4-4. Ether Channel

· You can aggregate several individual switch ports into a single logical port or Ether Channel.
· Fast Ethernet ports, when bundled together, form a Fast Ether Channel (FEC). Gigabit ports form a Gigabit Ether Channel (GEC).
· You can manually configure Ether Channels or aggregate them through the use of dynamic protocols. PAgP is a Cisco proprietary protocol, whereas Link Aggregation Control Protocol (LACP) is a standards-based protocol defined in IEEE 802.3ad (also known as IEEE 802.3 Clause 43, "Link Aggregation").
· Frames are distributed onto the individual ports that make up an Ether Channel by using a hashing algorithm. The algorithm can use source, destination, or a combination of source and destination IP addresses, source and destination MAC addresses, or TCP/UDP port numbers, depending on the hardware platform and configuration.
· Frame distribution is deterministic; that is, the same combination of addresses or port numbers always points to the same port within the Ether Channel.
· The frame distribution hashing algorithm performs an exclusive-OR (XOR) operation on one or more low-order bits of the addresses or TCP/UDP port numbers to select on which link a frame will be forwarded. For a two-port bundle, the last bit is used; a four-port bundle uses the last two bits; an eight-port bundle uses the last three bits. (With XOR, if two bits are identical, a 0 bit results; if two bits are different, a 1 bit results.)
· If a link within an Ether Channel fails, the traffic that normally crosses the failed link is moved to the remaining links.
· Ether Channel links can be static access ports or trunk ports. However, all links to be bundled must have consistent configurations before an Ether Channel can form