Do switches use the fastest route available between computers?

October 12, 2005 3:02 PM

I have 4 Gigabit switches for my network and one 10/100 router. Can/should I hook each switch up to the router and then also plug each switch into each other switch to improve internet performance while still maintaining Gigabit on my LAN?
posted by hoborg to computers & internet (5 comments total)

Unless you have very expensive managed switches, building loops by connecting the gigabit switches together AND to the router will cause problematic packet loops.

For maximum performance, you should connect the first GigE switch to the 10/100 router. Then you should connect each of the three remaining GigE switches to a port on the first switch. There should be only one connection to the router.

If you connect each GigE switch to a different 10/100 port on the router, you will have GigE speeds between machines on any GigE switch, but communication between two machines connected to *different* GigE switches will step down to 100mb to get through the router.

Switches should always be arranged in a tree topology. You can tell if your switches are configured safely if there is only one physical path between any two switches on the network.

A true router allows cycles to be created in the network. The things that are called "routers" and sold for home and small office networks are really protocol converters. They typically don't speak any of the protocols that allow large cyclic networks to be created, like BGP.

Just to add more confusion into the mix, many of the new expensive managed switches are also routers ("layer-3" switches). These things cost between $1000-$7000, so you don't often encounter them without also encountering a professional network admin.
posted by b1tr0t at 3:27 PM on October 12, 2005

No. Your internet connection is likely one to two orders of magnitude slower than your network. Nothing you do to your network will make the packets go out your router any faster.

Don't put multiple connections between switches unless you really know what you're doing.
posted by ldenneau at 3:28 PM on October 12, 2005

Three to five orders of magnitude if you are running GigE at home. Cable or DSL runs in the 1Mb/sec range, but often the remote site brings the aggregate throughput down to 100k/sec. GigE is 1000x faster than 1Mb/sec, and 10,000x faster than 100k/sec.
posted by b1tr0t at 3:35 PM on October 12, 2005

No, you should do what b1tr0t said. An ethernet segment is not supposed to contain loops, which is what you are proposing. Higher end hardware runs something called Spanning Tree Protocol, which basically turns off redundant ports to prevent loops. In that case, you'll get one switch connected to the router and the other three chained through it. But b1tr0t's configuration is much better.
posted by sbutler at 5:10 PM on October 12, 2005

I'm aware I won't get faster internet throughput, just thought I might get more efficient throughput. Thanks for the info; I knew it sounded too good to be true :P
posted by hoborg at 8:41 PM on October 12, 2005