OT: Network problem

[Neal Richardson]

  I needed to install a small hub in part of the build that was not on 
the network. When I connected the hub to the switch from the crossover 
port the whole network came crashing to the ground and the server locked 
up hard. Upon further investigation it turns out that the RJ45 jacks 
were wired complete wrong ( The old admin made the cable).
 
 My question is this:  Is this normal behavior to have the whole network 
go down due to a mis wired cable. I can understand the hub not working 
but to cause the whole thing to crash seams bizarre to me

Thanks
Neal