EtherChannel with LACP Configuration

Configure FastEthernet 0/1 and 0/2 as an EtherChannel in trunk mode:

interface range f0/1-2
  shutdown
  channel-group <identifier> mode active
  !channel-group <identifier> mode desirable
  no shutdown

interface port-channel <identifier>
  switchport mode trunk
  switchport trunk allowed vlan 1,2,20

Verifying EtherChannel

show interfaces port-channel <identifier>
show etherchannel summary
show etherchannel port-channel
show interfaces etherchannel

Troubleshooting EtherChannel

show etherchannel summary
show run | begin interface port-channel

HSRP Configuration Commands

Complete the following steps to configure HSRP in interface command mode:

Step 1. Configure HSRP version 2.

standby version 2

Step 2. Configure the virtual IP address for the group.

standby [group-num; default=0] <ip-address>

Step 3. Configure the priority for the desired active router to be greater than 100.

standby [group-num] priority [priority-value; default=100]

HSRP priority can be used to determine the active router. The router with the highest HSRP priority will become the active router. By default, the HSRP priority is 100. If the priorities are equal, the router with the numerically highest IPv4 address is elected as the active router.
By default, after a router becomes the active router, it will remain the active router even if another router comes online with a higher HSRP priority.

Step 4. Configure the active router to preempt the standby router in cases where the active router comes online after the standby router.

Preemption is the ability of an HSRP router to trigger the re-election process. With preemption enabled, a router that comes online with a higher HSRP priority will assume the role of the active router.

standby [group-num] preempt

Example:

R1 (Active Router):

interface g0/1
  ip address 172.16.10.2 255.255.255.0
  standby version 2
  standby 1 ip 172.16.10.1
  standby 1 priority 150
  standby 1 preempt
  no shut

R2 (Standby Router):

interface g0/1
  ip address 172.16.10.3 255.255.255.0
  standby version 2
  standby 1 ip 172.16.10.1
  no shut

Verify/Debug HSRP State

show standby
show standby brief

debug standby errors
debug standby events
debug standby packets
debug standby terse