Cisco switch: trunk port MAC address disappears from MAC address table
I have users complaining of slowness on their machines but we can't find anything specific (ping tests, etc). I'm trying to rule out the connection between the switch they're plugged into (3560) and the core switch (a stack of 3570s).
Currently the 3560 has one fiber connection trunked back to core switch. When tracing the trunk port back through the network I run into the odd issue of the MAC address of the 3560's trunk port disappearing from the MAC address table in the core switch. In the output below Switch1 is the core switch stack and Switch4 is the switch I'm investigating.
Switch4#sh int tru
Port Mode Encapsulation Status Native vlan
Gi1/2 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi1/2 1-4094
Port Vlans allowed and active in management domain
Gi1/2 1-2,30,40,42,50,60,70,72,8
Port Vlans in spanning tree forwarding state and not pruned
Gi1/2 1-2,30,40,42,50,60,70,72,8
Switch4#sh int gi1/2
GigabitEthernet1/2 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is XXXX.dbd3.f0b2 (bia 30e4.dbd3.f0b2)
Confirming which port is trunked back to Switch1
=======
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
The mac address shows up when I search for it
Switch1#sh mac address-table | inc f0b2
Switch1#sh mac
The mac address doesn't show up suddenly
Switch1#sh mac address-table | inc Gi2/1/3
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
1 XXXX.480e.2751 DYNAMIC Gi2/1/3
40 XXXX.11a0.5372 DYNAMIC Gi2/1/3
70 XXXX.5f0e.a116 DYNAMIC Gi2/1/3
80 XXXX.b6da.d050 DYNAMIC Gi2/1/3
100 XXXX.dbd3.f0c1 DYNAMIC Gi2/1/3
The mac address shows up in the table now
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
The mac address shows up when I search for it again
Switch1#sh mac address-table | inc f0b2
Then it doesn't
Switch1#sh mac address-table | inc Gi2/1/3
1 XXXX.480e.2751 DYNAMIC Gi2/1/3
40 XXXX.11a0.5372 DYNAMIC Gi2/1/3
70 XXXX.5f0e.a116 DYNAMIC Gi2/1/3
80 XXXX.b6da.d050 DYNAMIC Gi2/1/3
100 XXXX.dbd3.f0c1 DYNAMIC Gi2/1/3
And it doesn't show up in the mac address table now
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
Now it's back
Can anyone explain why this behavior is going on? I've checked on a few more trunk ports between my switches and I don't run into the "disappearing mac address" issue.
Currently the 3560 has one fiber connection trunked back to core switch. When tracing the trunk port back through the network I run into the odd issue of the MAC address of the 3560's trunk port disappearing from the MAC address table in the core switch. In the output below Switch1 is the core switch stack and Switch4 is the switch I'm investigating.
Switch4#sh int tru
Port Mode Encapsulation Status Native vlan
Gi1/2 on 802.1q trunking 1
Port Vlans allowed on trunk
Gi1/2 1-4094
Port Vlans allowed and active in management domain
Gi1/2 1-2,30,40,42,50,60,70,72,8
Port Vlans in spanning tree forwarding state and not pruned
Gi1/2 1-2,30,40,42,50,60,70,72,8
Switch4#sh int gi1/2
GigabitEthernet1/2 is up, line protocol is up (connected)
Hardware is Gigabit Ethernet, address is XXXX.dbd3.f0b2 (bia 30e4.dbd3.f0b2)
Confirming which port is trunked back to Switch1
=======
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
The mac address shows up when I search for it
Switch1#sh mac address-table | inc f0b2
Switch1#sh mac
The mac address doesn't show up suddenly
Switch1#sh mac address-table | inc Gi2/1/3
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
1 XXXX.480e.2751 DYNAMIC Gi2/1/3
40 XXXX.11a0.5372 DYNAMIC Gi2/1/3
70 XXXX.5f0e.a116 DYNAMIC Gi2/1/3
80 XXXX.b6da.d050 DYNAMIC Gi2/1/3
100 XXXX.dbd3.f0c1 DYNAMIC Gi2/1/3
The mac address shows up in the table now
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
The mac address shows up when I search for it again
Switch1#sh mac address-table | inc f0b2
Then it doesn't
Switch1#sh mac address-table | inc Gi2/1/3
1 XXXX.480e.2751 DYNAMIC Gi2/1/3
40 XXXX.11a0.5372 DYNAMIC Gi2/1/3
70 XXXX.5f0e.a116 DYNAMIC Gi2/1/3
80 XXXX.b6da.d050 DYNAMIC Gi2/1/3
100 XXXX.dbd3.f0c1 DYNAMIC Gi2/1/3
And it doesn't show up in the mac address table now
Switch1#sh mac address-table | inc f0b2
1 XXXX.dbd3.f0b2 DYNAMIC Gi2/1/3
Now it's back
Can anyone explain why this behavior is going on? I've checked on a few more trunk ports between my switches and I don't run into the "disappearing mac address" issue.
I would try to shutdown both trunk ports then turn then on again and let them re-negotiate the trunk. See if that clears up the issue.
Config t
Int g1/2
Shut
Config t
Int g2/1/3
Shut
Then "no shut" on both
Config t
Int g1/2
Shut
Config t
Int g2/1/3
Shut
Then "no shut" on both
ASKER
Don, to answer your questions in order:
1) Not much time between issuing the commands, less than a minute.
2) Those switches are connected by one fiber pair
3) There was another path from switch4 to switch1 until recently, I shut that interface off.
lruiz, I think in connection with the answer to Don's last question I should restart those interfaces.
1) Not much time between issuing the commands, less than a minute.
2) Those switches are connected by one fiber pair
3) There was another path from switch4 to switch1 until recently, I shut that interface off.
lruiz, I think in connection with the answer to Don's last question I should restart those interfaces.
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ASKER
Thanks for the thorough answer.
1) How much time between issuing the "show mac" commands?
2) Is Switch1, Gi2/1/3 connected to Switch4 Gi1/2?
3) Are you sure there is no other path from Switch1 to this host?