Traffic across VLANs when using vtp

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Apr 25th, 2007
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Hello. I was wondering what happened to traffic when it traverses VLANs that are being distributed using vtp.


For instance, say our core switch is a 4507R, with a 48 port line card, and it is the vtp server. It has three vlans on it, ip address 192.168.1.x (VLAN 10), 192.168.2.x (VLAN 20) and 192.168.3.x (VLAN 30), and traffic is routed around the subnets using inter-vlan routing.


Now, say we add a stack of 3750E's. They are trunked using a 4 interface etherchannel (one into each member of the stack). This stack will be the vtp client.


My question is, will servers plugged into each of the different vlans on the stack need to go back to the core through the etherchannel trunk in order to communicate with each other, or will the traffic stay local on the stack?


Does that make any sense at all? I can post a diagram if it doesn't.

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sundar.palaniappan Wed, 04/25/2007 - 10:01
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VLANs propagated via VTP and inter-vlan routing are separate functions. For servers connected to the 3750 stack and belonging to different VLANs to be able to talk to each other the traffic would have to go through the 4507 as that's the layer3 gateway for the respective VLANs.


HTH


Sundar

poulid Wed, 04/25/2007 - 10:18
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OK, thanks. So I guess the only way to get the traffic to stay local to the stack is by moving the layer 3 gateways to the stack, and do the inter-vlan routing there, right?

Jon Marshall Wed, 04/25/2007 - 10:39
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Hi


Yes, or if you can place the servers that need to communicate with each other within the same vlan.


HTH


Jon

poulid Thu, 04/26/2007 - 05:41
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Thanks. Would you recommend uplinking into the core 4507R from the stack using a L2 ether-channel trunk, or a L3 route?

Jon Marshall Thu, 04/26/2007 - 05:50
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Hi


If you are doing the inter-vlan routing on the 3750's then i would use L3 uplinks.


L3 will give you equal cost paths to the core, very quick failover with little packet loss and will eliminate spanning-tree off your uplinks.


HTH


Jon

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