Switch Port Aggregation with Ether Channel
Switches use Ethernet, fast Ethernet and gigabit Ethernet or 10 gigabit Ethernet port. We can add two or more link b/w two switches for increase the bandwidth. If we can add two link b/w two switches, will the bandwidth double because link acts independently, but STP will detect the loop and will place one of the port in blocking state. The end result is still a single active link between switches.
Cisco offers another method of scaling link bandwidth by aggrageting, or bundling parallel links, termed the Ether channel technology. Two to eight links of either fast Ethernet, gigabit Ethernet or 10-gigabitethernet, can be bundled as one logical link of the fastetherchannel (EFC), gigabitetherchannel (GEC) or 10-gigbitetherchannel (10 GEC). The bundle provide a full-duplex bandwidth of up to
1600 Mbps ( 8 link of fast Ethernet)
16gbps (8 link of gigabit Ethernet)
160gbps (8 link of 10 gigabit Ethernet)
EtherChannel also provides redundancy with several bundled physical links. If one of the links within the bundle fails, traffic sent through that link automatically moved to an adjacent link. Failover occurs in less than a few microsecond and is transparent to the end user.
Etherchannel bundle can consist of 8 physical ports of the same Ethernet media type and speed. All bundled ports first must be belong to the same VLAN. If used as a trunk bundled port must be in trunking mode, have the same native vlan, and pass the same set of vlan. Each port should have the same speed and duplex.
EtherChannel also provide the load balancing, means it filter traffic with all bundled EC. The load is not necessary balanced equally across all the links. Instead, frames are forwarded on a specific link as a result of hashing algorithm. The algorithm can use source IP address, destination IP, or a combination of source and destination IP address, source and destination MAC address, or TCP/UDP port number.
EtherChannel Negotiation protocols
There are two protocols used for negotiating etherchannel and link aggregation. We can configure in three ways in cisco switches.
1. Port Aggregation protocol (PAgP) : cisco proprietary protocol
2. IEEE link aggregation control protocol (LaCP): industry standard (IEEE 802.3ad)
3. Manual etherchannel configuration without any protocol.
Port Aggregation Protocol (PAgP)
It have two channel modes and they are “desirable” and “auto” mode.
Switch(config)# interface range fastethernet 0/1-3
Switch(config-range-if)# Switchport mode trunk
Switch(config-range-if)# Switchport trunk encapsulation dotq1
Switch(config-range-if)# channel-protocol pagp
Switch(config-range-if)# channel-group 1 mode desirable
Link Aggregation Control Protocol (LACP)
We can set system priority on port which have switch have lowest priority it become auto mode.
Switch(config)# lacp system-priority <priority>
Same as but use : channel-protocol lacp and channel-group 2 mode active and lacp port-priority <priority>