Cisco IOS Ether-Channel Configuration

Brief

Ether-Channel allows multiple physical Ethernet links to combine into one logical channel. This allows load sharing of traffic among the links in the channel as well as redundancy in the event that one or more links in the channel fail. Ether-Channel can be used to interconnect LAN switches, routers, servers, and clients via unshielded twisted pair (UTP) wiring or single-mode and multimode fiber.

Guidelines

     1. All physical interfaces, which belong to the same logical interface (port-channel) on the same switch, must be with the same physical characteristic (all Fast-Ethernet or all Giga-Ethernet).

     2. All switchport commands must be configured on physical interfaces before configuring the logical interface.

     3. Issue the command channel-group x, on the physical interface, will create the logical interface automatically while l inheriting the entire configuration.

Diagram

Configuration

Layer-2 FEC/GEC

SW1:

SW1(config)# interface gigabitEthernet 0/1 SW1(config-if)#switchport mode access SW1(config-if)#switchport nonegotiate SW1(config-if)#switchport trunk encapsulation dot1q SW1(config-if)#switchport mode trunk SW1(config-if)# channel-group 1 mode active Creating a port-channel interface Port-channel 1 SW1(config-if)# exit SW1(config)# interface gigabitEthernet 0/2 SW1(config-if)#switchport mode access SW1(config-if)#switchport nonegotiate SW1(config-if)#switchport trunk encapsulation dot1q SW1(config-if)#switchport mode trunk SW1(config-if)# channel-group 1 mode active SW1(config-if)# exit

SW2:

SW2(config)# interface fastEthernet 0/1 SW2(config-if)#switchport mode access SW2(config-if)#switchport nonegotiate SW2(config-if)#switchport trunk encapsulation dot1q SW2(config-if)#switchport mode trunk SW2(config-if)# channel-group 2 mode active Creating a port-channel interface Port-channel 2 SW2(config-if)# exit SW2(config)# interface fastEthernet 0/2 SW2(config-if)#switchport mode access SW2(config-if)#switchport nonegotiate SW2(config-if)#switchport trunk encapsulation dot1q SW2(config-if)#switchport mode trunk SW2(config-if)# channel-group 2 mode active SW2(config-if)# exit

The nonegotiate ensure that no DTP messages will be exchanged and that the port will be trunk without negotiation.

The channel-group will command will create automatically the logical interface port-channel

The mode active will force the use in LACP protocol

Verification

SW2#show etherchannel 2 summary 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 ------+-------------+-----------+----------------------------------------------- 2      Po2(SU)         LACP      Fa0/1(P)    Fa0/2(P)

In the table we can see which interfaces are members of the port-channel bundle and the port-channel status (S – Layer-2, U – In use) 

SW2#show etherchannel 2 protocol Protocol:  LACP

Shows which protocol is been used in the port-channel Ether-channel, PAgP or LACP 802.3ad

SW2#sh etherchannel 2 detail Group state = L2 Ports: 2   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 = 2           Mode = Active      Gcchange = - Port-channel  = Po2         GC   =   -         Pseudo port-channel = Po2 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     SA      bndl      32768         0x2       0x2     0x1      0x3D  Partner's information:                             LACP port                        Oper    Port     Port Port      Flags   Priority  Dev ID         Age     Key     Number   State Fa0/1     SA      32768     108c.cf99.e980   4s    0x1     0x1      0x3D  Age of the port in the current state: 00d:00h:09m:40s Port: Fa0/2 ------------ Port state    = Up Mstr In-Bndl Channel group = 2           Mode = Active      Gcchange = - Port-channel  = Po2         GC   =   -         Pseudo port-channel = Po2 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     SA      bndl      32768         0x2       0x2     0x2      0x3D  Partner's information:                   LACP port                        Oper    Port     Port Port      Flags   Priority  Dev ID         Age     Key     Number   State Fa0/2     SA      32768     108c.cf99.e980   9s    0x1     0x2      0x3D  Age of the port in the current state: 00d:00h:09m:41s                 Port-channels in the group:                 ---------------------- Port-channel: Po2    (Primary Aggregator) ------------ Age of the Port-channel   = 00d:00h:13m:31s Logical slot/port   = 1/0          Number of ports = 2 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    Active    0   0     00     Fa0/2    Active    0 Time since last port bundled:    00d:00h:09m:43s    Fa0/2

Show more detailed information on the port-channel

Port-channel configuration

SW1 Port-channel 1 configuration:

SW1(config)# interface interface port-channel 1 SW1(config-if)# switchport trunk allowed vlan 1-5 SW1(config-if)# switchport trunk native vlan 5 SW1(config-if)# exit 2:08:13: %SPANTREE-2-RECV_PVID_ERR: Received BPDU with inconsistent peer vlan id 1 on Port-channel2 VLAN5. 02:08:13: %SPANTREE-2-BLOCK_PVID_PEER: Blocking Port-channel2 on VLAN0001. Inconsistent peer vlan. 02:08:13: %SPANTREE-2-BLOCK_PVID_LOCAL: Blocking Port-channel2 on VLAN0005. Inconsistent local vlan. 02:08:14: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan5, changed state to down 02:08:36: %CDP-4-NATIVE_VLAN_MISMATCH: Native VLAN mismatch discovered on FastEthernet0/1 (5), with SW1 GigabitEthernet0/1 (1).

SW2 Port-channel 2 configuration:

SW2(config)# interface interface port-channel 2 SW2(config-if)# switchport trunk allowed vlan 1-5 SW2(config-if)# switchport trunk native vlan 5 SW2(config-if)# exit

We can configure the allowed VLAN’s and native VLAN only on the port-channel, there is no need to configure it on the physical interfaces also.

Note that the native VLAN must be match on the trunk.

Verification

SW1#show interfaces port-channel 1 trunk Port        Mode         Encapsulation  Status        Native vlan Po1         on           802.1q         trunking      5 Port        Vlans allowed on trunk Po1         1-5 Port        Vlans allowed and active in management domain Po1         1-5 Port        Vlans in spanning tree forwarding state and not pruned Po1         1-5 SW1#show interfaces gigabitEthernet 0/1 trunk Port        Mode         Encapsulation  Status        Native vlan Gi0/1       on           802.1q         trunk-inbndl  5                                       (Po1) Port        Vlans allowed on trunk Gi0/1       1-5 Port        Vlans allowed and active in management domain Gi0/1       1-5 Port        Vlans in spanning tree forwarding state and not pruned Gi0/1       1-5