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When enabling DHCP, the DHCP relay is also enabled automatically. Relay cannot be disabled
without disabling DHCP.
3.3.3 VRRP: Virtual Router Redundancy Protocol
VRRP (Virtual Router Redundancy Protocol) adds a set of routers that can undertake gateway
function into a backup group to form a virtual router. The election mechanism of VRRP will decide
which router to undertake the forwarding task and the host in LAN is only required to configure
the default gateway for the virtual router.
VRRP will bring together a set of routers in LAN. It consists of multiple routers and is similar to a
virtual router in respect of function. According to the VLAN interface IP of different network
segments, it can be virtualized into multiple virtual routers. Each virtual router has an ID number
and up to 255 can be virtualized.
VRRP has the following characteristics:
Virtual router has an IP address, known as the Virtual IP address. For the host in
LAN, it is only required to know the IP address of virtual router, and set it as the
address of the next hop of the default route.
Host in the network communicates with the external network through this virtual
router.
A router will be selected from the set of routers based on priority to undertake the
gateway function. Other routers will be used as backup routers to perform the
duties of gateway for the gateway router in case of fault of gateway router, thus to
guarantee uninterrupted communication between the host and external network
Monitor interface function of VRRP better expands backup function: the backup function can be
offered when interface of a certain router has fault or other interfaces of the router are
unavailable.
When interface connected with the uplink is at the state of Down or Removed, the router actively
reduces its priority so that the priority of other routers in the backup group is higher and thus the
