Dell PowerConnect 8100 CLI Reference Guide - Page 1379

58 Virtual Router Redundancy Protocol Commands An end station running IP needs to know the address of its first hop router. While some network administrators choose to install dynamic router discovery protocols such as DHCP, others prefer to statically allocate router addresses. If the router identified by such a statically allocated address goes down, the end station loses connectivity. The Virtual Router Redundancy Protocol (VRRP) is designed to provide backup for the failing router without requiring any action on the part of the end station. It is based on the concept of having more than one router recognize the same IP address. One of the routers is elected the master router and handles all traffic sent to the specified virtual router IP address. If the master router fails, one of the backup routers is elected in its place and starts handling traffic sent to the address. This change is transparent to end stations. VRRP increases the availability of the default path without requiring configuration of dynamic routing or router discovery protocols on every end station. Multiple virtual routers can be defined on a single router interface. Pingable VRRP Interface RFC 3768 specifies that a router may only accept IP packets sent to the virtual router's IP address if the router is the address owner. In practice, this restriction makes it more difficult to troubleshoot network connectivity problems. When a host cannot communicate, it is common to ping (send an ICMP Echo Request) the host's default gateway to determine whether the problem is in the first hop of the path to the destination. When the default gateway is a virtual router that does not respond to pings, the operator cannot use this troubleshooting technique. Because of this, it has been common for VRRP implementations to respond to pings, in spite of the prohibition in the RFC. The IETF has recognized the issue, and a draft revision of the VRRP Virtual Router Redundancy Protocol Commands 1379