If the terminal is communicating with remote networks, make sure that routes to other networks are set up and the subnet mask is set properly.

For most sites, you need only specify the default gateways described in this section. The terminal maintains current routes in the routing table described in "The IP Routing Table".

Specifying Default Gateways

Default gateways are a reliable way to contact hosts outside the local network. If the terminal cannot find a usable route in the routing table, it contacts the default gateways. You specify the default gateways in the ip-initial-default-gateway-1 and ip-initial-default-gateway-2 parameters (Setup -> Change Setup Parameters -> IP -> Initial Default Gateway 1, Initial Default Gateway 2). These parameters can be saved in NVRAM.

If the host named in the ip-initial-default-gateway-1 parameter is not available, the terminal tries the host listed in ip-initial-default-gateway-2.

If one of the default gateways is 0.0.0.0, the terminal uses the boot host as the default gateway. If both gateways are set to 0.0.0.0, the second is ignored.

The default gateways are automatically placed in the routing table and are the initial entries in the table.

Although you can designate only two gateways using these parameters, you can specify as many additional gateways as you need by entering them into the routing table after the initial configuration file is loaded.

Table 5-26 ip-initial-default-gateway-1 Parameter

NCD terminals maintain an internal routing table that contains current routes to remote hosts and networks. When attempting to reach a host outside the local network, the terminal tries the following methods of finding a route in the order given:

1. A route to the specific host
   

2. A route to the network or subnet the host is on
   

3. The default route, either as specified in ip-initial-default-gateway or obtained via router discovery
   

4. Proxy ARP, if enabled by ip-use-proxy-arp
   

The routing table can contain multiple routes to a single destination. If there is more than one matching route, the terminal uses the route with the greatest preference value.

The routing table changes over time due to normal operation. Routes are placed in the table by:

• Actions of network protocols (proxy ARP, router discovery, and ICMP redirects). See "Finding Routes to Hosts through Proxy ARP" and "Discovering Neighboring Gateways through Router Discovery".
  

• Default gateway parameter settings. These are the first entries in the table after the terminal boots. For more information about the default gateway parameters, see "Specifying Default Gateways".
  

• The system administrator entering routes into the table manually. Manual changes to the routing table take effect immediately.
  

The IP routing table is defined in the ip-routing-table parameter (Change Setup Parameters -> IP -> Routing Table). Routing table entries include read-only values, which you cannot modify, as well as read/write values. The entries in each row of the routing table are defined in Table 5-28.

Entries with the destination 0.0.0.0 are created from the ip-initial-default-gateway-1 and ip-initial-default-gateway-2 parameter settings.

Table 5-28 ip-routing-table Parameter

An example routing table follows:

ip-routing-table = {
    { 0.0.0.0 gateway1.ncd.com -1 dynamic local 42 -1 network }
    { 127.0.0.1 127.0.0.1 0 static local 582 -1 host }
    { 0.0.0.0 eagle.ncd.com -1 dynamic local 42 -1 network }
    { 192.40.157.0 ncdu11.ncd.com 0 static local 39 -1 network }
    }

Proxy ARP resolves routes to hosts for which there are no routes in the IP routing table. It redirects the terminal's request to communicate with a host on another network to the gateway that provides the route to the host. Routes discovered through proxy ARP are automatically placed into the routing table and identified as dynamic routes. The terminal uses hosts specified in the default gateway parameters before resorting to proxy ARP.

To configure the terminal to use proxy ARP, set the ip-use-proxy-arp parameter to "true" (Setup -> Change Setup Parameters -> IP -> Use Proxy Arp). This parameter is saved in NVRAM.

Table 5-29 ip-use-proxy-arp Parameter

Router discovery is an extension to ICMP that enables hosts attached to multicast or broadcast networks to discover the IP addresses of neighboring routers (gateways). If the router discovery daemon is running on your network, you can use this method of discovering routes. The terminal automatically places the routes discovered in the routing table as dynamic routes.

To configure a terminal to use router discovery, make sure the ip-use-router-discovery parameter is set to "true" (the default) (Setup -> Change Setup Parameters -> IP -> Use Router Discovery). This parameter can be saved in NVRAM.

Table 5-30 ip-use-router-discovery Parameter

If the terminal should use router discovery to solicit for routing information at boot time, make sure ip-use-router-solicit is set to "true" (the default) (Setup -> Change Setup Parameters -> IP -> Use Router Solicit). This parameter can be saved in NVRAM.

Table 5-31 ip-use-router-solicit Parameter