EtherChannel

1.1.d Introduction (Not on blueprint)

EtherChannel characteristics:

Logical aggregation of physical links between two switches (one-to-one connection)
Up to 8 active ports can be bundled into 1 logical EtherChannel
Every port has to have the same speed and duplex settings, no mixing possible
The configuration of the logical Port-Channel is inherited to the physical member interfaces
This is because in an EtherChannel each member interface must have the same configuration
If one (1) or several links fail, the Etherchannel will still be up with the remaining links (redundancy)
STP sees an EtherChannel as 1 logical port
STP will give the EtherChannel a higher cost if one or more links fail
Load sharing/balancing across bundled links is done by default with different possible algorithms (configurable)
Increase of bandwidth bandwidth
Different EtherChannel protocols (LACP, PAgP, manual/static) can’t be mixed
EtherChannels should always have a bundle of link numbers based on 2^x
Layer 2 EtherChannel can be in trunk or access mode
EtherChannels across two or more stacked switches are called Multichassis EtherChannel
Important: It’s a common misunderstanding that an EtherChannel doubles/triples/… the bandwidth for a single end user session. If every bundled link has 1G, a single end user session will still have a maximum bandwidth of 1G. This is because a single flow doesn’t split up between several links.
Important: STP sees an EtherChannel as 1 logical port. STP either blocks the whole EtherChannel or nothing but never one single link of an EtherChannel.

“EtherChannel” CLI configuration commands:

## Configuring an EtherChannel interface (trunk mode)
Switch(config)# interface port-channel <id>
Switch(config-if)# switchport mode trunk
Switch(config-if)# switchport trunk allowed vlan <vlan-ids>

## Configuring an EtherChannel interface (access mode)
Switch(config)# interface port-channel <id>
Switch(config-if)# switchport mode access
Switch(config-if)# switchport access vlan <vlan-id>

## Assigning EtherChannel to a range of interfaces
Switch(config)# interface range <if-range>
Switch(config-if)# channel-group <po-id> mode [active | passive | desirable | auto | on]

“EtherChannel” CLI show commands:

## Showing configuration of a specific EtherChannel
Switch# show interface port-channel <id>

## Showing configured EtherChannels, their used protocol and assigned ports
Switch# show etherchannel summary

## Showing configured EtherChannels and their technical details
Switch# show etherchannel port-channel

1.1.d i LACP, static

LACP

Link Aggregation Channel Protocol

General information on “LACP”:

Open standard
Also known as IEEE 802.1ax

How “LACP” works:

LACP does negotiation by sending LACP packets to its peer
LACP assigns a priority value to each port with EtherChannel capabilities
16 ports can be assigned to an LACP-based EtherChannel but only 8 with the lowest priority will be used
The remaining ports will only be bundled if an already bundled port fails

“LACP” characteristics:

LACP packets are sent every 30 seconds by default
LACP checks for configuration consistency and manages link additions and failures
Verifies that all physical and configurational conditions are consistent

“LACP” priorities:

System priority has a default of 32768, lower is better
If two connected LACP devices have the same priority (tie), the lower MAC address decides who is “the master”
Port priority has a default value of 32768, lower is better
Port priority makes sense when bundling more than 8 links together
If two or more ports have the same priority (tie), the lower Port ID wins

“LACP"modes:

LACP active: Interface is active, sends out LACP packets (does active negotiation)
LACP passive: Interface is passive, listens to LACP packets but doesn’t send them out

“LACP” channel mode interoperability:

Channel mode	Active	Passive
Active	Yes	Yes
Passive	Yes	No

“LACP” CLI configuration commands:

## Setting the EtherChannel mode to LACP
Switch(config)# interface range <if-range>
Switch(config-if)# channel-protocol lacp
Switch(config-if)# channel-group <po-id> mode [active | passive]
Switch(config-if)# lacp port-priority <value>

“LACP” CLI show commands:

## Showing LACP neighbors
Switch# show lacp neighbor

PAgP (not on blueprint)

Port Aggregation Protocol

General information on “PAgP”:

Cisco proprietary protocol

How “PAgP” works:

PAgP packets are sent between EtherChannel-capable ports to negotiate the forming of the channel
When PAgP identifies matched Ethernet links, it groups the links into an EtherChannel
The EtherChannel then gets added to STP as a single bridge port

“PAgP” characteristics:

PAgP packets are sent every 30 seconds by default
PAgP checks for configuration consistency and manges link additions and failures
Verifies that all physical and configurational conditions are consistent

“PAgP” modes:

PAgP desirable: Interface is active, sends out PAgP packets (does active negotiation).
PAgP auto: Interface is passive, listens to PAgP packets but doesn’t send them out.

“PAgP” channel mode interoperability:

Channel mode	Desirable	Auto
Desirable	Yes	Yes
Auto	Yes	No

“PAgP” CLI configuration commands:

## Setting the EtherChannel mode to PAgP
Switch(config)# interface range <if-range>
Switch(config-if)# channel-protocol pagp
Switch(config-if)# channel-group <po-id> mode [desirable | auto]

“PAgP” CLI show commands:

## Showing PAgP neighbors
Switch# show pagp neighbor

static

General information on “static”:

Manual (static) EtherChannel bypasses the negotiation process (LACP or PAgP)
Both sides must be configured in mode “on” to work

“static” characteristics:

Since there’s no negotiation, loops/packet loss/… can occur if only one side of the links is configured as static EtherChannel while the other side of the links aren’t configured for EtherChannel

“static” CLI configuration commands:

## Setting the EtherChannel mode to static
Switch(config)# interface range <if-range>
Switch(config-if)# channel-group <po-id> mode on

“static (EtherChannel)” CLI show commands:

## Showing configured EtherChannels, their used protocol and assigned ports
Switch# show etherchannel summary

1.1.d ii Layer 2, Layer 3

Layer 2

General Information on “Layer 2 EtherChannels”:

Layer 2 EtherChannels are used for Switching purposes
STP “sees” Layer 2 EtherChannels as one logical link

Layer 3

General Information on “Layer 3 EtherChannels”:

Layer 3 EtherChannels are used for Routing purposes
Therefore an IP needs to be assigned to the EtherChannel
The IP address must be configured on the logical Port-Channel interface and not on the physical member interfaces
STP will not be active since it’s Layer 3

1.1.d iii Load balancing

General Information on “Load balancing”:

Not pure load balancing but more like load distribution
Configured globally and not per EtherChannel
Load doesn’t get equally balanced over all bunded ports
Cisco proprietary hash algorithm runs on an EtherChannel with values from 0-7
Hash is calculated from fields in the packet header (see possible algorithms below)
Link count goes from 0 to 7 where 0 = Link 1 and 7 = Link 8
Per-flow balancing
The possible configurable algorithm types are platform-specific

“Load balancing” algorithm can be based on:

Source IP address
Destination IP address
Both source and destination IP address (XOR)
Source MAC address
Destination MAC address
Both source and destination MAC address (XOR)
TCP/UDP port numbers
[…] and more or less, depending on the platform […]

“Load balancing” issue:

Polarization = Always the same link will be used for the traffic
Polarization is an issue with “static” algorithms
“Static algorithms” = Algorithms where the information (source/destination MAC/IP) used to calculate the to-be-used-link always stays the same
Problem: Using only the source MAC address as algorithm uses always the same link for a specific host since MAC addresses are normally tied to a specific host and don’t change.
Solution: Using a “modern” algorithm which combines different variables such as source/destination MAC/IP + TCP/UDP port numbers.

“Load balacing” XOR-logic:

If the compared bits are the same, the result is 0
If the compared bits are different, then the result is 1
The last 1-3 bits are used to calculate the EtherChannel algorithm value (from left to right)

# of links in EtherChannel	# of lowest-order bits to XOR	possible results
2	1	0,1
4	2	0,1,2,3
8	3	0,1,2,3,4,5,6,7

“Load balancing” exact distribution:

# of links in EtherChannel	Load Balancing
8	1:1:1:1:1:1:1:1
7	2:1:1:1:1:1:1
6	2:2:1:1:1:1
5	2:2:2:1:1
4	2:2:2:2
3	3:3:2
2	4:4

“EtherChanel Load balancing” CLI configuration commands:

## Modify the EtherChannel load balancing algorithm
Switch(config)# port-channel load-balance <algorithm>

“EtherChanel Load balancing” CLI show commands:

## Showing the current set EtherChannel load balancing algorithm
Switch# show etherchannel load-balance

1.1.d iv EtherChannel Misconfiguration Guard

General information on “EtherChannel Misconfiguration Guard”:

Works only with LACP or PAgP
Prevents misconfiguration of EtherChannels
…and therefore prevents creating loops due to misconfigured EtherChannels
If a possible switching loop is detected, all ports of an EtherChannel are set into err-disabled state immediately
Possible misconfiguration issues: different parameters on both switches, one switch configured as EtherChannel while other is not, …

“EtherChannel Misconfiguration Guard” CLI configuration commands:

## Disabling/Enabling EtherChannel misconfiguration guard
Switch(config)# [no] spanning-tree etherchannel guard misconfig

“EtherChannel Misconfiguration Guard” CLI show commands:

## Showing the status of EtherChannel misconfiguration guard
Switch# show spanning-tree summary | in EtherChannel