Understanding Etherchannel Guard - Cisco Catalyst 3550 series Software Configuration Manual
Multilayer switch
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Also See for Catalyst 3550 series:
- Reference manual (58 pages) ,
- Datasheet (21 pages) ,
- Manual (19 pages)
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Understanding Optional Spanning-Tree Features
Figure 18-9 Adding a Switch in a Shared-Medium Topology
Switch C
Understanding EtherChannel Guard
You can use EtherChannel guard to detect an EtherChannel misconfiguration between the switch and a
connected device. A misconfiguration can occur if the switch interfaces are configured in an
EtherChannel, but the interfaces on the other device are not. A misconfiguration can also occur if the
channel parameters are not the same at both ends of the EtherChannel. For EtherChannel configuration
guidelines, see the
If the switch detects a misconfiguration on the other device, EtherChannel guard places the switch
interfaces in the error-disabled state, and this error message appears:
PM-4-ERR_DISABLE: Channel-misconfig error detected on [chars], putting [chars] in
err-disable state.
If your switch is running PVST+, rapid PVST+, or MSTP, you can enable this feature by using the
spanning-tree etherchannel guard misconfig global configuration command.
Understanding Root Guard
The Layer 2 network of a service provider (SP) can include many connections to switches that are not
owned by the SP. In such a topology, the spanning tree can reconfigure itself and select a customer switch
as the root switch, as shown in
switch interfaces that connect to switches in your customer's network. If spanning-tree calculations
cause an interface in the customer network to be selected as the root port, root guard then places the
interface in the root-inconsistent (blocked) state to prevent the customer's switch from becoming the root
switch or being in the path to the root.
If a switch outside the SP network becomes the root switch, the interface is blocked (root-inconsistent
state), and spanning tree selects a new root switch. The customer's switch does not become the root
switch and is not in the path to the root.
Catalyst 3550 Multilayer Switch Software Configuration Guide
18-12
Switch A
(Root)
Blocked port
Added switch
"EtherChannel Configuration Guidelines" section on page
Figure
18-10. You can avoid this situation by enabling root guard on SP
Chapter 18
Configuring Optional Spanning-Tree Features
Switch B
(Designated bridge)
30-8.
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