When setting up redundant SEs, the SEs must go in slots 1 and 2. When an SE is active state and the other is in a standby state, the uplink interfaces on the standby SE can be used even if the SE is in a standby state.
Proxy ARP is used when an end station ARPs for a destination device's MAC address that is on a different subnet. A Cisco RP can respond back to the end station with its own MAC address. Proxy ARP is enabled on Cisco RPs by default. If the RP fails, the end station won't discover this unless it reboots or re-ARPs.
IRDP (ICMP), allowing an end station to learn the default gateways that exist. RPs announce themselves every 5 10 minutes and end stations hold this information for up to 30 minutes. The main problem with IRDP is that if the primary RP fails, it might take up to 30 minutes before using a different one.
HSRP is a Cisco-proprietary protocol that provides default gateway redundancy. You can create a total of 255 groups, allowing for load balancing between RPs. A router can belong to several groups. Each group has a virtual IP and MAC address associated with it, which end stations use to send traffic. The MAC address is 0000.0c07.acXX, where XX represents the HSRP group number in hex. The active RP forwards traffic to and from the VLAN. The standby RP monitors the active RP. HSRP states include initial, learning, listening, speaking, standby, and active.
Use the standby ip command to activate HSRP on your RP. Use the standby priority command to change the RP's priority the highest priority becomes the active RP and the second highest becomes the standby RP. The default priority is 100. Use the standby preempt command to enable preemption (disabled by default). HSRP routers send out hellos every 3 seconds, with a hold-down period of 10 seconds. Interface tracking can be used to cause a failover when a tracked interface fails.
VRRP supports Ethernet, VLANs, and MPLS VPNs. There is a master RP and backup RPs. VRRP can use either a virtual IP address or an address from a router to serve as the default gateway address. If a virtual address is used, the RP with the highest priority is elected as master. If a physical IP address is used, the RP with the configured address becomes the master.
