Got overlapping gateways in one vlan of cat6509. Howto solve

Unanswered Question
Aug 10th, 2007

I have a catalyst 6509 with an interface vlan that exists of an ip address and multiple secondary addresses, some of the secondary addresses are in the same subnet, so for one subnet there are multiple gateways. Is there a way to find out which default-gateway is used by which client, without checking it on the clients.

I think sniffing in the vlan on the destination address would be one option, but are there other options, i would like to have a clean situation, there are maybe gateways that aren't justed anymore ?



I have this problem too.
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Pavel Bykov Fri, 08/10/2007 - 03:22

We had this exact problem too. Unfortunately there is no easy way to find this out.

Clients use default gateway when destination is in different subnet than their own IP address, so there is no extra communication to differentiate default gateway (Presumably we are talking about static clients, i.e. no DHCP).

One option is to sniff for the destination MAC address of the gateways in a period of load (some load is enough,), if it used a lot or not.

Remember that packet destination IP address will be that of a final destination, not of the Default Gateway. There will be MAC address of the Default Gateway and IP address of the actual destination.

pbogaerts Fri, 08/10/2007 - 07:02

Problem is with static client.

It is true that it should be the mac-address, but i have looked on the mac address, and this seems always the same for all the addresses main and secondary on the same vlan interface.

Any ideas ?


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