A Detailed Introduction of the Basis of Network Switching – Etherchannel

This article introduces the basis of network switching in detail – Etherchannel, a port aggregation technology.

No equipment can guarantee the absolute stability of operation, even the best products cannot guarantee 24 × 7 continuous working. In addition to hardware failures such as equipment or module damage and transmission line interruption, the core switch may also be paralyzed due to network traffic overload and excessive task load.

Therefore, if we want to ensure the stability of the network and ensure that important services are not interrupted, we must take necessary countermeasures. Usually, this measure is redundant connection, that is, multiple connections are created between the core switch and the backbone switch, as well as between the switch and the server.

Etherchannel is a technology developed by Cisco It aims to solve the communication problem between switches by grouping multiple fast Ethernet ports or gigabit Ethernet ports into one logical channel, so as to increase bandwidth and provide redundancy.

With this technology, multiple physical ports can be bound as a logical port. With multiple ports bound, existing ports can be fully used to increase bandwidth. Cisco switches allow up to 8 ports to be bound.

If it is Fast Ethernet, the total bandwidth can reach 1600Mbit/s; if it is Gbit Ethernet, the total bandwidth can reach 16Gbit/s. The bound port inherits the configuration mode of the original physical interface by default. Etherchannel does not support 10M port binding. Cisco switches can support both Layer 2 and Layer 3 Etherchannels. All ports in an Etherchannel must have the same rate and duplex mode. LACP can only be full duplex.

Etherchannel technology can be used to bundle ports of the same type. If there are multiple Etherchannel links between two switches, the spanning tree will block one of these links to avoid loops. When the spanning tree blocks one of the redundant links, it blocks an Etherchannel, and all the ports belonging to the Etherchannel link. On a Layer 3 switch, ports can be converted to routing ports. Etherchannel links can be created as Layer 3 links.

Etherchannel uses two management protocols to create a Port Channel. These protocols can ensure that when creating an Etherchannel, all port configurations are the same, and port rate, duplex mode, and VLAN information settings must be the same. After the channel is created, the administrator will modify the port configuration, and other ports will also be changed.

PAgP (Port Aggregation Protocol) is a private protocol of Cisco, which can be used to automatically create fast Etherchannel links. When using PAgP to configure the Etherchannel link, PAgP packets will be sent between ports that have enabled Etherchannel to negotiate the establishment of this channel. After PAgP identifies the matching Ethernet links, it will put them into an Etherchannel group. The spanning tree will regard Etherchannel as a separate bridge port.

LACP is a part of IEEE specification (802. ad). It can bundle many physical ports to establish an Ethernet channel. LACP enables the switch to send LACP packets to the peer to negotiate a bundled Etherchannel channel. This is similar to the process of establishing PAgp. Because LACP is an IEEE standard protocol, it can be used in hybrid networks. Both protocols are supported in Cisco environments.

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