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Troubleshooting Spanning Tree Troubleshooting Spanning Tree
OmniSwitch Troubleshooting Guide September 2005 page 4-3
Use the show spantree ports command to determine if the port is in forwarding or blocking and are in the
correct VLAN. Remember that in any LAN with physical redundancy there must be at least one port in
blocking status. If it is known which ports are usually in blocking, those ports can be a good place to start
to verify they are still in blocking status.
-> show spantree ports
Vlan Port Oper Status Path Cost Role
-----+-----+------------+---------+-----
10 5/10 FORW 100 DESG
If ports that should be in blocking are now in forwarding, there are two likely causes. The first is that there
was a physical failure in a link that was previously in forwarding. The second is that the BPDUs from the
root are being dropped. If it appears that BPDUs are being dropped, troubleshoot this as if it were any
other packet being dropped.
Use the show interfaces command to look for errors incrementing on the port as well as to verify duplex
settings match on either side of the link.
-> show interfaces 5/10
Slot/Port 5/10 :
Operational Status : up,
Type : Fast Ethernet,
MAC address : 00:d0:95:7a:63:90,
BandWidth (Megabits) : 10, Duplex : Half,
Long Accept : Enable, Runt Accept : Disable,
Long Frame Size(Bytes) : 1553, Runt Size(Bytes) : 64
Input :
Bytes Received : 765702,
Lost Frames : 0,
Unicast Frames : 2317,
Broadcast Frames : 3855,
Multicast Frames : 480,
UnderSize Frames : 0,
OverSize Frames : 0,
Collision Frames : 0,
Error Frames : 0,
CRC Error Frames : 0,
Alignments Error : 0
Output :
Bytes transmitted : 566131,
Lost Frames : 0,
Unicast Frames : 2153,
Broadcast Frames : 8,
Multicast Frames : 5931,
UnderSize Frames : 0,
OverSize Frames : 0,
Collision Frames : 0,
Error Frames : 0