Cant get a simple 1 gig multimode fiber link to come up

[jdoebling]

I am going nuts. This is something that I do all the time. The last 2 times I have tried it, I had the same problem. HP Networking s7910 (like the 7500 switch, just before HP renamed it). going from a 1gig SFP gbic to another 1gig SFP Gbic - IN THE SAME ROOM.

Read this before replying and telling me to swap the connectors on one end of the link....

Here is what I've tried:

1. Different fiber patch cables
2. Different GBICs in our core
3. Different PORTS in our core
4. I can loop the Core side & I get a link
5. I can loop the Comcast side & I get a link
6. I tried forcing the speed to 1gig on the Core side (but that shouldn’t impact a physical link)
7. I can get a link from the WAN port on the Core to another GBIC on the core switch
8. The Comcast box always gets a link when connected to the core, Our side does not.

I can see red light coming from the Comcast GBIC.
I can see red light coming from the Core GBIC.
I made sure the red light coming from us goes to the dark side on the Comcast Box.

 

[jdoebling]

Here is the Answer:
Even though its just a physical link, the 3Com/HP Networking A-Series to <any-other> requires a hard coded speed AND DUPLEX setting before the link light will come on.

For a 1Gig, full duplex connection:

Interface Gigabit n/n/n
port access vlan xxx
speed 1000
duplex full

Other switches will show a link light when they see light from the other side in the right wavelength.

 

[VinceWhirlwind]

Yes, you get no physical connectivity unless you set both sides to 1000/Full instead of auto.

Unless you're using 1Gb SFPs in SFP+ slots, in which case it only works if set to auto(!).