Configuring Layer 2 etherchannel using LACP auto negotiation (With all auto default settings turn off)

Configuring Layer 2 etherchannel using LACP auto negotiation (With all auto default settings turn off)

by Cyrus Lok on Sunday, May 30, 2010 at 3:19am

I am going to start simple with one 3550-1 and 2950-1 as starters, I have found connecting everything on all 4 switches and configuring makes me difficult to keep up…

There will be 3 cables connecting each other.

Look at the cdp neighbour output:

2950-1#sh cdp neig
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge
S – Switch, H – Host, I – IGMP, r – Repeater, P – Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID
3550-1 Fas 0/3 145 S I WS-C3550-2Fas 0/5
3550-1 Fas 0/2 134 S I WS-C3550-2Fas 0/3
3550-1 Fas 0/1 173 S I WS-C3550-2Fas 0/1

3550-1#sh cdp neigh
Capability Codes: R – Router, T – Trans Bridge, B – Source Route Bridge
S – Switch, H – Host, I – IGMP, r – Repeater, P – Phone

Device ID Local Intrfce Holdtme Capability Platform Port ID
2950-1 Fas 0/5 128 S I WS-C2950- Fas 0/3
2950-1 Fas 0/3 128 S I WS-C2950- Fas 0/2
2950-1 Fas 0/1 128 S I WS-C2950- Fas 0/1

Turn off all default auto settings:

2950-1(config)#int range fa0/1 – 3
2950-1(config-if-range)#speed 100
2950-1(config-if-range)#duplex full
2950-1(config-if-range)#switchport mode trunk
2950-1(config-if-range)#switchport nonegotiate

Well because 3550-1 ports are all set to duplex auto and speed auto, there will be duplex and speed mismatch, etherchannel will not be able to configure if there’s mismatch.

Syslog level 4 warning messages:
00:55:44: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/1 (not half duplex), with 3550-1 FastEthernet0/1 (half duplex).
00:55:44: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/2 (not half duplex), with 3550-1 FastEthernet0/3 (half duplex).
00:55:44: %CDP-4-DUPLEX_MISMATCH: duplex mismatch discovered on FastEthernet0/3 (not half duplex), with 3550-1 FastEthernet0/5 (half duplex).

I strongly recommend you to use logging synchronous command, because by hardcoding the configuration cisco switches will keep sending syslog messages that will cut your command into unreadable status!

3550-1(config)#int range fa0/1 , fa0/3, fa0/5
3550-1(config-if-range)#speed 100
3550-1(config-if-range)#duplex full

Note: If encapsulation is at auto negotiation you will not be able to hardcode the port into a trunk.
3550-1(config-if-range)#switchport trunk encapsulation dot1q
3550-1(config-if-range)#switchport mode trunk
3550-1(config-if-range)#switchport nonegotiate

using nonegotiate keyword makes rogue switch unable to negotiate a trunk automatically, usually newly out of the box switch will be dynamic desirable which will proactively negotiate a trunk with another switch.

3550-1(config-if-range)#description Connects to 2950-1

Always the best practice to put description for ease of troubleshooting.

Now I will start configuring LACP (802.3AD) auto-negotiation.

3550-1(config-if-range)#channel-protocol lacp

LACP is the standard that can be used by mixed vendor switches, whereas PAgP can only be used by Cisco specific switches. For scalability it is recommended to use LACP instead of PAgP as both of these protocols do not have significant advantages over each other.

3550-1(config-if-range)#channel-group ?
<1-64> Channel group number

MLS has more channel group choices of up to 64 channels.

3550-1(config-if-range)#channel-group 1 mode active
Creating a port-channel interface Port-channel 1

Active keyword is used for LACP, meaning this channel group of 3550-1 will proactively negotiating using LACP to form an etherchannel group 1.

For PAgP the equivalent of Active is Desirable, and the equivalent of Passive is Auto.

2950-1(config-if-range)#channel-protocol lacp
2950-1(config-if-range)#channel-group 1 mode passive
Creating a port-channel interface Port-channel 1

Using Active is fine as well, passive is waiting for Active group to negotiate an etherchannel using LACP.

Syslog appearing from 2950-1

01:08:48: %LINK-3-UPDOWN: Interface Port-channel1, changed state to up
01:08:49: %LINEPROTO-5-UPDOWN: Line protocol on Interface Port-channel1, changed state to up
2950-1(config-if-range)#
01:08:50: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to up
2950-1(config-if-range)#
01:08:53: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/2, changed state to up
2950-1(config-if-range)#
2950-1(config-if-range)#
01:09:08: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to down
2950-1(config-if-range)#
01:09:14: %LINEPROTO-5-UPDOWN: Line protocol on Interface FastEthernet0/3, changed state to up

Use show etherchannel port to show details of each member of the ports of an etherchannel.

2950-1#sh etherchannel port
Channel-group listing:
———————-

Group: 1
———-
Ports in the group:
——————-
Port: Fa0/1
————

Port state = Up Mstr In-Bndl
Channel group = 1 Mode = Passive Gcchange = –
Port-channel = Po1 GC = – Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = LACP

Flags: S – Device is sending Slow LACPDUs F – Device is sending fast LACPDUs.
A – Device is in active mode. P – Device is in passive mode.

Local information:
LACP port Admin Oper Port Port
Port Flags State Priority Key Key Number State
Fa0/1 SP bndl 32768 0x1 0x1 0x1 0x3C

Partner’s information:

LACP port Oper Port Port
Port Flags Priority Dev ID Age Key Number State
Fa0/1 SA 32768 000b.be08.f480 23s 0x1 0x2 0x3D

Age of the port in the current state: 0d:00h:02m:03s

Port: Fa0/2
————

Port state = Up Mstr In-Bndl
Channel group = 1 Mode = Passive Gcchange = –
Port-channel = Po1 GC = – Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = LACP

Flags: S – Device is sending Slow LACPDUs F – Device is sending fast LACPDUs.
A – Device is in active mode. P – Device is in passive mode.

Local information:
LACP port Admin Oper Port Port
Port Flags State Priority Key Key Number State
Fa0/2 SP bndl 32768 0x1 0x1 0x2 0x3C

Partner’s information:

LACP port Oper Port Port
Port Flags Priority Dev ID Age Key Number State
Fa0/2 SA 32768 000b.be08.f480 5s 0x1 0x4 0x3D

Age of the port in the current state: 0d:00h:02m:06s

Port: Fa0/3
————

Port state = Up Mstr In-Bndl
Channel group = 1 Mode = Passive Gcchange = –
Port-channel = Po1 GC = – Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = LACP

Flags: S – Device is sending Slow LACPDUs F – Device is sending fast LACPDUs.
A – Device is in active mode. P – Device is in passive mode.

Local information:
LACP port Admin Oper Port Port
Port Flags State Priority Key Key Number State
Fa0/3 SP bndl 32768 0x1 0x1 0x3 0x3C

Partner’s information:

LACP port Oper Port Port
Port Flags Priority Dev ID Age Key Number State
Fa0/3 SA 32768 000b.be08.f480 13s 0x1 0x6 0x3D

Age of the port in the current state: 0d:00h:01m:58s

As can be observed from the above information, it even show the port priority which is used for spanning tree for root bridge election. State bndl means they are all bundled together.

For a brief information of etherchannel use show etherchannel summary

2950-1#sh etherchannel summ
Flags: D – down P – in port-channel
I – stand-alone s – suspended
H – Hot-standby (LACP only)
R – Layer3 S – Layer2
u – unsuitable for bundling
U – in use f – failed to allocate aggregator
d – default port

Number of channel-groups in use: 1
Number of aggregators: 1

Group Port-channel Protocol Ports
——+————-+———–+———————————————–
1 Po1(SU) LACP Fa0/1(Pd) Fa0/2(P) Fa0/3(P)

For a verbose of etherchannel information use show etherchannel detail

2950-1#sh etherchannel detail
Channel-group listing:
———————-

Group: 1
———-
Group state = L2
Ports: 3 Maxports = 16
Port-channels: 1 Max Port-channels = 16
Protocol: LACP
Ports in the group:
——————-
Port: Fa0/1
————

Port state = Up Mstr In-Bndl
Channel group = 1 Mode = Passive Gcchange = –
Port-channel = Po1 GC = – Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = LACP

Flags: S – Device is sending Slow LACPDUs F – Device is sending fast LACPDUs.
A – Device is in active mode. P – Device is in passive mode.

Local information:
LACP port Admin Oper Port Port
Port Flags State Priority Key Key Number State
Fa0/1 SP bndl 32768 0x1 0x1 0x1 0x3C

Partner’s information:

LACP port Oper Port Port
Port Flags Priority Dev ID Age Key Number State
Fa0/1 SA 32768 000b.be08.f480 17s 0x1 0x2 0x3D

Age of the port in the current state: 0d:00h:05m:50s

Port: Fa0/2
————

Port state = Up Mstr In-Bndl
Channel group = 1 Mode = Passive Gcchange = –
Port-channel = Po1 GC = – Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = LACP

Flags: S – Device is sending Slow LACPDUs F – Device is sending fast LACPDUs.
A – Device is in active mode. P – Device is in passive mode.

Local information:
LACP port Admin Oper Port Port
Port Flags State Priority Key Key Number State
Fa0/2 SP bndl 32768 0x1 0x1 0x2 0x3C

Partner’s information:

LACP port Oper Port Port
Port Flags Priority Dev ID Age Key Number State
Fa0/2 SA 32768 000b.be08.f480 20s 0x1 0x4 0x3D

Age of the port in the current state: 0d:00h:05m:46s

Port: Fa0/3
————

Port state = Up Mstr In-Bndl
Channel group = 1 Mode = Passive Gcchange = –
Port-channel = Po1 GC = – Pseudo port-channel = Po1
Port index = 0 Load = 0x00 Protocol = LACP

Flags: S – Device is sending Slow LACPDUs F – Device is sending fast LACPDUs.
A – Device is in active mode. P – Device is in passive mode.

Local information:
LACP port Admin Oper Port Port
Port Flags State Priority Key Key Number State
Fa0/3 SP bndl 32768 0x1 0x1 0x3 0x3C

Partner’s information:

LACP port Oper Port Port
Port Flags Priority Dev ID Age Key Number State
Fa0/3 SA 32768 000b.be08.f480 2s 0x1 0x6 0x3D

Age of the port in the current state: 0d:00h:05m:31s

Port-channels in the group:
—————————

Port-channel: Po1 (Primary Aggregator)

————

Age of the Port-channel = 0d:00h:06m:04s
Logical slot/port = 1/0 Number of ports = 3
HotStandBy port = null
Port state = Port-channel Ag-Inuse
Protocol = LACP

Ports in the Port-channel:

Index Load Port EC state No of bits
——+——+——+——————+———–
0 00 Fa0/1 Passive 0
0 00 Fa0/2 Passive 0
0 00 Fa0/3 Passive 0

Time since last port bundled: 0d:00h:05m:33s Fa0/3
Time since last port Un-bundled: 0d:00h:05m:35s Fa0/3

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