Network Design: Extention to 12 ethernet switches

Answered Question

We have the following configuration:

8 x WS-C3550-24-SMI Switches in the following configuration:


(C3550)--GigaStack---(C3550)--Gbic Fiber---(C3550)--GigaStack--(C3550)--Gbic Fiber--(C3550)--GigaStack--(C3550)--GigaStack--(C3550)--Gbic Fiber--(C3550)

There are versatile vlan created in this configuration (#5)



1) Is it correct that we cannot extend more than 9 switches in this way?


In the future we want to use routing to smaller our broadcast domains etc, but in the meanwhile we would like to extend this configuration with 4 more switches coupled by Gbic Fiber modules.


2.) Can we use a WS-C3550-12G (10 Gbic ports and 2 10/100/1000BaseT ports) to extend to 12 Switches in the following configuration?


(WS-C3550-12G )

| | | etc..

(C3550) (C3550) (C3550)

|

(C3550)


3.) What do you recommend to use for extention with minimal cost?


Thanks in advance

Correct Answer by konigl about 14 years 3 months ago

Leo,


Are you using the GigaStack GBICs as low-cost point-to-point connections between two switches? Or are you using them in the classic GigaStack cascaded configuration?


The way I read your description of the network design, I see dedicated point-to-point connections; and no GS GBIC has more than its hosting switch and one other switch connected to it, like this:


3550#1 to 3550#2 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#2 to 3550#3 using two SX GBICs, GigEth0/2 to GigEth0/2

3550#3 to 3550#4 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#4 to 3550#5 using two SX GBICs, GigEth0/2 to GigEth0/2

3550#5 to 3550#6 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#6 to 3550#7 using two GS GBICs, GigEth0/2 to GigEth0/2

3550#7 to 3550#8 using two SX GBICs, GigEth0/1 to GigEth0/1


If this is how your switches are configured, then you do not have a theoretical limit to how many you can continue to add in this fashion. You will find for performance reasons, though, that it is not the most balanced topology. If your servers are located on one of the end switches, then the further your client computer is from that switch, the more traffic it will have to contend with to get to that server. Generally speaking, in this scenario the optimum place to put your servers would be somewhere in the middle, so the client computers have a fairer chance of reaching the servers.


A better design for improved performance is to have each of the 3550 switches directly connect to a 3550-12G. This minimizes the number of switches each client computer must go through to reach a server; and you can put key servers right on the 3550-12G, so everyone will have equal access to them. You can also use the 3550-12G to do your Layer 3 switching of TCP/IP between your VLANs at wire-speed, it's got the Enhanced Multilayer Image software already loaded.


If you are using, or thiking about using, the GS GBICs in a classic GigaStack cascaded configuration, you are limited to nine in the stack. That configuration would look something like this:


3550#1 to 3550#2 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#2 to 3550#3 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#3 to 3550#4 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#4 to 3550#5 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#5 to 3550#6 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#6 to 3550#7 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#7 to 3550#8 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#8 to 3550#9 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#9 back to 3550#1 using a GigaStack cable, GigEth0/1 to GigEth0/1


GS GBICs not being used as point-to-point, but rather being used as GigaStack cascades, operate in half duplex instead of full duplex mode. This cuts into overall network performance, but if you are using this configuration then connectivity and cost were the overriding factors.


If performance is the overriding factor, then the 3550-12G as a backbone or aggregator makes more sense. If you have all the GS and SX GBICs I mentioned earlier in this post, then all you will need to purchase is the 3550-12G distribution switch.


Hope this helps.

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Prashanth Krishnappa Tue, 05/13/2003 - 18:27
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Yes..The maximum supported number of switches in a gigastack is 9. Yes you can use a 3550-12G switch as an aggregator. Lot of customers use it for similar reasons

Correct Answer
konigl Tue, 05/13/2003 - 20:08
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Leo,


Are you using the GigaStack GBICs as low-cost point-to-point connections between two switches? Or are you using them in the classic GigaStack cascaded configuration?


The way I read your description of the network design, I see dedicated point-to-point connections; and no GS GBIC has more than its hosting switch and one other switch connected to it, like this:


3550#1 to 3550#2 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#2 to 3550#3 using two SX GBICs, GigEth0/2 to GigEth0/2

3550#3 to 3550#4 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#4 to 3550#5 using two SX GBICs, GigEth0/2 to GigEth0/2

3550#5 to 3550#6 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#6 to 3550#7 using two GS GBICs, GigEth0/2 to GigEth0/2

3550#7 to 3550#8 using two SX GBICs, GigEth0/1 to GigEth0/1


If this is how your switches are configured, then you do not have a theoretical limit to how many you can continue to add in this fashion. You will find for performance reasons, though, that it is not the most balanced topology. If your servers are located on one of the end switches, then the further your client computer is from that switch, the more traffic it will have to contend with to get to that server. Generally speaking, in this scenario the optimum place to put your servers would be somewhere in the middle, so the client computers have a fairer chance of reaching the servers.


A better design for improved performance is to have each of the 3550 switches directly connect to a 3550-12G. This minimizes the number of switches each client computer must go through to reach a server; and you can put key servers right on the 3550-12G, so everyone will have equal access to them. You can also use the 3550-12G to do your Layer 3 switching of TCP/IP between your VLANs at wire-speed, it's got the Enhanced Multilayer Image software already loaded.


If you are using, or thiking about using, the GS GBICs in a classic GigaStack cascaded configuration, you are limited to nine in the stack. That configuration would look something like this:


3550#1 to 3550#2 using two GS GBICs, GigEth0/1 to GigEth0/1

3550#2 to 3550#3 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#3 to 3550#4 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#4 to 3550#5 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#5 to 3550#6 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#6 to 3550#7 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#7 to 3550#8 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#8 to 3550#9 using one more GS GBIC, GigEth0/1 to GigEth0/1

3550#9 back to 3550#1 using a GigaStack cable, GigEth0/1 to GigEth0/1


GS GBICs not being used as point-to-point, but rather being used as GigaStack cascades, operate in half duplex instead of full duplex mode. This cuts into overall network performance, but if you are using this configuration then connectivity and cost were the overriding factors.


If performance is the overriding factor, then the 3550-12G as a backbone or aggregator makes more sense. If you have all the GS and SX GBICs I mentioned earlier in this post, then all you will need to purchase is the 3550-12G distribution switch.


Hope this helps.

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