Lan design with fiber and giga ports

Unanswered Question
Oct 6th, 2009

Hi all,

I am working on a design of a customer (banking system) LAN where the customer wants to have fibers between all switches and even servers (don't know any server accepting that but still looking for a solution...).

I have started the design and came up with a question about the max throughput of a SFP port when used to connect two switchs (3 meters) but couldn't find any answer on cisco's website.any idea ?

I am trying to compare that value with the Giga port throughput and see which design will be the most effective.

I guest that using fiber will spare me some security issues on the LAN.

Anyway I want to have your opinion on the design (see pict).

I have this problem too.
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Giuseppe Larosa Tue, 10/06/2009 - 01:55

Hello Paul,

I would look at the forwarding rate for the distribution switch


Forwarding rate:17.8 mpps (Cisco Catalyst 3750G-12S),

each GE port requires 1483000 pps per direction with smallest frames to be supported

so C3750G-12S supports roughly 6 GE ports full rate.

This can be acceptable.

Hope to help


Joseph W. Doherty Tue, 10/06/2009 - 03:44

You might want to know (I recall) 3750's don't support GLBP. However, they can be stacked. When you stack them, you can take the dual uplinks from the edge switches and configure them into a dual Etherchannel, with each link connected to different 3750 stack member. (BTW if the edge requires more than 48 ports, you might also want to consider the stackable 2975.)

The SFP port supports gig rate. This can be on fiber (or, if SFP-T supported, on copper). (BTW, you also have the option to Etherchannel such ports.)


BTW, believe forwarding performance requires 1.488 Mpps per gig Ethernet port. I.e. 3750G-12S's PPS rate supports wire-rate. (Also important is sufficient fabric bandwidth; 2x per port is needed. 3750 series provides 32 Gbps which is sufficient for up to 16 gig ports.)

Leo Laohoo Tue, 10/06/2009 - 14:20

I agree with Joseph regarding the 2975 instead of the 2960.

If the 3750 won't support GLBP then try a 6500E.

NOTE: I'm not sure if 3560E supports GLBP either. But if it does, look at the WS-C3560E-12D or -12SD. The 10gb ports support TwinGig converters.


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