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This is basically a shot in the dark. I have worked with many VoIP phones in the past, but not NEC phones. I'm not an NEC tech, but in this case, we are doing sub work for an NEC dealership.

Short version, I connected an NEC phone to a Cisco POE switch. After a few minutes, the Cisco switch rebooted. A few minutes after that it reboots again. Moved to a non-POE Cisco switch (same model) with a POE injector, same results.

IT's "just tell them something" answer is that it is an IP conflict. I doubt it. Same results 2 switches on 2 different networks. Dealer says that they talked to NEC support, and there are no known conflicts with Cisco switches. I asked another CIsco tech. He never heard of this before.

Before you say Broadcast Storm, I did not loop the connections. I only connected the LAN port, not the PC side.

I am not sure of the NEC phone model. I think that the NEC system is an SV9100

I have a Netgear switch in my truck when I go out today, but just curious if anyone has ever heard of anything like this. I have never heard of an IP device causing a switch to reboot like this before.

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Wow, that is bad! Even if you had a network loop or broadcast storm the switch shouldn't reboot. You'd think spanning tree would just shut the port down if there was a problem like that...

I've seen Cisco routers lock out an IP they don't recognize, but that's about the extent of the weirdness we've run into.

One other thing that has caused strange behavior on other switch brands is when you plug a VLAN capable (and active) switch port into another switch that's simply "dumb". On occasion this seems to cause an unintended bridge between VLANs and everything goes to crap.

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Originally Posted by Toner
Wow, that is bad! Even if you had a network loop or broadcast storm the switch shouldn't reboot. You'd think spanning tree would just shut the port down if there was a problem like that...

I've seen Cisco routers lock out an IP they don't recognize, but that's about the extent of the weirdness we've run into.

One other thing that has caused strange behavior on other switch brands is when you plug a VLAN capable (and active) switch port into another switch that's simply "dumb". On occasion this seems to cause an unintended bridge between VLANs and everything goes to crap.

I had another account where the Cisco switch would lock out a port when we connected a new VoIP phone. IT had to make some adjustments and all was good.

Another Cisco guy asked me if there was a dumb switch in the mix. Just the 2 Cisco switches is all there was. The 2 switches are not even connected together. Existing AT&T voip phones are on the POE switch

I assume a reboot is a panic response for something it didn't like. Very odd. I noticed the phone was searching for the switch and I believe it was doing LLDP query. Maybe I can look at the phone settings when I get there today to see if I can shut anything off.

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LLDP can certainly cause grief (wouldn't expect switch reboots though!) It's worth a try to shut off that option on the phone if possible.

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The first thing I do when signing into the VoIP phone for the first time is disable LLDP.
This helps to make the phone boot up quicker.

Last edited by dans; 12/02/21 12:45 PM.

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I disabled LLDP and statically set an IP address. I thought that might be the cure, but after about 5 minutes the switch rebooted again. I ran out of time so I threw in a Netgear POE I had with me. All working OK.

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Is it just one phone or several that are causing the Cisco to reset?

Have you tried using an external PSU for the phone?


Patrick T. Caezza
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How are you serving out your DHCP addresses?? I had a situation a couple of years ago where the SV9100 it's self used to randomly reset and we found that DHCP was being served from the PBZ and for some reason served two phones with the same address. When the second phone in the back of the reception area was used the SV9100 would reboot. After a lot of tooing and frowing between various sections of NEC , NECJ did admit that there was an issue with the DHCP address server on the SV systems that could in odd accessions serve up the same IP address. We changed the DHCP server to one that the customer used and the problem never happened again. Just a real left field observation.


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Paul W
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Have you added up your power consumption?

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For what it's worth we had a customer with a Cisco Switch that continuously gave IP Conflict alarms on the 9100. We never saw that before but after consulting with our IT department they suggested having the customers IT company turn off ARP probing on the Cisco Switch. The only time we have seen this is with Cisco Switch's. After that the alarm's went away.


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