Catalyst 4500 Series Switch Software Configuration Guide, IOS XE 3.6.xE and IOS 15.2(2)Ex

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
• Manual EtherChannel Configuration
• PAgP EtherChannel Configuration
• IEEE 802.3ad LACP EtherChannel Configuration

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 26-1 lists the user-configurable EtherChannel modes.

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.

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
• Configuring Physical Interfaces as Layer 3 EtherChannels

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:

This example shows how to create port channel interface 1:

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

Configuring Physical Interfaces as Layer 3 EtherChannels

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

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

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:

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

This example shows how to display a one-line summary per channel group:

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:

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

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:

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

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

Configuring LACP Standalone or Independent Mode

This feature is particularly relevant when a port (A) in a Layer 2 LACP EtherChannel is connected to an unresponsive port (B) on the peer. When LACP standalone is disabled on the EtherChannel, all traffic arriving on A is blocked (the default behavior on a switch). In some scenarios, you might want to allow management traffic on such ports. You can do this by enabling LACP standalone (or independent) mode.

Note This port-channel standalone-disable command only applies to Layer 2 EtherChannels

Note LACP Standalone Disable is enabled by default.

To configure the LACP Standalone or Independent mode, perform this task:

This example shows how to configure the LACP Standalone mode:

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

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

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:

This example shows how to configure the LACP system priority:

This example shows how to verify the configuration:

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:

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:

This example shows how to verify the configuration:

Removing an Interface from an EtherChannel

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

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

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:

This example shows how to remove port channel 1:

Understanding VSS Client

This section describes these topics:

• Virtual Switch System
• Dual-Active Scenarios
• Dual-Active Detection Using Enhanced PAgP

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 26-1). 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 26-2). 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 26-1 Enhanced PAgP in VSS Normal Operation

Figure 26-2 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:

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

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:

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

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:

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