Design Question for Default Route

Unanswered Question
Apr 6th, 2010

Hi,

Our network topology consists of 6 3560G switches, interconnected with fiber. The SFP ports are defined as trunks.

We have 5 vlans defined on the network.

The WAN links are connected to a 2811 router with an added NME Gigabit card (10.2.100.1). HEre are thr routes defined on the 2811

ip route 0.0.0.0 0.0.0.0 x.y.z.0 50
ip route 0.0.0.0 0.0.0.0 10.12.14.1 100
ip route 0.0.0.0 0.0.0.0 192.168.100.1 200
ip route 10.2.100.0 255.255.255.0 10.2.100.2
ip route 10.2.120.0 255.255.255.0 10.2.100.2
ip route 10.2.130.0 255.255.255.0 10.2.100.2
ip route 10.2.135.0 255.255.255.0 10.2.100.2
ip route 10.2.150.0 255.255.255.0 10.2.100.2

One one of the 3560G switches (10.2.100.2) we have our vlans defined and a default route pointing to the router at 10.2.100.1. In addition each 3560G switch has Vlan1 defined with an ip address in Vlan1. On these 5 switches we have ip routing defined.

Questions:

-Do we need a defualt gateway defined on each of the remaining 3560G switches?

-If we do need a default gateway defined, should it be the 'core' 3560G switch at 10.2.100.2, or the NME card in the 2811 router (10.2.100.1)?

TIA

I have this problem too.
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The question asked was "do we need" and as far as "need" goes i don't think you have mentioned anything that would require this to happen.

With that said I shoudl mention that without a defined gateway you could experience 2 common issues:

1) routes can break, generally during a partial outage, without a default gateway.

2) monitoring switches can often be a problem when the switch doesn't have a default gateway

There may be more reasons, but those are the two I most commonly see.

Assign the defualt gateway with the strongest path possible, treat it as your "when all else fails do this".  I would test the default gateway before and after with a simple ICMP up/down monitor. Make sure your ICMP test has at least 1 broadcast domain seperation so the switch can't find it on it's own and is forced to use the default route.

Jon Marshall Tue, 04/06/2010 - 11:55

Charles

Questions:

-Do we need a defualt gateway defined on each of the remaining 3560G switches?

-If we do need a default gateway defined, should it be the 'core' 3560G switch at 10.2.100.2, or the NME card in the 2811 router (10.2.100.1)?

If you have routing enabled on all the 3560 switches then you should not define a default-gateway at all, you should define a default-route and this could be either. If the switches are L2 only then you would define a default-gateway and it would be the vlan 1 IP address on the core 3560G switch.

Jon

IM-Design Fri, 04/09/2010 - 13:56

I think the switches are all L2 only - how can I tell?

Also, I think I mis-spoke earlier. We don't have defualt-gateway defined, rather we have a default route 'ip route 0.0.0.0 0.0.0.0 10.2.100.2'.

Thanks for your help!

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