[ale] 100 vs 10 Mbit problem

[Jeff Hubbs]

A few years ago, I had an issue - and it was with a Bay Networks switch,
too - where the switch wouldn't autonegotiate across the board and as a
result, our production Alpha cluster was only making 10 even though the
machines had 10/100 cards in them.

- Jeff

On Fri, 2003-09-12 at 21:19, Jonathan Rickman wrote:
> On Friday 12 September 2003 18:51, Dow Hurst wrote:
> > I have two machines with 10Mbit interfaces on a Baynetworks managed
> > 24port 10/100Mbit switch.  The other machines on the switch are
> > 100Mbit.  I am seeing collisions on the slower interfaces and having
> > trouble with large data transfers to and from those machines.  Is there
> > a solution to this problem that I can implement?  I haven't seen this
> > before even though I've had slow and fast ethernet interfaces on
> > negotiating switches before.  Should I change cables first, and try
> > different ports before anything else?
> 
> This actually was a very common problem back in the mid to late 90s when 
> 100baseT first started springing up. It is known as switch overload. The 
> problem is most likely the switch itself. Someone else mentioned adding a 
> second switch. If that works then it is definitely a case of switch 
> overload. What's happening is, you've got a firehose and a drinking 
> straw. The switch is a large funnel. The switch's memory pool is the 
> large conical part of the funnel and it can hold one gallon of water. The 
> switch's memory gets full and it starts discarding packets. Adding the 
> second switch adds another memory pool. It sounds to me like you have a 
> duplexing mismatch involved here as well. Stepping the 100Mb machines 
> down to HD will help a lot, but there is no ideal way to make this 
> problem go away. The choices are, slow everything down to the speed of 
> the slow machines, upgrade the switch fabric either by adding a second 
> switch or upgrading the existing switch, or put in a hub or slower switch 
> until you can get faster NICs for the slow machines. If you can manage 
> the switch on a per-port basis...set all ports to HD. When I ran into 
> this problem on a large scale, I ended up reverting to 10Mb switches in 
> several places just because visiting each workstation was not possible on 
> short notice. Balance is very important on switched networks. 
-- 
Jeff Hubbs <hbbs at comcast.net>