How to find LACP partner interface or port in Cisco Router and Switch?

Interface description is one of the most important configuration when bringing up interfaces between two devices. In a bundle or port-channel interface, there is a way to find the partner interface or which member in that bundle is your interface or port is connected especially if there’s no description or outdated.

Here are the steps and commands to find LACP partner interface or port in Cisco Router and Switch

Fig1.1 (Cisco IOS-XR)

Assuming we have this Fig1.1, two Cisco ASR9000 routers with 2 interfaces connected to each other and joined in a Bundle. We want to verify if the partner interface is correct or not.

Cisco-XR1
RP/0/RSP0/CPU0:Cisco-XR1# configure

interface Bundle-Ether100
description Bundle to Cisco-XR2
ipv4 address 192.168.0.1 255.255.255.252
load-interval 30
logging events link-status

interface Gi0/0/0/0
description  Connect to Gi0/0/0/2
bundle id 100 mode active
load-interval 30
dampening

interface Gi0/0/0/1
description  Connect to Gi0/0/0/0
bundle id 100 mode active
load-interval 30
dampening

Cisco-XR2
RP/0/RSP0/CPU0:Cisco-XR2# configure

interface Bundle-Ether100
description Bundle to Cisco-XR1
ipv4 address 192.168.0.2 255.255.255.252
load-interval 30
logging events link-status

interface Gi0/0/0/2
description  Connect to Gi0/0/0/0
bundle id 100 mode active
load-interval 30
dampening

interface Gi0/0/0/0
description  Connect to Gi0/0/0/1
bundle id 100 mode active
load-interval 30
dampening

Verification:

As you can see Gi0/0/0/0 connects to Gi0/0/0/2; and Gi0/0/1 is connected to Gi0/0/0/0, but how verify if these are correct or not. Use these commands in the bundle interface:

show lacp <interface>

Example:

Cisco-XR1
RP/0/RSP0/CPU0:Cisco-XR1#show lacp Bundle-ether 100

State: a – Port is marked as Aggregatable.
s – Port is Synchronized with peer.
c – Port is marked as Collecting.
d – Port is marked as Distributing.
A – Device is in Active mode.
F – Device requests PDUs from the peer at fast rate.
D – Port is using default values for partner information.
E – Information about partner has expired.

Bundle-Ether100

Port (rate) State Port ID Key System ID
——————– ——– ————- —— ————————
Local
Gi0/0/0/0 30s ascdA— 0x8000,0x000c 0x0048 0x8000,aa-bb-cc-dd-ee-ff
Partner 30s ascdA— 0x8000,0x001b 0x0048 0x8000,00-11-22-33-44-55
Gi0/0/0/1 30s ascdA— 0x8000,0x0050 0x0048 0x8000,a1-b2-c3-d4-e5
Partner 30s ascdA— 0x8000,0x0019 0x0048 0x8000,00-66-77-88-99-00

Port Receive Period Selection Mux A Churn P Churn
——————– ———- —— ———- ——— ——- ——-
Local
Gi0/0/0/0 Current Slow Selected Distrib None None
Gi0/0/0/1 Current Slow Selected Distrib None None

Cisco-XR2
RP/0/RSP0/CPU0:Cisco-XR2#show lacp bundle-ether 100
Tue Apr 11 14:21:46.786 SGP
State: a – Port is marked as Aggregatable.
s – Port is Synchronized with peer.
c – Port is marked as Collecting.
d – Port is marked as Distributing.
A – Device is in Active mode.
F – Device requests PDUs from the peer at fast rate.
D – Port is using default values for partner information.
E – Information about partner has expired.

Bundle-Ether100

Port (rate) State Port ID Key System ID
——————– ——– ————- —— ————————
Local
Gi0/0/0/2 30s ascdA— 0x8000,0x001b 0x0048 0x8000,00-11-22-33-44-55
Partner 30s ascdA— 0x8000,0x000c 0x0048 0x8000,aa-bb-cc-dd-ee-ff

Gi0/0/0/0 30s ascdA— 0x8000,0x0019 0x0048 0x8000,00-66-77-88-99-00
Partner 30s ascdA— 0x8000,0x0050 0x0048 0x8000,a1-b2-c3-d4-e5

Or you can do filtering to easily find.

RP/0/RSP0/CPU0:Cisco-XR2#show lacp bundle-ether 100 | i “0x8000,0x001b 0x0048 0x8000,00-11-22-33-44-55”
Gi0/0/0/2 30s ascdA— 0x8000,0x001b 0x0048 0x8000,00-11-22-33-44-55

RP/0/RSP0/CPU0:Cisco-XR2#show lacp bundle-ether 100 | i “0x8000,0x0019 0x0048 0x8000,00-66-77-88-99-00”
Gi0/0/0/0 30s ascdA— 0x8000,0x0019 0x0048 0x8000,00-66-77-88-99-00

or simply “show lacp” the physical interface

show lacp <interface>

Cisco-XR1
RP/0/RSP0/CPU0:Cisco-XR1#show lacp Gi0/0/0/0

State: a – Port is marked as Aggregatable.
s – Port is Synchronized with peer.
c – Port is marked as Collecting.
d – Port is marked as Distributing.
A – Device is in Active mode.
F – Device requests PDUs from the peer at fast rate.
D – Port is using default values for partner information.
E – Information about partner has expired.

Bundle-Ether100

Port (rate) State Port ID Key System ID
——————– ——– ————- —— ————————
Local
Gi0/0/0/0 30s ascdA— 0x8000,0x000c 0x0048 0x8000,aa-bb-cc-dd-ee-ff
Partner 30s ascdA— 0x8000,0x001b 0x0048 0x8000,00-11-22-33-44-55

Port Receive Period Selection Mux A Churn P Churn
——————– ———- —— ———- ——— ——- ——-
Local
Gi0/0/0/0 Current Slow Selected Distrib None None

Fig2.1 (Cisco NexusOS)

show lacp interface <physical interface>

show lacp neighbor interface <physical interface>

show lacp neighbor interface <port-channel interface>

Example:
From the example, you can see that:
Switch1 Mac address: aa-11-bb-22-cc-33
Switch2 Mac address: dd-44-ee-55-ff-66

Switch1
Switch1# show lacp interface e1/2
Interface Ethernet1/2 is up
Channel group is 100 port channel is Po100
Local Port: Eth1/2 MAC Address= aa-11-bb-22-cc-33
System Identifier=0x8000, Port Identifier=0x8000,0x401

Switch1# show lacp neighbor interface e1/2
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
Ethernet1/2 neighbors
Partner’s information
Partner Partner Partner
Port System ID Port Number Age Flags
Eth1/2 32768,dd-44-ee-55-ff-660x401 36418520 SA

Switch1# show lacp neighbor interface Po100
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
port-channel100 neighbors
Partner’s information
Partner Partner Partner
Port System ID Port Number Age Flags
Eth1/2 32768,dd-44-ee-55-ff-660x401 36418348 SA

Switch2
Switch2# show lacp interface e1/2
Interface Ethernet1/2 is up
Channel group is 100 port channel is Po100
Local Port: Eth1/2  MAC Address= dd-44-ee-55-ff-66
System Identifier=0x8000, Port Identifier=0x8000,0x401

Switch2# show lacp neighbor interface port-channel 100
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
port-channel100 neighbors
Partner’s information
Partner Partner Partner
Port System ID Port Number Age Flags
Eth1/2 32768,aa-11-bb-22-cc-330x401 36418041 SA