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New Member

3Com and Cisco GBIC compatability ?

Dear all,

We are looking at installing 2 x Catalyst 2950G-48EI Switches at the Edge. These will be connecting to a 3Com Corebuilder 9400.

One of these will run a single LX GBIC that connects to a 3Com SX GBIC on the Corebuilder. The second will run two SX GBIC's (trunked) that connect to two of the fixed GB ports on the Corebuilder.

Does anybody know of any compatability issues between Cisco LX/SX GBIC's and 3Com GBIC's/Corebuilder ?



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New Member

Re: 3Com and Cisco GBIC compatability ?

The connections must be LX/LH to LX/LH or, SX to SX. You can't use LX/LH to SX.

Other than that, they should work ok.


Re: 3Com and Cisco GBIC compatability ?


As JSessler said, match up your interfaces. This is important because of the wavelengths used for transmission. SX GBICs use 850nm, LX/LH GBICs use 1300nm. So the Cisco LX/LH will NOT talk to the 3COM SX -- incompatible wavelengths.

The wavelengths interact with fiber optic cable types in different ways, resulting in different maximum transmission distances. So it's important to know what kind of fiber you have, too. SX optics are rated for multimode fiber only (either 62.5/125 or 50/125-micron) and are limited to 220-275m runs.

LX/LH optics can also use MMF but need mode conditioning patch cables at both ends of fiber runs that are over 250m and up to to 550m in length. LX/LH normally use SMF and the 1000BASE-LX standard specifies out to 5km, but most manufacturers rate their optics out to 10km.

If you must use a Cisco LX/LH GBIC over appropriate fiber as noted above to a 3Com SX port, you will need a media converter at the 3Com side to take the signal from 1300nm to 850nm. Transition Networks ( is one company that makes these. Or, you could get a 3Com LX GBIC: CB9400 had 12 fixed SX ports and slots for 12 GBICs; if you still have a slot available, that's the way to go.

For the 2950G-48EI that will run two SX GBICs (trunked) to the CB9400, make sure the Cisco switch is set up to do LACP-based 802.3ad link aggregation and not Cisco's proprietary EtherChanneling.

Also, there's a negotiation setting that you may need to disable on the Cisco Gigabit port, to allow it to communicate properly with the 3Com. I don't remember what it is at this moment, it's been a while since I had to do this; but I do remember I had to do something. Some others have encountered similar problems with Dell switches and have posted here. Search here for "Dell" should help you find it.

Hope this helps.

New Member

Re: 3Com and Cisco GBIC compatability ?

Many thanks for both replies !

New Member

Re: 3Com and Cisco GBIC compatability ?

FYI. These 3com gig nics are rather particular. I just went about 10 rounds with one b/c it couldn't connect. I suggest that when you are ready to implement double and then triple check the nic settings. It will save you a world of headache.


New Member

Re: 3Com and Cisco GBIC compatability ?

I have seen some issues where you getan error message on the cisco. But if you disable CDP on that interface it goes away and works ok