No one good way to do this, depends on variables. Some commands may help
sh ip arp (only works if you have l3 interfaces in each vlan)
sh ip dhcp snooping binding (needs dhcp snooping)
sh ip device tracking interface gigabitEthernet
Showing posts with label cisco switch. Show all posts
Showing posts with label cisco switch. Show all posts
Tuesday, 12 December 2023
Thursday, 30 May 2019
PM-4-ERR_DISABLE link flap error detected when plugging in fibre on cisco switch
I was trying to connect two switches on different floors
lvl1 sw -> lvl2 sw
When I plugged in the fibre I could see the light was making it to the upstairs but when plugging the fibre cable into the switch on lvl2 the port was going into err-disable with the reason as link flap.
The cause of the issue was the wrong type of fibre cable was used in the fibre patch. Single mode cable was used. When my switch transceiver (10Gig-SR multimode) and fibre patches leads were OM3 multimode.
The core of single mode fibre is much narrower than multimode so they can't work together too much light (signal) is lost.
There are two fixes and both will probably cost you:
1 - re-run the fibre patch cables with multimode cable (OM3 or higher). Range is 300m so this is what is used inside most buildings. If you need a cable run longer then you have to use single mode.
2 - Buy single mode transceivers LRM and single mode patch cables. The single mode transceivers and cables are more expensive.
https://en.wikipedia.org/wiki/Single-mode_optical_fiber
lvl1 sw -> lvl2 sw
When I plugged in the fibre I could see the light was making it to the upstairs but when plugging the fibre cable into the switch on lvl2 the port was going into err-disable with the reason as link flap.
The cause of the issue was the wrong type of fibre cable was used in the fibre patch. Single mode cable was used. When my switch transceiver (10Gig-SR multimode) and fibre patches leads were OM3 multimode.
The core of single mode fibre is much narrower than multimode so they can't work together too much light (signal) is lost.
There are two fixes and both will probably cost you:
1 - re-run the fibre patch cables with multimode cable (OM3 or higher). Range is 300m so this is what is used inside most buildings. If you need a cable run longer then you have to use single mode.
2 - Buy single mode transceivers LRM and single mode patch cables. The single mode transceivers and cables are more expensive.
https://en.wikipedia.org/wiki/Single-mode_optical_fiber
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