Fiber problem

[DRGL]

Hi,i have a customer with a fiber link between two buildings(about 160M) with a switch at each end,all of the servers at one end(main building) connect to a switch with in biult fiber module(via cat5e cables),at the other end is a switch also with in built fiber module serving 11 PC's(via cat5e 10/100 cabling).All the PC's in the main building are operating nice and fast,the machines at the remote end are really slow.We didn't install the fiber so the spec. is unknown.Does this sound like faulty fiber and/or fiber module(s)?? How many PC's can be connected via a fiber link with no slowdown??(via a switch connecting to 10/100 cat5e network) The servers are connecting to the main switch via 10/100 cat5e cables,i guess this also could be an issue??(Surely the servers should connect via 1Mbit fiber??)any help and info would be great guy's.....Dave

 

[DRGL]

opps,i meant the servers should connect via 1 Gigabit!! not 1 Mbit....

 

[jimbopalmer]

I have a long rant claiming to be a FAQ in the ethernet forum on this but I will recap.

If you get connectivity over fiber (pings work) but horrible thoughput (file transfer is slow) suspect duplex mismatch

If one side is speaking half duplex while the other side is speaking full duplex throughput is about 1000 times worse than it should be.

Fiber (almost) never has an Auto speed/Duplex mode, you have to set it.

If the servers show they are saturated on the network, they can be 'faster' with a faster NIC

I tried to remain child-like, all I acheived was childish.

 

[DRGL]

AFAIK both switches are set to full duplex,i know for sure one end is,at the main building end is a Cisco switch,what's the best way to check it's duplex setting?? There are no user manuals with it.

 

[jimbopalmer]

I am not a Cisco switch user, so I do not know the commands, but it either has to be full or half.

If you try setting the known full side to half, and throughput goes up, then you know the Cisco side was set to half. Later when you get the commands to set the Cisco to full, you set the known end back to full.

(recalling that while full may approach twice as fast as half, a mismatch is 1/1000 as fast)

I tried to remain child-like, all I acheived was childish.

 

[lui3]

Cisco commands for checking duplex

login into the terminal via telnet or console

commands are

show interface

or

show interface summary

You may have to read through the output and find the field with duplex indications.

 

[DRGL]

thanks for the help,i'll give it a try.......

 

[Bobg1]

You really should find out what the specs are on the fiber.
Is it single or multi mode? Are both switchs the same? Are the fiber modules the same? What fiber should be used with them?
A mismatch between the fiber and the modules can cause problems.

 

[DRGL]

AFAIK it was all working fine............

 

[jimbopalmer]

In my experience, mismatched speed or wrong interface for the cable will prevent any communication, to get communication but very low throughput is a duplex issue.

On my notrel switches it is frequent at 100 Mbps (they default to half) but rare at gig. (they default to full)

I tried to remain child-like, all I acheived was childish.