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New Member

Implementing Layer 3 backbone switching

Our organization is currently in the process of replacing our 3Com Corebuilder, layer 2, backbone switch with a Cisco Catalyst 6513. We want to take advantage of the 6513's layer 3 abilities and avoid having to send our interVLAN and internetwork traffic through our routers as it currently operates. Currently, our network's default gateway is a 3600 router. I'm wondering if I am going to need to change the default gateway of each of my network devices to be the IP address of the switch as it is now performing the internetwork routing.

Generally speaking, what should I be considering as we look to change from a layer 2 backnoned network to a layer 3 switch?

Thanks in advance for your thoughts and consideration. Any ideas would be appreciated.


Re: Implementing Layer 3 backbone switching

The best solution is to use the L3 switch as default as it switches packets faster than the 3640 can route. For best performance, you should indeed take care that the default gw adress matches the adress of the switch. The 3640 will be able to redirect the traffic if he knows the routes (by running a routing protocol) but this redirection is extra traffic that can be avoided.

You can consider to reconfigure the 3640 and make the switch use its IP adresses if changing all workstations is too much work. Normally this change would be achieved through DHCP and then it is not much work.



New Member

Re: Implementing Layer 3 backbone switching

Is it going to be one flat network or are you considering having multiple vlans on the Cat ? If that's the case, you could have ISL setup between the 3600 and the Cat , thereby enabling inter-vlan routing.

New Member

Re: Implementing Layer 3 backbone switching

You really want to get off the 3600 series and onto the 6513 for a few reasons. In your old one-armed router world all inter-vlan traffic had to traverse the 3600. In your new layer-3 switching world, you want to take advantage of the cut-through routing capabilites of the switch such that only the first packet of a conversation really hits the routing engine.

If your making use of DHCP the transition is quite a bit easier as all these parameters, gateway, dns, etc... can easily be changed en mass. We do DHCP for all workstations but servers are fixed, hard-coded addresses.

Btw - Welcome to my world! We cut over from the 3Com ATM to the Cisco 6513's a year ago. We used to have 7500's in our one-armed core.

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