So will configure “standby 50 ip 10.10.50.250” command on DS01 & DS02 vlan 50 interface. If you haven’t specify a group number it will assume group number as 0. Therefore virtual MAC address should be 0000.0c07.0032 (where 50 is in hex 32). In this example will configure HSRP Group no 50 ( a value between 0 -255). Minimum configuration wise you need to configure “standby ip ” in order to activate HSRP on an interface. Virtual IP address as the gateway IP address Redirect Configure sending of ICMP Redirect messages with an HSRP Preempt Overthrow lower priority Active routers Mac-refresh Refresh MAC cache on switch by periodically sending packet Ip Enable HSRP IPv4 and set the virtual IP address All configurable options shown below (highlighted few commonly configured features). To configure the HSRP parameters on this interface you have to use command syntax “ standby “. When we selecting HSRP Active, it is always good idea to select spanning tree root for that VLAN select as HSRP active for that vlan. Below shows a typical topology which we are going to see how we configure HSRP. Hosts on the adjoining LAN segment use the normal Address Resolution Protocol (ARP) process in order to resolve the associated MAC addresses.Įven though HSRP group can be consist of multiple layer 3 devices, in typical enterprise environment distribution block (two aggregation switches) is configured with HSRP to provide gateway redundancy to all access layer VLANs. For example, HSRP group 1 uses the HSRP virtual MAC address of 01. Virtual MAC address that is composed of ** where ** is the HSRP group number in hexadecimal, based on the respective interface. This use of source addressing is necessary so that HSRP routers can correctly identify each other.
The standby router sources hellos from its configured IP address and the burned-in MAC address (BIA). The active router sources hello packets from its configured IP address and the HSRP virtual MAC address. IP multicast address 224.0.0.2 is a reserved multicast address that is used to communicate to all routers. These packets are sent to the destination IP multicast address 224.0.0.2 on User Datagram Protocol (UDP) port 1985. Routers that run HSRP communicate HSRP information between each other through HSRP hello packets. Although an arbitrary number of routers may run HSRP, only the active router forwards the packets that are sent to the virtual router IP address. If the active router fails, the standby assumes the packet forwarding duties. Another router is elected as the standby router. This router is known as the active router. There is no RFC for version 2 of the protocol.Hot Standby Routing Protocol (HSRP) is Cisco standard of providing redundancy for IP host configured in a LAN network with default gateway address.It enables a set of router interfaces to work together to present the appearance of a single virtual router or default gateway to the hosts on a LAN.Ī single router that is elected from the group is responsible for the forwarding of the packets that hosts send to the virtual router.
It is not compatible with version 1 HSRP. Version 2 of the protocol introduces stability, scalability and diagnostic improvements. If the link of the primary router goes down, the backup router will take over the primary functionality and thus retain connectivity to the gateway. This can be useful for dual branch routers each with a single link back to the gateway. HSRP has the ability to trigger a failover if one or more interfaces on the router go down. HSRP is not a routing protocol as it does not advertise IP routes or affect the routing table in any way. In the virtual MAC address, Xs represent the group ID in hex. If the primary router should fail, the router with the next-highest priority would take over the gateway IP address and answer ARP requests with the same MAC address, thus achieving transparent default gateway failover. The primary router with the highest configured priority will act as a virtual router with a pre-defined gateway IP address and will respond to the ARP or ND request from machines connected to the LAN with a virtual MAC address.