3.0 CCNA - IP Connectivity
3.5 First hop redundancy protocol
The purpose of first hop redundancy protocols is to provide redundancy and high availability in the first hop IP network, which is the network segment between the end-user device and the default gateway. The default gateway is responsible for forwarding IP packets from the end-user device to the rest of the network.
In a traditional IP network, if the default gateway fails, the end-user device will not be able to reach any other hosts in the network. First hop redundancy protocols address this issue by providing redundancy and failover capabilities at the first hop of the IP network.
There are several first hop redundancy protocols, including:
1. Hot Standby Router Protocol (HSRP): a proprietary redundancy protocol developed by Cisco Systems that provides redundancy for IP networks.
2. Virtual Router Redundancy Protocol (VRRP): an open standard redundancy protocol that provides redundancy for IP networks.
3. Gateway Load Balancing Protocol (GLBP): a proprietary redundancy protocol developed by Cisco Systems that provides load balancing and redundancy for IP networks.
These protocols work by creating virtual IP addresses and virtual default gateways that are shared among multiple routers. When one of the routers fails, the others take over the virtual IP addresses and virtual default gateway IP addresses, ensuring that the end-user device always has a functioning default gateway to reach the rest of the network.
Example configurations:
1. Hot Standby Router Protocol (HSRP) on a Cisco router:
interface FastEthernet0/0 ip address 192.168.1.1 255.255.255.0 standby version 2 standby 1 ip 192.168.1.254 standby 1 priority 110 standby 1 preempt
2. Virtual Router Redundancy Protocol (VRRP) on a Cisco router:
interface FastEthernet0/0 ip address 192.168.1.1 255.255.255.0 vrrp 1 ip 192.168.1.254 vrrp 1 priority 110 vrrp 1 preempt
3. Gateway Load Balancing Protocol (GLBP) on a Cisco router:
interface FastEthernet0/0 ip address 192.168.1.1 255.255.255.0 glbp 1 ip 192.168.1.254 glbp 1 priority 110 glbp 1 preempt glbp 1 load-balancing round-robin