1. Implementing Spanning Tree
Module 3 - Part 4 Etherchannel
Jane Brooke (Centennial College) mods by Emerson Hunt

2. EtherChannel

3. About EtherChannel Logical aggregation of bandwidth
Viewed as one logical port
by STP, trunking, access and for administration
Bind ports
Yields 1600Mbps (FastEther) or 16Gbps(GigabitEther)
Load balancing algorithm differs by platform
Load balancing not frame by frame – usually by source and dest MAC address pairs
Allows for creation of very high-bandwidth logical links
Load balances among physical links involved
Provides automatic failover
Simplifies subsequent logical configuration
Configuration is per logical link instead of per physical link
Although any number up to 8 may be used, 2, 4, and 8 are most effective (because of the way load balancing works)
With LACP, more than 8 links can be placed in the bundle with extra links beyond 8 are "hot standby"

4. Etherchannel Benefits
Use all available bandwidth by logically “bundling” up to eight physical links
The logical Etherchannel can be managed as a single unit called a port channel or channel group
Seen as one by
Shutdown/no shutdown
Sh spanning tree
Sh interface trunking

5. Etherchannel Benefits
Load is balanced across physical links
Although balancing algorithm is not necessarily optimal
Under some circumstances balancing is uneven
Remaining links continue to operate if a member of the etherchannel bundle fails
Loss of a line in an etherchannel is not seen by STA
Failover time is only milliseconds

6. Used Where? L2 as trunk between two switches
L3 as connection between two routers
Access link
typically between switch and server with appropriate NICs (NIC "teaming")

7. Etherchannel and Servers
Multiple NICs can be installed in a server and a higher bandwidth aggregated link can be formed between the server and the switch
Known as ``nic teaming``
May not be supported natively by the server OS
Proper choice of the load balancing algorithm is important with NIC teaming

8. EtherChannel Dynamic Trunk Negotiation Protocols
PAgP
Cisco proprietary
Sends PAgP packets across link to negotiate EtherChannel
LACP
IEEE standard 802.3ad
Sends LACP packets across link to bundle multiple ports into a single channel
Use in mixed switch environment
Port Aggregation Protocol
Link aggregation control protocol

9. EtherChannel Interface Modes
ON – Forces EtherChannel ON without PAgP or LACP negotiation (not recommended)
PAgP
Auto (default PAgP mode)
interface enters passive negotiating state
responds to PAgP packets received but doesn’t initiate PAgP negotiation
Desirable (PAgP mode)
interface actively negotiates with other interfaces
PAgP packets are exchanged
LACP
Passive (Default LACP mode)
port responds to LACP packets received, but it does not initiate LACP packet negotiation
Active
port actively negotiates state with other ports by sending LACP packets
Recommendation is to use: (priority)
LACP active
PAGP desirable ON
Using the protocol instead of forcing ON is recommended as it implements additional Etherchannel functionality

10. The Defaults Auto for PAgP and passive for LACP Best practice is to
Means that by default, links WILL NOT aggregate automatically
Best practice is to
Explicitly set aggregation protocol using the channel-protocol command
manually configure using the channel-group command
PAgP is the proprietary default link aggregation protocol on Cisco switches
Use LACP for vendor neutrality

11. PAgP
PAgP packets sent between Etherchannel ports – negotiate forming channel
Etherchannel seen as single bridge port to spanning tree
Packets sent every 30 seconds
Multicast out MAC C-CC-CC-CC
Ensures all ports have same speed, duplex and VLAN info

12. The Rules All links in a channel-group must be almost identical
Speed and duplex
Switch port mode (trunk or access)
If access, belong to same vlan
If trunk, same vlans allowed
Each etherchannel must be assigned a channel group number (1-64)
Creates a Port-channel interface section in running config

13. Guidelines for Configuring EtherChannel

14. Guidelines for Configuring EtherChannel (Cont.)
Interfaces in the same bundle can support varying port costs

15. About EtherChannel Configuration Commands
Configure PAgP
interface range blah blah
channel-protocol pagp
channel-group X mode auto
Configure LACP
channel-protocol lacp
channel-group X mode active
Verify
show interfaces fastethernet 0/1 etherchannel
show etherchannel 1 port-channel
show etherchannel 1 summary

16. Configuring L2 EtherChannel
Specify the interfaces to configure in the bundle
Switch(config)#interface range interface slot/port - port
Specify the channel protocol either pagp OR lacp
Switch(config-if-range)#channel-protocol {pagp | lacp}
PAgP is default on Cisco switches.
Create the port-channel interface and place the interfaces as members
Switch(config-if-range)#channel-group number mode {auto | desirable | active | passive | on}

17. Verifying EtherChannel
Switch#show running-config interface port-channel num
Displays port-channel information
Switch#show run interface port-channel 1
Building configuration...
Current configuration : 66 bytes !
interface Port-channel1
switchport mode dynamic desirable
end
Switch#show running-config interface interface x/y
interface Port-channel2
switchport trunk encapsulation dot1q
switchport mode trunk
switchport nonegotiate
no ip address !
interface GigabitEthernet0/9
description DSW121 0/ DSW122 0/9-10
duplex full
speed 100
channel-group 2 mode desirable
interface GigabitEthernet0/10
Switch#show run interface gig 0/9 Building configuration...
Current configuration : 127 bytes !
interface GigabitEthernet 0/9
switchport mode dynamic desirable
channel-group 2 mode desirable
channel-protocol pagp
end
Displays interface information

18. Verifying EtherChannel (Cont.)
Switch#show interfaces gigabitethernet 0/9 etherchannel
Port state = Up Mstr In-Bndl
Channel group = Mode = Desirable-Sl Gcchange = 0
Port-channel = Po GC = 0x Pseudo port-channel = Po1
Port index = Load = 0x00
Flags: S - Device is sending Slow hello. C - Device is in Consistent state.
A - Device is in Auto mode P - Device learns on physical port.
d - PAgP is down.
Timers: H - Hello timer is running Q - Quit timer is running.
S - Switching timer is running. I - Interface timer is running.
Local information:
Hello Partner PAgP Learning Group
Port Flags State Timers Interval Count Priority Method Ifindex
Gi0/9 SC U6/S7 H s Any
Partner's information:
Partner Partner Partner Partner Group
Port Name Device ID Port Age Flags Cap.
Gi0/9 DSW e Gi0/ s SC
Age of the port in the current state: 00d:20h:00m:49s

19. Load Balancing
Etherchannel provides a choice of algorithms to determine which bundle member will carry a given frame
Various load-balancing methods are available (choices are platform dependant)
The default method may lead to some members being more heavily utilized than others

20. Example
Suppose we have an Etherchannel connecting a switch to a server
One type of algorithm depends solely on destination mac address
All frames destined for the same mac address will use the same wire
Therefore virtually all server bound frames will use just one wire in the etherchannel

21. Available Methods & which is the default vary by platform
Balancing Methods
src-ip
dst-ip
src-dst-ip
src-mac
dest-mac
src-dst-mac
src-port
dst-port
src-dst-port
Available Methods & which is the default vary by platform

22. Configuring EtherChannel Load Balancing
Switch(config)#port-channel load-balance type
Note that this is a global command
I.e. method cannot be configured on a per-channel basis
To see the current load balancing method, use the following:
Switch#show etherchannel load-balance Source XOR Destination IP address

23. Notes the default method will usually result in a fair balancing
the following command will give some sense of the fairness of the load balancing algorithm
show etherchannel port-channel X Look for the "load" value on each channel They should be similar

24. Resources

25. Personal Notes Etherchannel works (sort of) in Packet Tracer
I have had PT 5.1 crash when playing with multiple Etherchannels
Packet tracer definitely does not accurately simulate show command output where port channels are involved
However, etherchannel also seems a bit flakey on our equipment
Lab suggests "flapping" the interfaces if the Etherchannel does not come up