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Why do some 3rd-party SFP modules appear to not work in my ATI switch?

Why do some 3rd-party SFP modules appear to not work in my ATI switch?


Why would an SFP module that is known to work properly--i.e. tested successfully in lab equipment--not work in only my ATI switch?

TYPE OF SFP

Though it may sound too obvious to bother mentioning, it is a common mistake to use an SFP module that is not compatible with the required parameters of the connection.  Are you using a multimode SFP on a single-mode fiber link, or vice-versa?  Are you using a Gigabit SFP in an older switch that can support only 100FX or 100SX port speeds?  Are you using a 100FX SFP in a XEM12Sv2, which will operate at Gigabit speed only?  Are the fiber optic devices on both ends of the link configured identically--speed, duplex, optics, link negotiation, etc.?


PHYSICAL LINK ISSUES

Again, something simple here that can often be overlooked.  Has the fiber strand been tested end to end?  Have transmit and receive strands been rolled on one end?  If connected to managed devices, are the corresponding ports admin'd up on both sides?  One quick test to help isolate the issue is a fiber loopback.  Simply take a single strand of fiber and connect one end to the transmit port and the other end to the receive port of the same SFP.  Light transmitted from the SFP will loop back to its own receive port, and should therefore show link.  If so, then you know the problem is not with that SFP module or that switchport.


"SWITCHPORT LOCKED UP"

On occasion, an SFP port on an ATI switch can "lock up" in software.  In AlliedWare Plus devices you will see a log entry that looks like this:

2016 Nov  7 13:25:12 local6.crit awplus EXFX[1153]: SFP in port1.5.3 has locked up. Please remove.

This can occur when, for example, an SFP goes bad and needs to be replaced.  A local technician replaces the defective module without allowing sufficient time between removing the old one and inserting the new one.  Though SFP modules are hot-swappable, ATI recommends at least a 10 second gap between removing an SFP and inserting a new one in the same port, then giving another 10 seconds for the link to establish.  It is not unusual for field support to perform this action within only a few seconds timeframe.  Then, upon seeing the link not re-establish, reseat the SFP multiple times--within less than 10 seconds each time.  The SFP switchport will lock up, and will require the following procedure:
  • remove the SFP
  • manually shut down the switchport interface
  • wait at least 10 seconds
  • manually admin up the switchport
  • wait at least 10 seconds
  • insert the new SFP
  • wait at least 10 seconds
  • connect the fiber strand
If this does not fix the problem, then the relevant switchblade XEM/card will need to be reseated, or the switch will need to be rebooted.


VENDOR INTEROPERABILITY

Officially, *only* ATI SFP modules are fully supported in ATI switches.  Though Allied Telesis manufactures all its switching products to industry specifications/standards, and does not deliberately manufacture hardware to exclude interoperability with other vendor equipment, ATI product developers simply cannot perform interop testing with the vast number of products on the market.  Interop issues can even manifest as a result of a software upgrade--i.e. a 3rd-party SFP module was working just fine in an x908 running software 5.4.4, but then stopped working after the switch was upgraded to 5.4.5.  In these instances, 3rd-party SFP's should be replaced with ATI modules.
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