[ale] 100 vs 10 Mbit problem

[Jonathan Rickman]

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. 

-- 
Jonathan Rickman
Key ID: 0DF501FF