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Zaid Farooqui

3750E - 4507RE 10gig Fiber problem - help needed


we have a core switch 4507RE at the data center and 2 departments that connect to it via 10Gig fiber using X2-LRM modules.

Each department  has a 3 switch stack and both locations are identical w.r.t type and setup scenario ..  

the stack comprises of  1 x 3750E and 2 x 3750G . uplink is from X2 port tengig3/0/1 from the 3750E switch.

all of a sudden dept B started facing problem , where the ping would break and throughput comes around 6 - 7 mbps   from that dept to the server behind the core switch.   we also noted CRC error on both sides preodically ...   so ....

we replaced the multimode fiber patch cords, re did the splicing , which  stopped the CRC errors to appear.

now since morning the uplink port on the 3750E (3/0/1) would suddenly be in "down" state    with (err-disabled) as the status  when i run sh int ten 3/0/1

and i can also see CRC errors and input errors on the same interface..   if i do shut / no shut .. the port is up and active again..    but this has happned 3 times today..

the core swith side is still OK and no CRC / input / output  errors are seen..

now on the 3750E i have  swapped the 10gig module from 3/0/1 to 3/0/2 .  the port is still up but i can see 400 CRC and 500 Input errrors.....    

the module is also OK as i had replaced it with dept 1's module....

any anyone please suggest what and how to check ... im totally blank ..  which side has the problem ..... how to trace it

Glenn Matthys


Cisco X2-10GB-LRM

The Cisco 10GBASE-LRM Module supports link lengths of 220m on standard Fiber Distributed Data Interface (FDDI) grade multimode fiber (MMF). To ensure that specifications are met over FDDI-grade, OM1 and OM2 fibers, the transmitter should be coupled through a mode conditioning patch cord. No mode conditioning patch cord is required for applications over OM3. For additional information on mode conditioning patch cord requirements please see:

The Cisco 10GBASE-LRM Module also supports link lengths of 300m on standard single-mode fiber (SMF, G.652).

Also, with short distances, you might need an attenuator, otherwise the light sensors will be saturated and the module might overheat (which could lead to the errors you're describing and ultimately irreparable damage to the module).

Leo Laohoo
VIP Community Legend

CRC errors are detected by the switch in the RECEIVING end.  The switch doing the sending does NOT see CRC.  Therefore the errors could either be the LRM module or the line card of your 4500.