VLANing vs Separate physical interfaces.

Unanswered Question
Mar 7th, 2008

I have a new 3845 router that comes with a 2-Gig ethernet interfaces and will replace an older router with dual ethernet interfaces. My dilemma is that my current production router has dual ethernet intefaces, one is dedicated for the production LAN and the other one is dedicated for a lab network. The new router's gig interfaces will be configured as follows; one inteface will be used for the outbound (Opt-E-Man) link and the other interface will be used for both the production LAN and the Lab segment via seprate VLANs.

My question is; is it better from a performace stand point to have separate VLANs and create interVALNs on the router or purchase a new spearate Gig card to install on the router and dedicate a separate interface for each segment.

I have this problem too.
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Joseph W. Doherty Fri, 03/07/2008 - 17:54

When you say inter VLAN, I assume you mean to trunk an interface on the 3845. If correct, you would be sharing the bandwidth and introduce some overhead dealing with the trunk.

In practice, since a 3845 has a 500 Kpps rating (or about 250 Mbps for 64 byte packets), it's likely you won't be able to overload a gig link. I.e. shouldn't be an issue sharing it.

Unsure of the impact of the VLAN trunk, but assuming your WAN link is effectively 100 Mbps or less, likely you'll have excess processing cycles. So, you might try with the VLAN trunk.


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