ETHERCHANNEL: WHAT, LACP, PAgP, LAYER 2 & 3


REFERENCE LINK

http://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3550/software/release/12-1_8_ea1/configuration/guide/3550scg/swethchl.html

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TOPICS

UNDERSTANDING ETHERCHANNEL

LACP Vs PAgP MODES

LAYER 2 Vs LAYER 3 ETHERCHANNEL

LAYER 3 ETHERCHANNEL CONFIGURATION

LAYER 2 ETHERCHANNEL CONFIGURATION

 

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UNDERSTANDING ETHERCHANNEL

What: Etherchannel is the bundling of the individual links connected between two devices, to form a single logical link

Benefit is to get more Bandwidth over a single link and to get redundancy

Example : “The EtherChannel provides full-duplex bandwidth up to 800 Mbps (Fast EtherChannel) or 8 Gbps (Gigabit EtherChannel) between your switch and another switch or host

 

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LACP Vs PAgP MODES

These are the negotition protocols to form Etherchannel

 

LACP MODES(STANDARD BASED)

on: the link aggregation is forced to be formed without any LACP negotiation. A port-channel is formed only if the peer port is also in “on” mode. 
off: disable LACP and prevent ports to form a port-channel
passive: the switch does not initiate the channel, but does understand incoming LACP packets
active: send LACP packets and willing to form a port-channel

PAgP MODES(Cisco-proprietary solution)

on: The link aggregation is forced to be formed without any PAgP negotiation. A port-channel is formed only if the peer port is also in “on” mode. 
off: disable PAgP and prevent ports to form a port-channel
desirable: send PAgP packets and willing to form a port-channel
auto: does not start PAgP packet negotiation but responds to PAgP packets it receives


 

LAYER 2 Vs LAYER 3 ETHERCHANNEL

1. LOGICAL INTERFACE CREATION

With Layer 3, Logical interface has to be created, Command: ” interface port-channel “

With Layer 2, Logical interface is dynamically created

 

2. ASSIGNING INTERFACE TO ETHERCHANNEL

With both Layer 3 and 2 interfaces, you manually assign an interface to the EtherChannel

Command: ” channel-group interface configuration command

 

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LAYER 3 ETHERCHANNEL CONFIGURATION

1. LOGICAL INTERFACE CREATION

Example

Switch# configure terminal

Switch(config)# interface port-channel 5

Switch(config-if)# no switchport

Switch(config-if)# ip address 172.10.20.10 255.255.255.0

Switch(config-if)# end

 

2. ASSIGNING INTERFACE TO PORT CHANNEL

Example

Switch# configure terminal

Switch(config)# interface range gigabitethernet0/4 -5

Switch(config-if-range)# no ip address

Switch(config-if-range)# channel-group 5 mode desirable  /PAgp enabled with Desirable mode/

Switch(config-if-range)# end

 

POINT TO NOTE

While assigning IP to Etherchannel or Logical interface, we should not assign IP to individual interfaces

 

HOW TO CONFIRM DETAILS

Command: ” sh etherchannel summary ”

Example Output

Cat6500#show etherchannel summary 
Flags:  D - down        P - in port-channel
I - stand-alone s - suspended
R - Layer3      S - Layer2
U - port-channel in use
Group Port-channel  Ports
-----+------------+-----------------------------------------------------------
1     Po1(SU)     Fa4/2(P)   Fa4/3(P)   Fa4/4(P)   Fa4/5(P)

Port States
Description

bundled

The port is part of an EtherChannel and can send and receive BPDUs and data traffic.

suspended

The port is not part of an EtherChannel. The port can receive BPDUs but cannot send them. Data traffic is blocked.

standalone

The port is not bundled in an EtherChannel. The port functions as a standalone data port. The port can send and receive BPDUs and data traffic.

Note When one end of an EtherChannel has more members than the other, the unmatched ports enter the standalone state. In a topology that is not protected from Layer 2 loops by the spanning tree protocol(STP), a port in the standalone state can cause significant network errors. For LACP EtherChannels with Release 12.2(33)SXI3 and later releases, you can enter the port-channel standalone-disable interface configuration mode command to put ports into the suspended state instead of the standalone state. See the “Configuring LACP Port-Channel Standalone Disable” section.

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LAYER 2 ETHERCHANNEL CONFIGURATION

1. ASSIGNING INTERFACE TO ETHERCHANNEL

Example

Switch# configure terminal

Switch(config)# interface range gigabitethernet0/4 -5

Switch(config-if-range)# switchport mode access

Switch(config-if-range)# switchport access vlan 10

Switch(config-if-range)# channel-group 5 mode desirable

Switch(config-if-range)# end

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