view packets can pick and choose which serial router to get out of ...

is he talking twaddle here??

[thisisshanky]

a 3500xl is not a layer 3 switch, so you can do routing on that box. In general, you can do as many default routes as you want, either with equal admin distance, or different admin distance as follows.

ip route 0.0.0.0 0.0.0.0 serial 0

ip route 0.0.0.0 0.0.0.0 serial 1

This will do load balancing on both serial interfaces. The type of load balancing depends on the type of switching configured on that interface.

Or, if you want to use a primary link (ISP1) and use ISP2 as backup,

ip route 0.0.0.0 0.0.0.0 serial 0

ip route 0.0.0.0 0.0.0.0 serial 1 150

[steve]

Cool!

but I have to put the IP addresses of the serial routers ethernet ports in place of serial 0 and serial 1 ?

Not bothered about load balancing as such..just want both routes out active and useable for a month, until we switch ISP 1 off.

by the way thanks for the prompt reply!

[jroyster]

If this is just a layer2 LAN (pcs into a switch) you can use GLBP or gateway load balancing protocol to use both gateways at the same time.

Or for failover HSRP would be used - one router would be the gateway and the other would just be waiting in case of a failure.

[thisisshanky]

Yes instead of serial interace, you should use ip addresses in your case. I guess you are not doing NAT on your end, as you have private IPs allocated by the ISP. Are they doing NAT for you on their end ?

[steve]

There is no NAT involved at our end...the ISP's routers at our sites have default gateway config lines pointing to our Firebox connected to another Internet gateway router on separate serial line..again all NATing if any done by ISP.

As I say this is just to be put in place to make sure our new ISP is able to cope and keep connectivity up better and more cheaply than ISP1

[fran]

The scene is the following.

The interface Gigabit 0/0 the ip connects to a router with the following configuration 83,175,204,2 with mask 255,255,255,224 and gateway 83,175,204,1

The interface Gigabit 0/1 the ip connects to a router with the following configuration 83,175,223,130 with mask 255,255,255,240 and gateway 83,175,223,129

The interface Vlan1 with direction IP 171,32,254,1 mask the users connect 255,255,0,0 themselves.

As they configure the gateway