IP routes

Default gateways

Multiple default gateways are supported for routing IP traffic. When connected to multiple IP networks, add a default gateway for each network to which the server is connected. This configuration lets the server direct traffic through the appropriate default gateway by matching source IP addresses specified in outgoing packets with the gateway on the same subnet.

With multiple default gateways, the server routes IP traffic logically, reducing the need to specify static routes for every network that connects with a particular server.

Static routes

Static routing gives a fixed path for data in a network. When a server on a network is connected to additional networks through a router, communication between that server and the remote networks can be enabled by specifying a static route to each network.

Static routes are set up in a routing table. Each entry in the table consists of a destination network address, a gateway address, and a subnet mask. Entries for static routes in the server’s routing table are persistent, meaning that if a server is restarted, the routing table preserves the static routing entries.

Dynamic routes

Internet Control Message Protocol (ICMP) redirects and the Routing Information Protocol (RIP) are used to dynamically add routes to its route table.

ICMP redirects are a mechanism for routers to convey routing information back to the server. When one router detects that another router offers a better route to a destination, it sends the server a redirect that temporarily overrides the server's routing table. Being router-based, dynamic redirects do not require any configuration, but they can be viewed in the routing table.

The server supports ICMP router discovery, which lets the server discover the addresses of routers. ICMP routers periodically multicast their addresses; when the server receives these multicasts, it incorporates the routers into its routing table.

RIP lets the server automatically discover routes and then update routes in the routing table based on updates provided by other network devices.

The server stores dynamic host routes in its route cache for 10 minutes. When the time has elapsed, packets to a selected destination use the route specified in the routing table until the server receives another ICMP redirect.