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The device to which the default route points is often called the default gateway, and it often carries out other functions such as packet filtering, firewalling, or proxy server operations. The default route in Internet Protocol Version 4 (IPv4) is designated as the zero address, 0.0.0.0 / 0 in CIDR notation. [2]
Static routes are used with and without dynamic Routing protocols and usually share the same routing table as those protocols. [1] Routes require at least two attributes; the destination and the gateway, but may contain additional attributes such as a metric (sometimes called the administrative distance).
The default gateway can be specified by the route command to configure the node's routing table and default route. In a home or small office environment, the default gateway is a device, such as a DSL router or cable router, that connects the local network to the Internet. It serves as the default gateway for all network devices.
The Virtual Router Redundancy Protocol (VRRP) is a computer networking protocol that provides for automatic assignment of available Internet Protocol (IP) routers to participating hosts. This increases the availability and reliability of routing paths via automatic default gateway selections on an IP subnetwork.
To do this, a router needs to search the routing information stored in its routing table. The routing table contains network/next hop associations. These associations tell a router that a particular destination can be optimally reached by sending the packet to a specific router that represents the next hop on the way to the final destination.
When multiple route table entries match, the entry with the longest subnet mask is chosen as it is the most specific one. [2] If there are multiple routes with the same subnet mask, the route with the lowest metric is used. If there are multiple default routes, the metric is also used to determine which to use.
A first hop redundancy protocol (FHRP) is a computer networking protocol which is designed to protect the default gateway used on a subnetwork by allowing two or more routers to provide backup for that address; [1] [2] in the event of failure of an active router, the backup router will take over the address, usually within a few seconds.
Here is very important role of L1/L2 router - if it is connected to L2 router in another area, then it sets ATT (ATTached bit) in its L1 LSP. L1 routers which receive this LSP (with ATT bit) add default route to originator of this LSP. This is different from OSPF, where ABR generates default route to stub area routers and sends it via LSA 3.