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Mixed speed network question

Last response: in Networking
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January 27, 2012 9:23:42 AM

Good day to all,

I have a simple "yet-difficult-to-persuade-colleagues" question to ask those in the know...

We are busy setting up a WAN between two buildings: For shorter description Building A = A and building B = B.

The proposed solution is this:

A has network infrastructure consisting of the following:

Server farm running on Gigabit backbone off a HP 3500 Distro switch with 1 GB uplink, the rest of the ports are 100 MB
LAN infrastructure is CAT5

B has basically the same setup as A as far as infrastructure is concerned with a HP 2650 switch supporting 1 GB uplink and the rest of the ports are 100 MB.


My question/argument is this:

If we run a Optic fiber between A and B to the respective switches we will not have the benefit of 1 GB technology due to the fact that we are delivering to our clients at only 100 MB. My understanding is that the slowest hardware component brings the speed down to its own capability, in other words eventhough we have 1 GB link between the switches the speed will be reduced to 100 MB when a "request" from a 100 MB client is sent to the servers from B to A. Am I correct with this assumption?

Thanking you in advance for clearing this and maybe helping me to win a wager....

:) 
January 27, 2012 4:06:40 PM

You are correct. You would get GB speeds (or thereabouts) between the switches but the weakest link is the connection from the switch to each client.

If you link the switches with only 100MB link then want to upgrade each clients' connection later you will bottleneck from the 100MB and nothing short of replacing the connection will get you any faster transfers.

One other thing to consider, If you have say 8 clients all communicating from A to B then you will still have this bottleneck unless you go with a GB connection. Think about it this way: with a 100Mb connection, only one client could use the entire 100Mb bandwidth at a time and if you have multiple clients trying to do the same, each would get a portion of that bandwidth.
January 30, 2012 8:09:27 AM

landran said:
You are correct. You would get GB speeds (or thereabouts) between the switches but the weakest link is the connection from the switch to each client.

If you link the switches with only 100MB link then want to upgrade each clients' connection later you will bottleneck from the 100MB and nothing short of replacing the connection will get you any faster transfers.

One other thing to consider, If you have say 8 clients all communicating from A to B then you will still have this bottleneck unless you go with a GB connection. Think about it this way: with a 100Mb connection, only one client could use the entire 100Mb bandwidth at a time and if you have multiple clients trying to do the same, each would get a portion of that bandwidth.



Hi landran,
Let me get this straight, eventhough we have a GB connection between switches we are brought down all the way to 100 MB because of slowest link rule? Thus, the speeds between A and B would be the same whether we had a GB link or a 100 MB link?

thanks
Spyrex
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January 30, 2012 12:47:28 PM

landran is correct, the GB link will work at GB speed but because the next leg is only 100mb the switch will que some of the packets but eventually slow down the link so it is not overloaded.
January 31, 2012 6:07:10 PM

spyrex said:
Hi landran,
Let me get this straight, eventhough we have a GB connection between switches we are brought down all the way to 100 MB because of slowest link rule? Thus, the speeds between A and B would be the same whether we had a GB link or a 100 MB link?

thanks
Spyrex


I think you have misread landrans comment. He said if you only had a 100mbit connection between routers it will be a bottleneck In his example, he has 8 clients running at 100Mbit = 800Mbit potential. 800 > 100 = fail. If you have a gigabit (1000Mbit) connection between routers and those same 8 clients, you will still have 200Mbit overhead between the routers, 1000mbit - 800 = 200, and since 1000 > 800 you won't have a bottleneck.
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