EtherChannel – Port Link Aggregation

EtherChannel or other vendors call this Smartgroup, is  a port link aggregation technology. In other words, a technology which is used to combine several physical links between switches or routers into one logical connection and treat them as single link.

A connection with a single link.

switch, etherchannel

Add another link to get more than 1 Gbps will not work, because Spanning-tree protocol (STP) will block redundant links to prevent a loop.

etherchannel, stp, spanning-tree

EtherChannel bundles the physical links into 1 logical link, and STP will not block any links. EtherChannel also does load balancing , if a link within the EtherChannel fails, traffic previously carried over the failed link is carried over the remaining links within the EtherChannel.

etherchannel

EtherChannel also works well on router connections. When an EtherChannel is created, a logical interface will be created, and we can configure the logical interface, for example assign access/trunk mode on switches and assign IP address  for that interface on routers.

Three mechanisms to configure EtherChannel :

  • Port Aggregation Protocol (PAgP).
  • Link Aggregation Control Protocol (LACP).
  • Static (mode ON).

Port Aggregation Protocol (PAgP)

PAgP is a Cisco proprietary protocol, this protocol dynamically negotiates the formation of a channel.
There are 2 PAgP modes :

pagp mode, pagp, etherchannel

The EtherChannel will be formed or not for PAgP :

pagp, pagp formed, etherchannel

Link Aggregation Protocol (LACP)

LACP is a IEEE Standard (IEEE 802.3ad) and this is the most common dynamic link aggregation protocol.
There are 2 LACP modes :

lacp modes, etherchannel, lacp, smartgroup

The EtherChannel will be formed or not for LACP :

lacp, lacp formed, etherchannel, smartgroup

Static (mode ON)

No negotiation needed in this mode. When using this mode make sure the other end must use this mode too.

Also read : Configuring an EtherChannel Link

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