We recently purchased some 3Com IntelliJack NJ225 switches:

alt text
(source: 3com.com)

The specification states that they support IEEE 802.1D, and a mandatory part of this standard is support for the rapid spanning tree protocol. However, we quickly realised that we could not safely create loops when connecting these devices together (using the four "front" ports). After several support calls, 3Com confirmed that they did not implement the RSTP.

I think it's fair to say that we're not using these switches for their intended purpose. But, did 3Com incorrectly claim support for IEEE 802.1D? Or is there a technical reason why these switches are exempt from implementing the RSTP?


3com are correct in the information you've provided. They specify support for STP (802.1D), but not RSTP (802.1W). RSTP is an extension of the STP spec which provides faster convergence.

They should still perform bridge loop prevention though. Just not as promptly as RSTP would. If they aren't functioning at all, then re-open the case.

  • I thought that, after 2004, RSTP completely replaced STP in 802.1D - perhaps these were released just before the 2004 version? Anyway, the switches do not generate any BPDUs so not even the STP is supported. The proprietary management software allows you to manually enable or disable ports - this is the only method of loop prevention I could find. – sblair Oct 19 '09 at 11:58
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    You're right, they were incorporated together in 802.1D-2004. It's possible that they could have either implemented 802.1D-1998 or something that just doesn't work at all. I've had some bitter experience with dodgy IEEE implementations on high-end 3com switches, so it wouldn't come as a complete surprise to me. I'd suggest re-opening the case and being firm but polite on a resolution. – Dan Carley Oct 19 '09 at 20:43

Dumb question, but you have checked that STP is enabled? These are managed switches.

I actually only enable STP on end-user VLAN's, I've just had 2-3x more failures of STP then failures STP could have saved me from.

My preference is actually MSTP, but vendor interoperability is a bit bad.

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    There's no option to enable (R)STP, on either the web interface or the management software. So I opened a support case, and 3Com eventually confirmed that they had not implemented STP (and mentioned that we might have bought the wrong device...). – sblair Oct 20 '09 at 20:48

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