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Configuring Routing (Accessing Remote Networks)

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, the terminal uses the boot host as the default gateway. If both gateways are set to, 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
Possible Values
default The gateway is the boot host.
IP address or hostname A default gateway.

Table 5-27 ip-initial-default-gateway-2 Parameter
Possible Values
default The gateway is the boot host.
IP address or hostname A default gateway.

The IP Routing Table

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:

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 are created from the ip-initial-default-gateway-1 and ip-initial-default-gateway-2 parameter settings.

Table 5-28 ip-routing-table Parameter
Table Entry
Possible Values
Field Type
destination default read/write The entry is one of the default gateways.
IP address or hostname Address of the host network or name of the host.
gateway default read/write
IP address or hostname The IP address of the next hop on this route.

If the route is bound to an interface that is realized through a broadcast medium, this field contains the agent's IP address on the interface.

preference default 0 read/write
0 The midpoint of the preference range.
integer Determines which route is preferred when there are multiple routes to a destination. Router discovery messages convey this information dynamically; otherwise, you can configure it statically. The terminal tries higher-numbered routes first.
Range: -2147483648 to 2147483647.
type default static read/write
static The system administrator created the route and it cannot be deleted or marked unusable.
dynamic The network discovered the route (by the proxy ARP, ICMP, or router discovery protocols) and it can be deleted or marked unusable if the terminal detects failures when using the route.
creation-method default snmp read/write
snmp SNMP set the route.
icmp ICMP set the route.
local The system administrator created the route.
proxy-arp Proxy ARP created the route.
birth default 0 read-only
integer Amount of time (in seconds) after booting that the route was created.
time-to-live -1 The route should not be automatically deleted. read/write
integer How long (in seconds) before the route is deleted. This information is conveyed in router discovery messages. Range: 1 - 2147483647
destination-type default network read/write
network The destination is a network. Most routes are network routes.
host The destination is a host. Proxy ARP routes and the routes used for SLIP (Serial Line Internet Protocol) connections are host routes.
route-mask hexadecimal number A hexadecimal value indicating the bits in the destination address used to determine the route. The mask is logically AND-ed with the destination address before being compared to the value in the gateway field. This field is used by SNMP (Simple Network Management Protocol). read-only

An example routing table follows:

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

Finding Routes to Hosts through Proxy ARP

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
Possible Values
default false
false The terminal does not use proxy ARP to locate gateways.
true The terminal uses proxy ARP to locate gateways.

Discovering Neighboring Gateways through Router Discovery

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
Possible Values
default true
true The terminal modifies its IP routing table with information received from router discovery messages.
false The terminal does not modify its routing table with information received from router discovery messages.

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
Possible Values
default true
true The terminal solicits for routing information.
false The terminal does not solicit for routing information.

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