Multiple default gateways

[alanchia2000]

Hi,

I have two "non-cisco" gateways connected to Cisco 3750, and have define routes to two default gateways.

ip route 0.0.0.0 0.0.0.0 192.168.1.254

ip route 0.0.0.0 0.0.0.0 192.168.1.253 200

My question is after entering the floating route, it seems to disappear. Is it normal?

If 192.168.1.254 goes down, does the floating route take over?

[amit-singh]

Hi,

You wont see this route ip route 0.0.0.0 0.0.0.0 192.168.1.253 200, in routing table when you do a show IP route as this route has more AD. Router will install the best route only in its routing table. However this would be listed in sh run and you will be able to see it.

Yes, your floating static route will take over once the main gateway goes down.

HTH,

-amit singh

[milan.kulik]

Hi,

IMHO, it will not work.

Your router will not notice that the 192.168.1.254 has gone down.

I suppose both 192.168.1.254 and 192.168.1.253 are connected via the same ethernet interface (correct me if I'm wrong).

In this case the 3750 is only able to notice the interface has gone down, but not a particular gateway has gone down.

Regards,

Milan

[alanchia2000]

Given scenarios:

Scenario 1:

____192.168.1.254--

|

Sw 1 (3750)

|

Trunk (3550)

|

Sw 2

|_____ 192.168.1.253

192.168.1.254 is connected to Sw 1

192.168.1.253 is connected to Sw 2

On Sw1

ip route 0.0.0.0 0.0.0.0 192.168.1.254

ip route 0.0.0.0 0.0.0.0 192.168.1.253 200

Does floating route take over if 192.168.1.254 goes does?

Scenario 2:

__eth0__192.168.1.254--

|

Sw 1 (3750)

|_eth1____ 192.168.1.253

192.168.1.254 is connected to Sw 1

192.168.1.253 is connected to Sw 1

on Sw1

ip route 0.0.0.0 0.0.0.0 192.168.1.254

ip route 0.0.0.0 0.0.0.0 192.168.1.253 200

What if I connect 192.168.1.253 to Sw1 instead? Would floating route take over if 192.168.1.254 goes does then?

[amit-singh]

Yes, Milan is absolutely right. I am sorry , my mistake I didnt check the 2nd gateway IP. It seems like what Milan is assuming and it will not work in that case.

Thanks, Milan for your reply. I will take care of such little mistakes from next time.

Thanks,

-amit singh

[Richard Burts]

Milan's comment that the router would not know if the next hop address through an Ethernet interface became unavailable reflects the way it used to be. Cisco has introduced a new feature of object tracking and it is possible to use this with static routes to get the operation that the original post wants.

This link is a good source of information about Reliable Static Routes using Object Tracking.

http://www.cisco.com/en/US/products/sw/iosswrel/ps5413/products_feature_guide09186a00801d862d.html

HTH

Rick

[alanchia2000]

Rick, the solution you proposed is not supported on Cisco 3750. I cannot seemed to find "track" key word in ip route

ip route 0.0.0.0 0.0.0.0 192.168.1.254 track 123

[milan.kulik]

Hi Rick,

AFAIK, Object Tracking is not supported on L3 switches like Cat3750s and 3550s.

So I'd suggest using some fast convergence dynamic routing protocol between the 3750 and that two gateways.

OSPF would be probably a good choice (as the gateways are non-Cisco, so EIGRP can't be used). If configured properly (to include only the lines between that three routers), it should not consume so much resources on the routers.

Regards,

Milan

[Richard Burts]

It is a fairly new feature and there appear to be more platform dependencies than I realized.

In general I like the idea of a fast converging routing protocol. But without knowing a bit more about the devices that the 3750 is connected to I am not sure if it is practical to run OSPF. For one thing if OSPF is running then LSAs that are advertised from one neighbor will be learned by all neighbors. Especially if these gateways are provider devices then sharing advertisements would not be good.

I wonder if it would be possible to run OSPF with one gateway and arrange for that gateway to advertise only a default route. And to set up a floating static pointing to the other gateway.

HTH

Rick