Cisco EtherChannels: Настройка и мониторинг канала агрегирования портов

EtherChannel Overview

Configuring EtherChannels Restrictions for EtherChannels, on page 1 Information About EtherChannels, on page 1 How to Configure EtherChannels, on page 13 Monitoring EtherChannel, Port Aggregation Protocol, and Link Aggregation Control Protocol Status, on page 30 Configuration Examples for EtherChannels, on page 31 Additional References for EtherChannels, on page 34 Feature History for EtherChannels, on page 34 Restrictions for EtherChannels The following are restrictions for EtherChannels: • All ports in an EtherChannel must be assigned to the same VLAN or they must be configured as trunk port. • The LACP 1:1 redundancy feature is supported on port channel interfaces only.

• On EtherChannel member port selection is software based in Layer 2 and Layer 3 multicast route. This means that all multicast traffic under a group will be routed via the same physical port of the EtherChannel. As a result, the distribution of multicast traffic load balance over etherchannels might not evenly spread across member ports. Information About EtherChannels The following sections provide information about EtherChannels and the various modes to configure EtherChannels. EtherChannel Overview EtherChannel provides fault-tolerant high-speed links between switches, routers, and servers.

You can use the EtherChannel to increase the bandwidth between the wiring closets and the data center, and you can deploy it anywhere in the network where bottlenecks are likely to occur. EtherChannel provides automatic recovery Configuring EtherChannels 1

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Channel Groups and Port-Channel Interfaces

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. An EtherChannel consists of individual Ethernet links bundled into a single logical link. Figure 1: Typical EtherChannel Configuration Each EtherChannel can consist of up to eight compatibly configured Ethernet ports. Channel Groups and Port-Channel Interfaces An EtherChannel comprises a channel group and a port-channel interface. The channel group binds physical ports to the port-channel interface.

Configuration changes applied to the port-channel interface apply to all the physical ports bound together in the channel group. Figure 2: Relationship Between Physical Ports, a Channel Group, and a Port-Channel Interface The channel-group command binds the physical port and the port-channel interface together. Each EtherChannel has a port-channel logical interface numbered from 1 to 128. This port-channel interface number corresponds to the one specified with the channel-group interface configuration command. Configuring EtherChannels Channel Groups and Port-Channel Interfaces Configuring EtherChannels 2

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Port Aggregation Protocol Modes

• With Layer 2 ports, use the channel-group interface configuration command to dynamically create the port-channel interface. You also can use the interface port-channel port-channel-number global configuration command to manually create the port-channel interface, but then you must use the channel-group channel-group-number command to bind the logical interface to a physical port. The channel-group-number can be the same as the port - channel-number, or you can use a new number. If you use a new number, the channel-group command dynamically creates a new port channel.

• With Layer 3 ports, you should manually create the logical interface by using the interface port-channel global configuration command followed by the no switchport interface configuration command. You then manually assign an interface to the EtherChannel by using the channel-group interface configuration command. • With Layer 3 ports, use the no switchport interface command to configure the interface as a Layer 3 interface, and then use the channel-group interface configuration command to dynamically create the port-channel interface.

Port Aggregation Protocol The Port Aggregation Protocol (PAgP) is a Cisco-proprietary protocol that can be run only on Cisco devices and on those devices that are licensed by vendors to support PAgP. PAgP facilitates the automatic creation of EtherChannels by exchanging PAgP packets between Ethernet ports. PAgP can be enabled on cross-stack EtherChannels. By using PAgP, the switch or switch stack learns the identity of partners capable of supporting PAgP and the capabilities of each port. It then dynamically groups similarly configured ports (on a single device in the stack) into a single logical link (channel or aggregate port).

Similarly configured ports are grouped based on hardware, administrative, and port parameter constraints. For example, PAgP groups the ports with the same speed, duplex mode, native VLAN, VLAN range, and trunking status and type. After grouping the links into an EtherChannel, PAgP adds the group to the spanning tree as a single device port. Port Aggregation Protocol Modes PAgP modes specify whether a port can send PAgP packets, which start PAgP negotiations, or only respond to PAgP packets received. Table 1: EtherChannel PAgP Modes Switch ports exchange PAgP packets only with partner ports that are configured in the auto or desirable modes.

Ports that are configured in the on mode do not exchange PAgP packets. Both the auto and desirable modes enable ports to negotiate with partner ports to form an EtherChannel based on criteria such as port speed. and for Layer 2 EtherChannels, based on trunk state and VLAN numbers. Configuring EtherChannels Port Aggregation Protocol Mode Description auto Places a port into a passive negotiating state, in which the port responds to PAgP packets it receives but does not start PAgP packet negotiation. This setting minimizes the transmission of PAgP packets. desirable Places a port into an active negotiating state, in which the port starts negotiations with other ports by sending PAgP packets.

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Port Aggregation Protocol Learn Method and Priority

Ports can form an EtherChannel when they are in different PAgP modes as long as the modes are compatible. For example: • A port in the desirable mode can form an EtherChannel with another port that is in the desirable or auto mode. • A port in the auto mode can form an EtherChannel with another port in the desirable mode. A port in the auto mode cannot form an EtherChannel with another port that is also in the auto mode because neither port starts PAgP negotiation. Silent Mode If your switch is connected to a partner that is PAgP-capable, you can configure the switch port for nonsilent operation by using the non-silent keyword.

If you do not specify non-silent with the auto or desirable mode, silent mode is assumed. Use the silent mode when the switch is connected to a device that is not PAgP-capable and seldom, if ever, sends packets. An example of a silent partner is a file server or a packet analyzer that is not generating traffic. In this case, running PAgP on a physical port that is connected to a silent partner prevents that switch port from ever becoming operational. However, the silent setting allows PAgP to operate, to attach the port to a channel group, and to use the port for transmission.

Port Aggregation Protocol Learn Method and Priority Network devices are classified as PAgP physical learners or aggregate-port learners. A device is a physical learner if it learns addresses by physical ports and directs transmissions based on that knowledge. A device is an aggregate-port learner if it learns addresses by aggregate (logical) ports. The learn method must be configured the same at both ends of the link. When a device and its partner are both aggregate-port learners, they learn the address on the logical port-channel. The device sends packets to the source by using any of the ports in the EtherChannel.

With aggregate-port learning, it is not important on which physical port the packet arrives. PAgP cannot automatically detect when the partner device is a physical learner and when the local device is an aggregate-port learner. Therefore, you must manually set the learning method on the local device to learn addresses by physical ports. You also must set the load-distribution method to source-based distribution, so that any given source MAC address is always sent on the same physical port. You also can configure a single port within the group for all transmissions and use other ports for hot-standby.

The unused ports in the group can be swapped into operation in just a few seconds if the selected single port loses hardware-signal detection. You can configure which port is always selected for packet transmission by changing its priority with the pagp port-priority interface configuration command. The higher the priority, the more likely that the port will be selected. Configuring EtherChannels Silent Mode Configuring EtherChannels 4

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