How the appliance handles routing

The appliance does not function as a router

Although the appliance can have multiple network interfaces, it does not function as a router; that is, the appliance does not route packets between its interfaces on behalf of other network hosts.

How the appliance routes its own packets

For routing its own packets, as well as dynamic routes, the appliance relies on the default route and static routes. Normally, the appliance learns explicit routes through Internet Control Message Protocol (ICMP) redirect messages received from the default router; you do not need to enter static routes in the appliance's routing table.

Configuration considerations

You need to enter static routes in the appliance's routing table only if your default gateway is not aware of some addresses and you are not able to route packets to those addresses through RIP or IRDP.

Management of network routing tables

The appliance uses the routed daemon to manage the network routing tables. Routed is a simple routing daemon that is enabled at boot time. Routed uses the Routing Information Protocol (RIP), which listens for packets being exchanged between routers on the network and solicits multicast router discovery Internet Control Message Protocol (ICMP) messages. The appliance uses RIP response packets to update its routing tables. The routing tables are updated with gateways that are currently recognized on the network, or with gateways that advertise a better metric than at least one of the gateways currently listed in the routing tables.

Configuration considerations

RIP is enabled by default. Disabling RIP stops the appliance from listening for RIP response packets, and information in the routing table remains static.

About Route Discovery

The Internet Router Discovery Protocol (IRDP), which is an extension of ICMP, enables hosts attached to multicast or broadcast networks to discover the IP addresses of neighboring routers. When the Route Discovery feature is enabled, the appliance listens to Router Discovery messages, thereby eliminating the need to manually configure the default gateway. If the default router goes down, IRDP informs the appliance about alternative routers, ensuring that the appliance maintains its connection to the Internet. Only routers that support IRDP can be discovered through the Route Discovery feature.

Configuration considerations

Route Discovery is disabled by default. If your routers are not configured to support IRDP, do not enable this option.