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Adding a 3550-12T to (4) stacked 3548G's?

We are looking at adding a 3550-12T to our existing GBIC linked 3548s - to establish a gig backbone for (9) LAN servers.

Can anyone suggest how best to physically connect the (4) stacked 3548s to the new 3550-12T?

Should I use a redundant loop? The 3548s are looped now - but i've heard mixed things about redundant looping.

It may be that there is only one way to do this, but I thought I'd check to see if anyone can suggest a best configuration.

Does look like it will work?

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Re: Adding a 3550-12T to (4) stacked 3548G's?

Do you have one GigaStack GBIC per 3548 switch? I will assume so, for the following discussion.

Optimally, break up the stack and give each 3548 a single point-to-point Gig connection to the 3550-12T. That takes up four of the twelve interfaces.

Is there a LAN server that predominantly serves up to 48 users that can all be grouped onto one 3548? If yes, then plug it directly into the second Gig interface on that switch; plug the remaining eight servers into the 3550-12T. If no, then plug the least-accessed Gig server into the second Gig interface on any 3548 switch, and plug the other servers into the 3550-12T. Either way, you have fully populated the ports on the 3550-12T.

If you choose to keep using the GS GBICs, the four you have will get two of the 3548s connected; you will need to purchase three additional WS-G5483 1000BASE-T GBICs to connect the other two 3548s and that one Gig server. (If you want to get rid of the GS GBICs, you will need to buy four more TX GBICs, for a total of seven.)

Less optimally, but perhaps more realistic, plug the nine Gig servers into the 3550-12T. Then tie in two 3548s to the GBIC slots of the 3550-12T using the four GS GBICs; purchase four more GS GBICs and daisy-chain the remaining two 3548s off the second Gig interface of the already-connected 3548s.

Looping the GS GBICs, or using both ports on the GS GBIC, puts them into half-duplex mode I think. Not the best thing for a performance.

If performance out of the 3548s is not that big of a concern, then you could get by with purchasing only two more GS GBICs, and create a looped stack of two 3548s out of each GBIC slot of the 3550-12T.

Hope this helps.

New Member

Re: Adding a 3550-12T to (4) stacked 3548G's?

Your reply helps tremendously. Thank you. I just need a little clarification. (Yes I have one GS GBIC per switch).

1. Do I need to have the users of the LAN server (that is isolated to one one of the free GBIC slots of one of the 3548s) on the same 3548 so that the bandwidth is best utilized? What happens when a user that is not on the same 3548 tries to access that LAN server? Is it just a slower connection?

2. If I follow the suggested optimal setup - is it full duplex? If I use the less optimal setup, is it then half duplex? Is half duplex much slower when in gig mode? It's hard to find any real world definitions on the differerence between full/half dup gig.

3. If I go with the "Less optimal but more realistic" option, is it less otpimal due to less bandwidth/throughput?

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