Cisco Catalyst 3750-X User Manual

22-10
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
OL-21521-01
Chapter 22 Configuring Optional Spanning-Tree Features
Understanding Optional Spanning-Tree Features
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 “EtherChannel Configuration G
uidelines” section on page 40-12.
If the switch detects a misconfigur
ation on the other device, EtherChannel guard places the switch
interfaces in the error-disabled state, and displays an error message.
You can enable this feature by using the spanni
ng-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 Figure 22-9. You can avoid this situation by enabling root guard on SP
switch interfaces that connect to switches in your custo
mer’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 sele
cts a new root switch. The customer’s switch does not become the root
switch and is not in the path to the root.
If the switch is operating in multiple spanning-tree (MST) mode, root guard forces the interface to be a
de
signated port. If a boundary port is blocked in an internal spanning-tree (IST) instance because of root
guard, the interface also is blocked in all MST instances. A boundary port is an interface that connects
to a LAN, the designated switch of which is either an IEEE 802.1D switch or a switch with a different
MST region configuration.
Root guard enabled on an interface applies to all the
VLANs to which the interface belongs. VLANs can
be grouped and mapped to an MST instance.
You can enable this feature by using the spanni
ng-tree guard root interface configuration command.
Caution Misuse of the root-guard feature can cause a loss of connectivity.

Cisco Catalyst 3750-X Specifications

General

Brand	Cisco
Model	Catalyst 3750-X
Category	Switch
Language	English