Two ideas keep a network running when hardware fails: a backup default gateway (HSRP) and several physical links bundled into one logical link (EtherChannel).

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HSRP: a shared gateway address

Two routers share a virtual IP. Hosts use that address as their gateway, and the standby router takes over if the active one fails.

R1(config)# interface g0/1
R1(config-if)# ip address 192.168.10.2 255.255.255.0
R1(config-if)# standby 1 ip 192.168.10.1
R1(config-if)# standby 1 priority 110
R1(config-if)# standby 1 preempt

On R2 use its own address (for example 192.168.10.3) with the same standby 1 ip and the default priority of 100. The higher priority becomes active, and preempt lets R1 take the role back after it recovers.

show standby brief

EtherChannel: bundle links with LACP

Switch(config)# interface range g0/1-2
Switch(config-if-range)# channel-group 1 mode active
Switch(config)# interface port-channel 1
Switch(config-if)# switchport mode trunk
show etherchannel summary
  • Use active on at least one side (active/active or active/passive) for LACP.
  • Do not mix LACP with PAgP on the same bundle.
  • Every member port needs the same speed, duplex and VLAN settings.

Test it. Shut down one member link or the active router in Packet Tracer and watch the traffic keep flowing.