Implementing Spanning
Tree
Module 3 - Part 4
Etherchannel
Jane Brooke (Centennial College)
mods by Emerson Hunt
EtherChannel
About EtherChannel

Logical aggregation of
bandwidth
 Viewed as one logical port


Bind 2 - 8 ports


by STP, trunking, access
and for administration
Yields 1600Mbps
(FastEther) or
16Gbps(GigabitEther)
Load balancing algorithm
differs by platform
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
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
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")
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
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
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
The Defaults

Auto for PAgP and passive for LACP


Best practice is to



Means that by default, links WILL NOT aggregate
automatically
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
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 01-00-0C-CC-CC-CC
Ensures all ports have same speed, duplex
and VLAN info
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
Guidelines for Configuring
EtherChannel
Guidelines for Configuring
EtherChannel (Cont.)
Interfaces in the same bundle can support varying port
costs
About EtherChannel
Configuration Commands

Configure PAgP
interface range blah blah
channel-protocol pagp
channel-group X mode auto

Configure LACP
interface range blah blah
channel-protocol lacp
channel-group X mode active
Verify
show interfaces fastethernet 0/1 etherchannel
show etherchannel 1 port-channel
show etherchannel 1 summary
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}
Verifying EtherChannel
Switch#show running-config interface port-channel num
• Displays port-channel information
Switch#show run interface portchannel 1
Building configuration...
Current configuration : 66 bytes
!
interface Port-channel1
switchport mode dynamic desirable
end
Switch#show running-config interface interface x/y
• Displays interface information
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
Verifying EtherChannel (Cont.)
Switch#show interfaces gigabitethernet 0/9 etherchannel
Port state
= Up Mstr In-Bndl
Channel group = 1
Mode = Desirable-Sl
Gcchange = 0
Port-channel = Po2
GC
= 0x00020001
Pseudo port-channel = Po1
Port index
= 0
Load = 0x00
Flags:
S
A
d
Timers: H
S
-
Device is sending Slow hello.
Device is in Auto mode.
PAgP is down.
Hello timer is running.
Switching timer is running.
C - Device is in Consistent state.
P - Device learns on physical port.
Q - Quit timer is running.
I - Interface timer is running.
Local information:
Port
Gi0/9
Flags State
SC
U6/S7
Timers
H
Hello
Partner PAgP
Interval Count
Priority
30s
1
128
Learning Group
Method Ifindex
Any
15
Partner's information:
Port
Gi0/9
Partner
Name
DSW122
Partner
Device ID
0005.313e.4780
Partner
Port
Gi0/9
Age of the port in the current state: 00d:20h:00m:49s
Partner Group
Age Flags
Cap.
18s SC
20001
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
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
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
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
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
Resources
 http://networkers-
online.com/blog/2008/07/etherchannelload-balancing-case-study/
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