c3845 & SFP 1000BaseLX modules

Well we had a scheduled planned event wherein we had to connect a Single Mode Fiber to the SFP module on the gi0/0 of the c3845.

Sounds simple,
well its simple
1) insert the SFP, the router immediately recognizers it.
2) configure the interface with followings details

• media-type sfp
• duplex
• speed
• no shut
• IP address

Well we did all the above and yet the link was not coming up.

We could also not see the SFP LED indicator come UP. This clearly indicated that there was a link issue .What could we've done wrong ?

Seems to be a pretty simple task, aint it ?

Well it turned out to be a horror for us.

We spent hours on the testing the Fiber , the config, and the SFP itself.

To our horror, out some searching on cisco.com & goggle we found out that we should try the defaults first.

i.e default speed

&

default duplex

So we did that , not hoping much luck.

But surprisingly the link came Up instantly

the LED on the SFP module was glowing & we could ping the remote destination address as well.

So I am not sure, why did the Link not come up when we had enforced the Duplex = Full & Speed = 100 , also tried Speed = 1000 ?

Anybody can help why it didn't work ?

the present interface config is as follows:-

interface GigabitEthernet0/0

IP address 10.12.13.9 255.255.255.252

IP access-group 112 in

duplex auto

speed auto

media-type sfp negotiation auto

end