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Network Engineer — 03. EtherChannel

2025-08-20 Networking EtherChannel LACP PAgP Cisco

Lab: Configuring EtherChannel

Topology

EtherChannel topology

Addressing table

DeviceInterfaceIP addressSubnet Mask
S1VLAN 99192.168.99.11255.255.255.0
S2VLAN 99192.168.99.12255.255.255.0
S3VLAN 99192.168.99.13255.255.255.0
PC-ANIC192.168.10.1255.255.255.0
PC-BNIC192.168.10.2255.255.255.0
PC-CNIC192.168.10.3255.255.255.0

Goals

  • Part 1. Configure basic switch parameters
  • Part 2. Configure PAgP EtherChannel (S1–S3)
  • Part 3. Configure LACP EtherChannel (S1–S2 and S2–S3)

Part 1 — Basic switch setup

S1

enable
conf t
hostname S1
no ip domain-lookup
enable secret class
banner motd "Unauthorized access is strictly prohibited!"
line console 0
exec-timeout 0 0
password cisco
logging synchronous
login
exit
line vty 0 15
password cisco
login
exit
interface range f0/1-24, g0/1-2
shutdown
exit
vlan 10
name Staff
vlan 99
name Management
exit
interface vlan 99
ip address 192.168.99.11 255.255.255.0
no shutdown
exit
interface f0/6
switchport mode access
switchport access vlan 10
no shutdown
do copy run start
end
copy running-config startup-config
S2

enable
conf t
hostname S2
no ip domain-lookup
enable secret class
banner motd "Unauthorized access is strictly prohibited!"
line console 0
exec-timeout 0 0
password cisco
logging synchronous
login
exit
line vty 0 15
password cisco
login
exit
interface range f0/1-24, g0/1-2
shutdown
exit
vlan 10
name Staff
vlan 99
name Management
exit
interface vlan 99
ip address 192.168.99.12 255.255.255.0
no shutdown
exit
interface f0/18
switchport mode access
switchport access vlan 10
no shutdown
do copy run start
end
copy running-config startup-config
S3

enable
conf t
hostname S3
no ip domain-lookup
enable secret class
banner motd "Unauthorized access is strictly prohibited!"
line console 0
exec-timeout 0 0
password cisco
logging synchronous
login
exit
line vty 0 15
password cisco
login
exit
interface range f0/1-24, g0/1-2
shutdown
exit
vlan 10
name Staff
vlan 99
name Management
exit
interface vlan 99
ip address 192.168.99.13 255.255.255.0
no shutdown
exit
interface f0/18
switchport mode access
switchport access vlan 10
no shutdown
do copy run start
end
copy running-config startup-config

Part 2 — PAgP EtherChannel (S1–S3)

PAgP (Port Aggregation Protocol) is a Cisco proprietary protocol. Modes: desirable (active negotiation) and auto (passive). At least one side must be desirable.

S1

enable
configure terminal
interface range f0/3-4
channel-group 1 mode desirable
switchport mode trunk
switchport trunk native vlan 99
no shutdown
exit
interface port-channel 1
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 1,10,99
end
copy running-config startup-config
S3

enable
configure terminal
interface range f0/3-4
channel-group 1 mode auto
switchport mode trunk
switchport trunk native vlan 99
no shutdown
exit
interface port-channel 1
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 1,10,99
end
copy running-config startup-config

Verify:

show etherchannel summary
S1 output

enable
configure terminal
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      N - not in use, no aggregation
        f - failed to allocate aggregator

    M - not in use, no aggregation due to minimum links not met
    u - unsuitable for bundling
    w - waiting to be aggregated
    d - default port

    A - formed by Auto LAG

Number of channel-groups in use: 1
Number of aggregators: 1
Group Port-channel Protocol Ports
——+————-+———–+———————————————-
1 Po1(SU) PAgP Et1/2(P) Et1/3(P)
end
copy running-config startup-config

Flag meanings: SU — channel is a Layer2 trunk and in use. P — port is bundled in the port-channel.

Verify STP — S3’s root port should now be Port-channel1:

show spanning-tree
S3 output

enable
configure terminal
VLAN0001
  Spanning tree enabled protocol ieee
  Root ID    Priority    32769
             Address     aabb.cc00.1000
             Cost        56
             Port        65 (Port-channel1)
             Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec

Bridge ID  Priority    32769  (priority 32768 sys-id-ext 1)
Address     aabb.cc00.3000
Hello Time   2 sec  Max Age 20 sec  Forward Delay 15 sec
Aging Time  300 sec


Interface           Role Sts Cost      Prio.Nbr Type




Po1                 Root FWD 56        128.65   P2p
end
copy running-config startup-config

Part 3 — LACP EtherChannel (S1–S2 and S2–S3)

LACP (Link Aggregation Control Protocol) is an open standard (IEEE 802.3ad). Modes: active (sends LACP frames) and passive (responds only). At least one side must be active.

S1–S2 (channel-group 2)

S1

enable
configure terminal
interface range f0/1-2
channel-group 2 mode active
switchport mode trunk
switchport trunk native vlan 99
no shutdown
exit
interface port-channel 2
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 1,10,99
end
copy running-config startup-config
S2

enable
configure terminal
interface range f0/1-2
channel-group 2 mode passive
switchport mode trunk
switchport trunk native vlan 99
no shutdown
exit
interface port-channel 2
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 1,10,99
end
copy running-config startup-config

S2–S3 (channel-group 3)

S2

enable
configure terminal
interface range f0/3-4
channel-group 3 mode active
switchport mode trunk
switchport trunk native vlan 99
no shutdown
exit
interface port-channel 3
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 1,10,99
end
copy running-config startup-config
S3

enable
configure terminal
interface range f0/1-2
channel-group 3 mode passive
switchport mode trunk
switchport trunk native vlan 99
no shutdown
exit
interface port-channel 3
switchport mode trunk
switchport trunk native vlan 99
switchport trunk allowed vlan 1,10,99
end
copy running-config startup-config

Verify all channels are up:

show etherchannel summary
S1

enable
configure terminal
Number of channel-groups in use: 2
Number of aggregators:           2

Group  Port-channel  Protocol    Ports
——+————-+———–+———————————————-
1      Po1(SU)           PAgP   Et1/2(P) Et1/3(P)
2      Po2(SU)           LACP   Et0/1(P) Et0/2(P)
end
copy running-config startup-config

S2

enable
configure terminal
Group  Port-channel  Protocol    Ports
------+-------------+-----------+----------------------------------------------
2      Po2(SU)           LACP   Fa0/1(P) Fa0/2(P)
3      Po3(SU)           LACP   Fa0/3(P) Fa0/4(P)
end
copy running-config startup-config
S3

enable
configure terminal
Group  Port-channel  Protocol    Ports
------+-------------+-----------+----------------------------------------------
1      Po1(SU)           PAgP   Et1/2(P) Et1/3(P)
3      Po3(SU)           LACP   Fa0/1(P) Fa0/2(P)
end
copy running-config startup-config

Verify connectivity — ping between PCs in VLAN 10:

PC-A> ping 192.168.10.2
PC-A> ping 192.168.10.3

Network Engineer Course | Lab 03

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