Configuring EtherChannel and Link State Tracking

This chapter describes how to use the command-line interface (CLI) to configure EtherChannel on the Catalyst 4500 series switch Layer 2 or Layer 3 interfaces. It also provides guidelines, procedures, and configuration examples.

EtherChannel provides automatic recovery for the loss of a link by redistributing the load across the remaining links. If a link fails, EtherChannel redirects traffic from the failed link to the remaining links in the channel without intervention. This chapter also describes how to configure link-state tracking.

This chapter includes the following major sections:

Note The commands in the following sections can be used on all Ethernet interfaces on a Catalyst 4500 series switch, including the uplink ports on the supervisor engine.

Note For complete syntax and usage information for the switch commands used in this chapter, look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it is located in the larger Cisco IOS library. Refer to the Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

About EtherChannel

EtherChannel bundles up to eight individual Ethernet links into a single logical ink that provides an aggregate bandwidth of up to 800 Mbps (Fast EtherChannel), 8 Gbps (Gigabit EtherChannel), or 80 Gbps (10 Gigabit EtherChannel) between a Catalyst 4500 or 4500X series switch and another switch or host.

Note Because some linecards have a maximum bandwidth capacity toward the backplane, they can limit the aggregate bandwidth of an EtherChannel when all the EtherChannel members belong to the same linecard.

A Catalyst 4500 series switch supports a maximum of 64 EtherChannels. You can form an EtherChannel with up to eight compatibly configured Ethernet interfaces across modules in a Catalyst 4500 series switch. All interfaces in each EtherChannel must be the same speed and must be configured as either Layer 2 or Layer 3 interfaces.

Note The network device to which a Catalyst 4500 series switch is connected may impose its own limits on the number of interfaces in an EtherChannel.

If a segment within an EtherChannel fails, traffic previously carried over the failed link switches to the remaining segments within the EtherChannel. When the segment fails, an SNMP trap is sent, identifying the switch, the EtherChannel, and the failed link. Inbound broadcast and multicast packets on one segment in an EtherChannel are blocked from returning on any other segment of the EtherChannel.

Note The port channel link failure switchover for the Catalyst 4500 series switch was measured at 50 miliseconds, which provides SONET-like link failure switchover time.

These subsections describe how EtherChannel works:

Port Channel Interfaces

Each EtherChannel has a numbered port channel interface. A configuration applied to the port channel interface affects all physical interfaces assigned to that interface.

Note QoS does not propagate to members. The defaults, QoS cos = 0 and QoS dscp = 0, apply on the port channel. Input or output policies applied on individual interfaces are ignored.

After you configure an EtherChannel, the configuration that you apply to the port channel interface affects the EtherChannel; the configuration that you apply to the physical interfaces affects only the interface where you apply the configuration. To change the parameters of all ports in an EtherChannel, apply configuration commands to the port channel interface (such commands can be STP commands or commands to configure a Layer 2 EtherChannel as a trunk).

Configuring EtherChannels

These subsections describe how EtherChannels are configured:

EtherChannel Configuration Overview

You can configure EtherChannels manually or use the Port Aggregation Control Protocol (PAgP) or the Link Aggregation Control Protocol (LACP) (Cisco IOS Release 12.2(25)EWA and later), to form EtherChannels. The EtherChannel protocols allow ports with similar characteristics to form an EtherChannel through dynamic negotiation with connected network devices. PAgP is a Cisco-proprietary protocol and LACP is defined in IEEE 802.3ad.

PAgP and LACP do not interoperate. Ports configured to use PAgP cannot form EtherChannels with ports configured to use LACP and vice versa.

Table 22-1 lists the user-configurable EtherChannel modes.

 

Table 22-1 EtherChannel Modes

Mode
Description

on

Mode that forces the LAN port to channel unconditionally. In the on mode, a usable EtherChannel exists only when a LAN port group in the on mode is connected to another LAN port group in the on mode. Because ports configured in the on mode do not negotiate, there is no negotiation traffic between the ports.

auto

PAgP mode that places a LAN port into a passive negotiating state in which the port responds to PAgP packets it receives but does not initiate PAgP negotiation.

desirable

PAgP mode that places a LAN port into an active negotiating state in which the port initiates negotiations with other LAN ports by sending PAgP packets.

passive

LACP mode that places a port into a passive negotiating state in which the port responds to LACP packets it receives but does not initiate LACP negotiation.

active

LACP mode that places a port into an active negotiating state in which the port initiates negotiations with other ports by sending LACP packets.

Manual EtherChannel Configuration

Manually configured EtherChannel ports do not exchange EtherChannel protocol packets. A manually configured EtherChannel forms only when you configure all ports compatibly in the EtherChannel.

PAgP EtherChannel Configuration

PAgP supports the automatic creation of EtherChannels by exchanging PAgP packets between LAN ports. PAgP packets are exchanged only between ports in auto and desirable modes.

The protocol learns the capabilities of LAN port groups dynamically and informs the other LAN ports. Once PAgP identifies correctly matched Ethernet links, it facilitates grouping the links into an EtherChannel. The EtherChannel is then added to the spanning tree as a single bridge port.

Both the auto and desirable modes allow PAgP to negotiate between LAN ports to determine if they can form an EtherChannel, based on criteria such as port speed and trunking state. Layer 2 EtherChannels also use VLAN numbers.

LAN ports can form an EtherChannel when they are in different PAgP modes if the modes are compatible. For example:

  • A LAN port in desirable mode can form an EtherChannel successfully with another LAN port that is in desirable mode.
  • A LAN port in desirable mode can form an EtherChannel with another LAN port in auto mode.
  • A LAN port in auto mode cannot form an EtherChannel with another LAN port that is also in auto mode because neither port initiates negotiation.

IEEE 802.3ad LACP EtherChannel Configuration

Cisco IOS Release 12.2(25)EWA and later releases support IEEE 802.3ad LACP EtherChannels. LACP supports the automatic creation of EtherChannels by exchanging LACP packets between LAN ports. LACP packets are exchanged only between ports in passive and active modes.

The protocol learns the capabilities of LAN port groups dynamically and informs the other LAN ports. Once LACP identifies correctly matched Ethernet links, it facilitates grouping the links into an EtherChannel. The EtherChannel is then added to the spanning tree as a single bridge port.

Both the passive and active modes allow LACP to negotiate between LAN ports to determine if they can form an EtherChannel, based on criteria such as port speed and trunking state. Layer 2 EtherChannels also use VLAN numbers.

LAN ports can form an EtherChannel when they are in different LACP modes as long as the modes are compatible. For example:

  • A LAN port in active mode can form an EtherChannel successfully with another LAN port that is in active mode.
  • A LAN port in active mode can form an EtherChannel with another LAN port in passive mode.
  • A LAN port in passive mode cannot form an EtherChannel with another LAN port that is also in passive mode, because neither port initiates negotiation.

LACP uses the following parameters:

  • LACP system priority—You may configure an LACP system priority on each switch running LACP. The system priority can be configured automatically or through the CLI. See the “Configuring the LACP System Priority and System ID” section. LACP uses the system priority with the switch MAC address to form the system ID and also during negotiation with other systems.

Note The LACP system ID is the combination of the LACP system priority value and the MAC address of the switch.

  • LACP port priority—You must configure an LACP port priority on each port configured to use LACP. The port priority can be configured automatically or through the CLI. See the “Configuring Layer 2 EtherChannels” section. LACP uses the port priority with the port number to form the port identifier.
  • LACP administrative key—LACP automatically configures an administrative key value equal to the channel group identification number on each port configured to use LACP. The administrative key defines the ability of a port to aggregate with other ports. A port’s ability to aggregate with other ports is determined by these factors:

– Port physical characteristics, such as data rate, duplex capability, and point-to-point or shared medium

– Configuration restrictions that you establish

LACP tries to configure the maximum number of compatible ports in an EtherChannel up to the maximum allowed by the hardware (eight ports). If a port cannot be actively included in a channel, it is not included automatically if a channelled port fails.

Note Standby and “sub-channeling” are not supported in LACP and PAgP.

Load Balancing

EtherChannel can balance the traffic load across the links in the channel by reducing part of the binary pattern formed from the addresses or ports in the frame to a numerical value that selects one of the links in the channel. To balance the load, EtherChannel uses MAC addresses, IP addresses, or Layer 4 port numbers, and either the message source or message destination, or both.

Use the option that provides the greatest variety in your configuration. For example, if the traffic on a channel is going only to a single MAC address, using the destination MAC address always chooses the same link in the channel; using source addresses or IP addresses might result in better load balancing.

Note Load balancing can only be configured globally. As a result, all channels (manually configured, PagP, or LACP) use the same load-balancing method.

For additional information on load balancing, see the “Configuring EtherChannel Load Balancing” section.

EtherChannel Configuration Guidelines and Restrictions

If improperly configured, some EtherChannel interfaces are disabled automatically to avoid network loops and other problems. Follow these guidelines and restrictions to avoid configuration problems:

  • All Ethernet interfaces on all modules support EtherChannel (maximum of eight interfaces) with no requirement that interfaces be physically contiguous or on the same module.
  • Configure all interfaces in an EtherChannel to operate at the same speed and duplex mode.
  • Enable all interfaces in an EtherChannel. Disabling an interface in an EtherChannel is treated as a link failure, and its traffic is transferred to one of the remaining interfaces in the EtherChannel.
  • An EtherChannel does not form if one of the interfaces is a Switched Port Analyzer (SPAN) destination port.
  • For Layer 3 EtherChannels:

– Assign Layer 3 addresses to the port channel logical interface, not to the physical interfaces in the channel.

  • For Layer 2 EtherChannels:

– Assign all interfaces in the EtherChannel to the same VLAN, or configure them as trunks.

– If you configure an EtherChannel from trunk interfaces, verify that the trunking mode and the native VLAN is the same on all the trunks. Interfaces in an EtherChannel with different trunk modes or different native VLANs can have unexpected results.

– An EtherChannel supports the same allowed range of VLANs on all the interfaces in a trunking Layer 2 EtherChannel. If the allowed ranges differ for selected interface differ, they do not form an EtherChannel.

– Interfaces with different Spanning Tree Protocol (STP) port path costs can form an EtherChannel as long they are otherwise compatibly configured. Setting different STP port path costs does not make interfaces incompatible for the formation of an EtherChannel.

  • After you configure an EtherChannel, any configuration that you apply to the port channel interface affects the EtherChannel; any configuration that you apply to the physical interfaces affects only the interface you configure.

Storm Control is an exception to this rule. For example, you cannot configure Storm Control on some of the members of an EtherChannel; Storm Control must be configured on all or none of the ports. If you configure Storm Control on only some of the ports, those ports are dropped from the EtherChannel interface (put in suspended state). You should configure Storm Control at the port channel interface level, and not at the physical interface level.

  • A physical interface with port security enabled can join a Layer 2 EtherChannel only if port security is also enabled on the EtherChannel; otherwise the command is rejected by the CLI.
  • You cannot configure a 802.1X port in an EtherChannel.

Configuring EtherChannel

These sections describe how to configure EtherChannel:

Note Ensure that the interfaces are configured correctly. See the “EtherChannel Configuration Guidelines and Restrictions” section.

Configuring Layer 3 EtherChannels

To configure Layer 3 EtherChannels, create the port channel logical interface and then put the Ethernet interfaces into the port channel.

These sections describe Layer 3 EtherChannel configuration:

Creating Port Channel Logical Interfaces

Note To move an IP address from a physical interface to an EtherChannel, you must delete the IP address from the physical interface before configuring it on the port channel interface.

To create a port channel interface for a Layer 3 EtherChannel, perform this task:

 

Command
Purpose

Step 1
Switch(config)# interface port-channel port_channel_number

Creates the port channel interface. The value for port_channel _number can range from 1 to 64.

Step 2
Switch(config-if)# ip address ip_address mask

Assigns an IP address and subnet mask to the EtherChannel.

Step 3
Switch(config-if)# end

Exits configuration mode.

Step 4
Switch# show running-config interface port-channel port_channel_number

Verifies the configuration.

This example shows how to create port channel interface 1:

Switch# configure terminal
Switch(config)# interface port-channel 1
Switch(config-if)# ip address 172.32.52.10 255.255.255.0
Switch(config-if)# end
 

This example shows how to verify the configuration of port channel interface 1:

Switch# show running-config interface port-channel 1
Building configuration...
 
Current configuration:
!
interface Port-channel1
ip address 172.32.52.10 255.255.255.0
no ip directed-broadcast
end
 
Switch#

Configuring Physical Interfaces as Layer 3 EtherChannels

To configure physical interfaces as Layer 3 EtherChannels, perform this task for each interface:

 

Command
Purpose

Step 1
Switch(config)# interface { fastethernet | gigabitethernet | tengigabitethernet } slot / port

Selects a physical interface to configure.

Step 2
Switch(config-if)# no switchport

Makes this a Layer 3 routed port.

Step 3
Switch(config-if)# no ip address

Ensures that no IP address is assigned to the physical interface.

Step 4
Switch(config-if)# channel-group port_channel_number mode {active | on | auto | passive | desirable }

Configures the interface in a port channel and specifies the PAgP or LACP mode.

If you use PAgP, enter the keywords auto or desirable.

If you use LACP, enter the keywords active or passive.

Step 5
Switch(config-if)# end

Exits configuration mode.

Step 6
Switch# show running-config interface port-channel port_channel_number
 
Switch# show running-config interface { fastethernet | gigabitethernet | tengigabitethernet } slot / port
 
Switch# show interfaces { fastethernet | gigabitethernet | tengigabitethernet } slot / port etherchannel
 
Switch# show etherchannel 1 port-channel

Verifies the configuration.

This example shows how to configure Fast Ethernet interfaces 5/4 and 5/5 into port channel 1 with PAgP mode desirable :

Switch# configure terminal
Switch(config)# interface range fastethernet 5/4 - 5 (Note: Space is mandatory.)
Switch(config-if)# no switchport
Switch(config-if)# no ip address
Switch(config-if)# channel-group 1 mode desirable
Switch(config-if)# end

Note See the “Configuring a Range of Interfaces” section for information about the range keyword.

The following two examples show how to verify the configuration of Fast Ethernet interface 5/4:

Switch# show running-config interface fastethernet 5/4
Building configuration...
 
Current configuration:
!
interface FastEthernet5/4
no ip address
no switchport
no ip directed-broadcast
channel-group 1 mode desirable
end
 
Switch# show interfaces fastethernet 5/4 etherchannel
Port state = EC-Enbld Up In-Bndl Usr-Config
Channel group = 1 Mode = Desirable Gcchange = 0
Port-channel = Po1 GC = 0x00010001 Pseudo-port-channel = Po1
Port indx = 0 Load = 0x55
 
Flags: S - Device is sending Slow hello. C - Device is in Consistent state.
A - Device is in Auto mode. P - Device learns on physical port.
Timers: H - Hello timer is running. Q - Quit timer is running.
S - Switching timer is running. I - Interface timer is running.
 
Local information:
Hello Partner PAgP Learning Group
Port Flags State Timers Interval Count Priority Method Ifindex
Fa5/4 SC U6/S7 30s 1 128 Any 55
 
Partner's information:
 
Partner Partner Partner Partner Group
Port Name Device ID Port Age Flags Cap.
Fa5/4 JAB031301 0050.0f10.230c 2/45 1s SAC 2D
 
Age of the port in the current state: 00h:54m:52s
 
Switch#
 

This example shows how to verify the configuration of port channel interface 1 after the interfaces have been configured:

Switch# show etherchannel 1 port-channel
 
Channel-group listing:
----------------------
Group: 1
------------
 
Port-channels in the group:
----------------------
Port-channel: Po1
------------
 
Age of the Port-channel = 01h:56m:20s
Logical slot/port = 10/1 Number of ports = 2
GC = 0x00010001 HotStandBy port = null
Port state = Port-channel L3-Ag Ag-Inuse
 
Ports in the Port-channel:
 
Index Load Port
-------------------
1 00 Fa5/6
0 00 Fa5/7
 
Time since last port bundled: 00h:23m:33s Fa5/6
 
Switch#

Configuring Layer 2 EtherChannels

To configure Layer 2 EtherChannels, configure the Ethernet interfaces with the channel-group command. This operation creates the port channel logical interface.

Note Cisco IOS software creates port channel interfaces for Layer 2 EtherChannels when you configure Layer 2 Ethernet interfaces with the channel-group command.

To configure Layer 2 Ethernet interfaces as Layer 2 EtherChannels, perform this task for each interface:

 

Command
Purpose

Step 1
Switch(config)# interface { fastethernet | gigabitethernet | tengigabitethernet } slot / port

Selects a physical interface to configure.

Step 2
Switch(config-if)# channel-group port_channel_number mode {active | on | auto | passive | desirable }

Configures the interface in a port channel and specifies the PAgP or LACP mode.

If you use PAgP, enter the keywords auto or desirable.

If you use LACP, enter the keywords active or passive.

Step 3
Switch(config-if)# end

Exits configuration mode.

Step 4
Switch# show running-config interface { fastethernet | gigabitethernet } slot / port
 
Switch# show interface { fastethernet | gigabitethernet | tengigabitethernet } slot / port etherchannel

Verifies the configuration.

This example shows how to configure Fast Ethernet interfaces 5/6 and 5/7 into port channel 2 with PAgP mode desirable :

Switch# configure terminal
Switch(config)# interface range fastethernet 5/6 - 7 (Note: Space is mandatory.)
Switch(config-if-range)# channel-group 2 mode desirable
Switch(config-if-range)# end
Switch# end

Note See the “Configuring a Range of Interfaces” section for information about the range keyword.

This example shows how to verify the configuration of port channel interface 2:

Switch# show running-config interface port-channel 2
Building configuration...
 
Current configuration:
!
interface Port-channel2
switchport access vlan 10
switchport mode access
end
 
Switch#
 

The following two examples show how to verify the configuration of Fast Ethernet interface 5/6:

Switch# show running-config interface fastethernet 5/6
Building configuration...
 
Current configuration:
!
interface FastEthernet5/6
switchport access vlan 10
switchport mode access
channel-group 2 mode desirable
end
 
Switch# show interfaces fastethernet 5/6 etherchannel
Port state = EC-Enbld Up In-Bndl Usr-Config
Channel group = 1 Mode = Desirable Gcchange = 0
Port-channel = Po1 GC = 0x00010001
Port indx = 0 Load = 0x55
 
Flags: S - Device is sending Slow hello. C - Device is in Consistent state.
A - Device is in Auto mode. P - Device learns on physical port.
d - PAgP is down.
Timers: H - Hello timer is running. Q - Quit timer is running.
S - Switching timer is running. I - Interface timer is running.
Local information:
Hello Partner PAgP Learning Group
Port Flags State Timers Interval Count Priority Method Ifindex
Fa5/6 SC U6/S7 30s 1 128 Any 56
 
Partner's information:
 
Partner Partner Partner Partner Group
Port Name Device ID Port Age Flags Cap.
Fa5/6 JAB031301 0050.0f10.230c 2/47 18s SAC 2F
 
Age of the port in the current state: 00h:10m:57s
 

This example shows how to verify the configuration of port channel interface 2 after the interfaces have been configured:

Switch# show etherchannel 2 port-channel
Port-channels in the group:
----------------------
 
Port-channel: Po2
------------
 
Age of the Port-channel = 00h:23m:33s
Logical slot/port = 10/2 Number of ports in agport = 2
GC = 0x00020001 HotStandBy port = null
Port state = Port-channel Ag-Inuse
 
Ports in the Port-channel:
 
Index Load Port
-------------------
1 00 Fa5/6
0 00 Fa5/7
 
Time since last port bundled: 00h:23m:33s Fa5/6
 
Switch#

Configuring the LACP System Priority and System ID

The LACP system ID is the LACP system priority value combined with the MAC address of the switch.

To configure the LACP system priority and system ID, perform this task:

 

Command
Purpose

Step 1
Switch(config)# lacp system-priority priority_value

(Optional for LACP) Sets the LACP system priority and system ID.

Valid values are 1 through 65535. Higher numbers have lower priority. The default is 32768.
Switch(config)# no system port-priority

Reverts to the default.

Step 2
Switch(config)# end

Exits configuration mode.

Step 3
Switch# show lacp sys-id

Verifies the configuration.

This example shows how to configure the LACP system priority:

Switch# configure terminal
Switch(config)# lacp system-priority 23456
Switch(config)# end
Switch# show module
 
Mod Ports Card Type Model Serial No.
----+-----+--------------------------------------+-----------------+-----------
1 2 1000BaseX (GBIC) Supervisor(active) WS-X4014 JAB063808YZ
2 48 10/100BaseTX (RJ45) WS-X4148-RJ JAB0447072W
3 48 10/100BaseTX (RJ45)V WS-X4148-RJ45V JAE061704J6
4 48 10/100BaseTX (RJ45)V WS-X4148-RJ45V JAE061704ML
 
M MAC addresses Hw Fw Sw Status
--+--------------------------------+---+------------+----------------+---------
1 0005.9a39.7a80 to 0005.9a39.7a81 2.1 12.1(12r)EW 12.1(13)EW(0.26) Ok
2 0002.fd80.f530 to 0002.fd80.f55f 0.1 Ok
3 0009.7c45.67c0 to 0009.7c45.67ef 1.6 Ok
4 0009.7c45.4a80 to 0009.7c45.4aaf 1.6 Ok
 

This example shows how to verify the configuration:

Switch# show lacp sys-id
23456,0050.3e8d.6400
Switch#
 

The system priority is displayed first, followed by the MAC address of the switch.

Configuring EtherChannel Load Balancing

Note Load balancing can only be configured globally. As a result, all channels (manually configured, PagP, or LACP) use the same load-balancing method.

To configure EtherChannel load balancing, perform this task:

 

Command
Purpose

Step 1
Switch(config)# [ no ] port-channel load-balance { src-mac | dst-mac | src-dst-mac | src-ip | dst-ip | src-dst-ip | src-port | dst-port | src-dst-port }

Configures EtherChannel load balancing.

Use the no keyword to return EtherChannel load balancing to the default configuration.

Step 2
Switch(config)# end

Exits configuration mode.

Step 3
Switch# show etherchannel load-balance

Verifies the configuration.

The load-balancing keywords indicate these values:

  • src-mac —Source MAC addresses
  • dst-mac —Destination MAC addresses
  • src-dst-mac —Source and destination MAC addresses
  • src-ip —Source IP addresses
  • dst-ip —Destination IP addresses
  • src-dst-ip —Source and destination IP addresses (Default)
  • src-port —Source Layer 4 port
  • dst-port —Destination Layer 4 port
  • src-dst-port —Source and destination Layer 4 port

This example shows how to configure EtherChannel to use source and destination IP addresses:

Switch# configure terminal
Switch(config)# port-channel load-balance src-dst-ip
Switch(config)# end
Switch#
 

This example shows how to verify the configuration:

Switch# show etherchannel load-balance
EtherChannel Load-Balancing Configuration:
src-dst-ip
 
EtherChannel Load-Balancing Addresses Used Per-Protocol:
Non-IP: Source XOR Destination MAC address
IPv4: Source XOR Destination IP address
IPv6: Source XOR Destination IP address
Switch#

Removing an Interface from an EtherChannel

To remove an Ethernet interface from an EtherChannel, perform this task:

 

Command
Purpose

Step 1
Switch(config)# interface { fastethernet | gigabitethernet | tengigabitethernet } slot / port

Selects a physical interface to configure.

Step 2
Switch(config-if)# no channel-group

Removes the interface from the port channel interface.

Step 3
Switch(config-if)# end

Exits configuration mode.

Step 4
Switch# show running-config interface { fastethernet | gigabitethernet | tengigabitethernet } slot / port
Switch# show interface { fastethernet | gigabitethernet | tengigabitethernet } slot / port etherchannel

Verifies the configuration.

This example shows how to remove Fast Ethernet interfaces 5/4 and 5/5 from port channel 1:

Switch# configure terminal
Switch(config)# interface range fastethernet 5/4 - 5 (Note: Space is mandatory.)
Switch(config-if)# no channel-group 1
Switch(config-if)# end

Removing an EtherChannel

If you remove an EtherChannel, the member ports are shut down and removed from the channel group.

Note If you want to change an EtherChannel from Layer 2 to Layer 3, or Layer 3 to Layer 2, you must remove the EtherChannel and recreate it in the desired configuration.

To remove an EtherChannel, perform this task:

 

Command
Purpose

Step 1
Switch(config)# no interface port-channel port_channel_number

Removes the port channel interface.

Step 2
Switch(config)# end

Exits configuration mode.

Step 3
Switch# show etherchannel summary

Verifies the configuration.

This example shows how to remove port channel 1:

Switch# configure terminal
Switch(config)# no interface port-channel 1
Switch(config)# end

Displaying EtherChannel to a Virtual Switch System

Catalyst 4500 series switches support enhanced PAgP. If a Catalyst 4500 series switch is connected to a Catalyst 6500 series Virtual Switch System (VSS) by using a PAgP EtherChannel, the Catalyst 4500 series switch automatically serve as a VSS client, using enhanced PAgP on this EtherChannel for dual-active detection. This VSS client feature has no impact on the performance of Catalyst 4500 series switch and does not require any user configuration.

This section includes these topics:

Understanding VSS Client

This section describes these topics:

Virtual Switch System

The Cisco Catalyst 6500 Series VSS 1440 allows for the combination of two Cisco Catalyst 6500 Series switches into a single, logical network entity from the network control-plane and management perspectives. Within the Cisco VSS, one chassis is designated as the active virtual switch, acting as the single management point of the entire system, and the other is designated as the standby virtual switch. There two chassis are bound together by a special link, called Virtual Switch Link (VSL), which carries the internal signaling and control information between them.

Dual-Active Scenarios

One of the failure scenarios in a VSS is called dual-active, which occurs when the VSL fails completely. Neither virtual switch knows of the other's status. From the perspective of the active virtual switch, the standby chassis is lost. The standby virtual switch also views the active chassis as failed and transitions to active state by using an SSO switchover. Two active virtual switches exist in the network with identical configurations, causing duplicate IP addresses and bridge identifiers. This scenario has adverse effects on the network topology and traffic if it persists.

Dual-Active Detection Using Enhanced PAgP

One method for detecting a dual-active scenario is based on enhanced PAgP (PAgP+). Specifically, the VSS sends regularly scheduled PAgP messages with Type-Length-Values (TLVs) containing the ID of the current active virtual switch ( Figure 22-1). When the VSL fails completely, the standby virtual switch immediately sends asynchronous PAgP messages with TLVs containing its own ID on all port channels enabled for enhanced PAgP dual-active detection (Figure 22-2). The remote switch
(the VSS client) connected to both VSS components by using EtherChannel links, compares every received active ID with its stored active ID. If they match, the remote switch sends TLVs containing its stored active ID back to the VSS in its regularly scheduled PAgP messages. If they do not match, the remote switch stores the new active ID and immediately transmits asynchronous PAgP messages with TLVs containing the new active ID. Upon receiving the new active ID from the remote switch, the original active virtual switch detects the dual-active scenario and takes appropriate actions.

Figure 22-1 Enhanced PAgP in VSS Normal Operation

 

Figure 22-2 Enhanced PAgP in VSS Dual-active Scenario

 

As a remote switch, the Catalyst 4500 series switch supports stateful VSS client. In particular, the ID of the current active virtual switch is synchronized from the active supervisor engine to the redundant supervisor engine of the Catalyst 4500 series switch. This ensures that dual-active detection is not disrupted even when the active supervisor engine switches over to the redundant supervisor engine.

Displaying EtherChannel Links to VSS

To display the dual-active detection capability of a configured PAgP port channel, enter the
show pagp port_channel_number dual-active command.

The command provides the following information:

  • A switch uses enhanced PAgP for dual-active detection.

You should always see Yes after PAgP dual-active diction enabled on a Catalyst 4500 switch.

  • The configured PAgP EtherChannel is connected to a Catalyst 6500 switch VSS.

You see N/A below Partner Version if this EtherChannel is not connected to a VSS. Otherwise, you see the version of enhanced PAgP dual-active detection implemented in the VSS.

  • This switch is capable of detecting dual-active scenarios in the connected VSS.

You see Yes below Dual-Active Detect Capable if and only if the configured EtherChannel is connected to a Catalyst 6500 series VSS that uses the same version of enhanced PAgP dual-active detection.

Note You can also see the name of the neighboring switch (Partner Name) and the ports to which this EtherChannel is connected (Partner Port).

If a Catalyst 4500 switch is connected to a Catalyst 6500 series VSS with the same version of enhanced PAgP dual-active detection, the switch can detect a dual-active scenario:

Switch# show pagp 1 dual-active
PAgP dual-active detection enabled: Yes
PAgP dual-active version: 1.1
 
Channel group 1
Dual-Active Partner Partner Partner
Port Detect Capable Name Port Version
Gi6/5 Yes VSS Gi1/8/1 1.1
Gi6/6 Yes VSS Gi2/8/1 1.1
 

If a Catalyst 4500 switch is not connected to a Catalyst 6500 series VSS, the switch cannot detect a dual-active scenario:

Switch# show pagp 1 dual-active
PAgP dual-active detection enabled: Yes
PAgP dual-active version: 1.1
 
Channel group 1
Dual-Active Partner Partner Partner
Port Detect Capable Name Port Version
Gi6/5 No Switch Fa6/5 N/A
Gi6/6 No Switch Fa6/6 N/A

Understanding Link-State Tracking

Link-state tracking, also known as trunk failover, is a feature that binds the link state of multiple interfaces. For example, link-state tracking provides redundancy in the network when used with server NIC adapter teaming. When server network adapters are configured in a primary or secondary relationship known as teaming, if the link is lost on the primary interface, connectivity is transparently changed to the secondary interface.

Figure 22-3 shows a network configured with link-state tracking. To enable link-state tracking, create a link-state group, and specify the interfaces that are assigned to the link-state group. An interface can be an aggregation of ports (an EtherChannel), a single physical port in access or trunk mode, or a routed port. In a link-state group, these interfaces are bundled together. The downstream interfaces are bound to the upstream interfaces. Interfaces connected to servers are referred to as downstream interfaces, and interfaces connected to distribution switches and network devices are referred to as upstream interfaces.

The configuration in Figure 22-3 ensures that the network traffic flow is balanced as follows:

  • For links to switches and other network devices

– Server 1 and server 2 use switch A for primary links and switch B for secondary links.

– Server 3 and server 4 use switch B for primary links and switch A for secondary links.

  • Link-state group 1 on switch A

– Switch A provides primary links to server 1 and server 2 through link-state group 1. Port 1 is connected to server 1, and port 2 is connected to server 2. Port 1 and port 2 are the downstream interfaces in link-state group 1.

– Port 5 and port 6 are connected to distribution switch 1 through link-state group 1. Port 5 and port 6 are the upstream interfaces in link-state group 1.

  • Link-state group 2 on switch A

– Switch A provides secondary links to server 3 and server 4 through link-state group 2. Port 3 is connected to server 3, and port 4 is connected to server 4. Port 3 and port 4 are the downstream interfaces in link-state group 2.

– Port 7 and port 8 are connected to distribution switch 2 through link-state group 2. Port 7 and port 8 are the upstream interfaces in link-state group 2.

  • Link-state group 2 on switch B

– Switch B provides primary links to server 3 and server 4 through link-state group 2. Port 3 is connected to server 3, and port 4 is connected to server 4. Port 3 and port 4 are the downstream interfaces in link-state group 2.

– Port 5 and port 6 are connected to distribution switch 2 through link-state group 2. Port 5 and port 6 are the upstream interfaces in link-state group 2.

  • Link-state group 1 on switch B

– Switch B provides secondary links to server 1 and server 2 through link-state group 1. Port 1 is connected to server 1, and port 2 is connected to server 2. Port 1 and port 2 are the downstream interfaces in link-state group 1.

– Port 7 and port 8 are connected to distribution switch 1 through link-state group 1. Port 7 and port 8 are the upstream interfaces in link-state group 1.

In a link-state group, the upstream ports can become unavailable or lose connectivity because the distribution switch or router fails, the cables are disconnected, or the link is lost. These are the interactions between the downstream and upstream interfaces when link-state tracking is enabled:

  • If any of the upstream interfaces are in the link-up state, the downstream interfaces can change to or remain in the link-up state.
  • If all of the upstream interfaces become unavailable, link-state tracking automatically puts the downstream interfaces in the error-disabled state. Connectivity to and from the servers is automatically changed from the primary server interface to the secondary server interface.

As an example of a connectivity change from link-state group 1 to link-state group 2 on switch A, see Figure 22-3. If the upstream link for port 6 is lost, the link states of downstream ports 1 and 2 do not change. However, if the link for upstream port 5 is also lost, the link state of the downstream ports changes to the link-down state. Connectivity to server 1 and server 2 is then changed from link-state group1 to link-state group 2. The downstream ports 3 and 4 do not change state because they are in link-group 2.

  • If the link-state group is configured, link-state tracking is disabled, and the upstream interfaces lose connectivity, the link states of the downstream interfaces remain unchanged. The server does not recognize that upstream connectivity has been lost and does not failover to the secondary interface.

You can recover a downstream interface link-down condition by removing the failed downstream port from the link-state group. To recover multiple downstream interfaces, disable the link-state group.

Figure 22-3 Typical Link-State Tracking Configuration

 

Configuring Link-State Tracking

These sections describe how to configure link-state tracking ports:

Default Link-State Tracking Configuration

No link-state groups are defined, and link-state tracking is not enabled for any group.

Link-State Tracking Configuration Guidelines

Follow these guidelines to avoid configuration problems:

  • An interface that is defined as an upstream interface cannot also be defined as a downstream interface in the same or different link-state group. The reverse is also true.
  • We recommend that you add the upstream interfaces to the link state group before adding the downstream interfaces. it is because when a downstream interface is added to a link state group without an upstream interface, the downstream interface is put in error-disabled state until an upstream interfaces is added to the group.
  • An interface cannot be a member of more than one link-state group.
  • You can configure up to ten link-state groups per switch.
  • If a SPAN destination port is configured as a downstream interface, it is error disabled when all upstream interfaces in its group are down. When an upstream interface is configured as a SPAN destination port, it is considered as a link down event on the interface.

Configuring Link-State Tracking

To configure a link-state group and to assign an interface to a group, perform this task beginning in privileged EXEC mode:

 

Command
Purpose

Step 1
Switch# configure terminal

Enters global configuration mode.

Step 2
Switch(config)# link state track number

Creates a link-state group, and enable link-state tracking. The group number can be 1 to 10; the default is 1.

Step 3
Switch(config)# interface interface-id

Specifies a physical interface or range of interfaces to configure, and enters interface configuration mode.

Valid interfaces include switch ports in access or trunk mode (IEEE 802.1q), routed ports, or multiple ports bundled into an EtherChannel interface (static or LACP), also in trunk mode.

Step 4
Switch(config-if)# link state group number { upstream | downstream }

Specifies a link-state group, and configure the interface as either an upstream or downstream interface in the group.The group number can be 1 to 10; the default is 1.

Step 5
Switch(config-if)# end

Returns to privileged EXEC mode.

Step 6
Switch# show running-config

Verifies your entries.

Step 7
Switch# copy running-config startup-config

(Optional) Saves your entries in the configuration file.

This example shows how to create a link-state group and configure the interfaces:

Switch# configure terminal
Switch(config)# link state track 1
Switch(config)# interface gigabitethernet3/1
Switch(config-if)# link state group 1 upstream
Switch(config-if)# interface gigabitethernet3/3
Switch(config-if)# link state group 1 upstream
Switch(config-if)# interface gigabitethernet3/5
Switch(config-if)# link state group 1 downstream
Switch(config-if)# interface gigabitethernet3/7
Switch(config-if)# link state group 1 downstream
Switch(config-if)# end
 

To disable a link-state group, use the no link state track number global configuration command.

Displaying Link-State Tracking Status

To display the link-state group information, enter the show link state group command. Enter this command without keywords to display information about all link-state groups.

Enter the group number to display information specific to the group. Enter the detail keyword to display detailed information about the group.

it is an example of output from the show link state group 1 command:

Switch> show link state group 1
Link State Group: 1 Status: Enabled, Down
 

it is an example of output from the show link state group detail command:

Switch> show link state group detail
(Up):Interface up (Dwn):Interface Down (Dis):Interface disabled
Link State Group: 1 Status: Enabled, Down
Upstream Interfaces : Gi3/5(Dwn) Gi3/6(Dwn)
Downstream Interfaces : Gi3/1(Dis) Gi3/2(Dis) Gi3/3(Dis) Gi3/4(Dis)
Link State Group: 2 Status: Enabled, Down
Upstream Interfaces : Gi3/15(Dwn) Gi3/16(Dwn) Gi3/17(Dwn)
Downstream Interfaces : Gi3/11(Dis) Gi3/12(Dis) Gi3/13(Dis) Gi3/14(Dis)
(Up):Interface up (Dwn):Interface Down (Dis):Interface disabled