3Com 4007, Implementation Manual, Page: 293 / 684

Ignore STP Mode 293
Ignore STP Mode
When you use allClosed VLAN mode on a Multilayer Switching Module in
your system, you can enable the module to ignore the Spanning Tree
Protocol (STP) mode on a per-VLAN basis; that is, ignore STP blocked
ports. (When STP detects multiple paths to a destination, it blocks all but
one of the paths.)
If you have configured router port IP interfaces on your Multilayer
Switching Modules (which causes the module to generate router port
VLANs owned by the router IP interfaces), ignore STP mode is
automatically enabled and you cannot disable it.
Important
Considerations
■
Ignore STP mode is disabled by default for static VLANs.
■
You can use this mode only when the Multilayer Switching Module is
in allClosed mode.
■
Ignore STP mode is useful when you have redundant router
connections between modules that have STP enabled. In this situation,
if you want to create multiple VLANs and use one VLAN for routing,
you can configure your module to ignore the STP blocking mode for
that VLAN. This setting avoids disruptions to routing connectivity
based on the STP state.
■
To disable STP blocking on a per-port basis with allOpen or allClosed
VLANs, use the bridging option (
bridge port stpState
on the
Administration Console). See the Chapter 9 for bridging information.
Ignore STP mode affects bridging as well as routing. If you have STP
enabled on the system and you have redundant bridged paths between
systems with different VLANs, STP blocks one of the paths unless you
enable Ignore STP mode.
Example: Ignore STP
Mode
Figure 22 shows two paths available through the default VLAN and IP
VLAN2 if end station A wants to communicate with end station B. STP
blocks the routed as well as bridged traffic for the one path through IP
VLAN2 unless you enable Ignore STP Mode for IP VLAN2 (because the
backplane ports have higher priority). With the blocking removed for IP
routed traffic, the best path is used. (In this configuration, the switch
fabric module resides in slot 7 but is logically represented above the other
modules.)