Alcatel Carrier Internetworking Solutions Omni Switch/Router - Manual (Page 1031)

Operational Problems
Page 35-7
To determine if this problem has occurred in your setup, you can use the vi command to
display information about a specific port. (See Chapter 19, “Managing Groups and Ports,” for
more information on the
vi command.) The syntax for this command is as follows:
vi <slot>/<interface>
The system will show the port in Blocking mode and not in Forwarding mode.
Probable Cause
You did not configure the network from the point furthest away from the point of connection.
Solution
To rectify the problem, you should always start configuration from the switch that is the
furthest away from the point of connection. In the figure on page 35-6, for example, you
would start the change from V2 in Switch X. By configuring this switch first, you would set it
up to see the two
VLANs in Switch Y, and use two Spanning Trees to looping.
Problems with IP Applications
You may have enabled routing on a VLAN , but have problems with PING and other IP applica-
tions.
Probable Cause
When routing is enabled on a VLAN , packets will not be forwarded unless the Spanning Tree
Status for the port being forwarded to has progressed from Listening to Learning to Forward-
ing.
You can determine if Spanning Tree Protocol has entered the Forwarding state for a port by
viewing port status with the
sts command. Refer to Chapter 17, “Configuring Bridging Param-
eters,” for information on Spanning Tree Status and the sts command.
Solution
Spanning Tree algorithms put the ports into the correct state. There may be propagation
delays when the Spanning Tree passes protocol information throughout a bridged network.
This is normal as bridge ports wait for new topology information and for the lifetime of
frames being forwarded using the old topology to expire. Immediate transitions from port
state to port state should not be expected.
If the port is in the blocking mode, then the Spanning Tree has detected a loop. Blocking is a
desired, preventive measure invoked by the Spanning Tree algorithm.
You should not attempt to alter the port state or remove the Spanning Tree. If you attempt to
move a port from non-participation to the forwarding state, you take the risk of introducing
data loops.
Once in the Forwarding state, PINGs and other IP applications should function properly.