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Router configuration rules may contain static routes. A static route minimally has a destination address, a prefix length or subnet mask, and a definition where to send packets for the route. That definition can refer to a local interface on the router, or a next-hop address that could be on the far end of a subnet to which the router is connected.
In order to achieve a successful transfer of data, the algorithm uses a routing table to select a next-hop router as the next destination for a datagram. The IP address of the selected router is known as the next-hop address. [1] The IP forwarding algorithm states: [2] Given a destination IP address, D, and network prefix, N:
ISPs (using automated tools) then generate router configuration files that match their business and technical policies. RFC2622 describes RPSL, and replaced RIPE-181. RFC2650 provides a reference tutorial to using RPSL in practice to support IPv6 routing policies.
Static routing may have the following uses: When using static address configuration (in the absence of DHCP or Router Advertisements) it can be used to provide a default route, forming a special case of the longest prefix match as it has a prefix length of zero and therefore always matches, and always matches last.
The router which first prefixes the MPLS header to a packet is an ingress router. The last router in an LSP, which pops the label from the packet, is called an egress router. Routers in between, which need only swap labels, are called transit routers or label switch routers (LSRs).
Using this map, each router independently determines the least-cost path from itself to every other node using a standard shortest paths algorithm such as Dijkstra's algorithm. The result is a tree graph rooted at the current node, such that the path through the tree from the root to any other node is the least-cost path to that node.
In the typical case of a home network, for example, the home router uses DHCPv6 to request a network prefix from the ISP's DHCPv6 server. Once assigned, the ISP routes this network to the customer's home router and the home router starts advertising the new address space to hosts on the network, either via SLAAC or using DHCPv6.
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.