
Configuring IP Services
3-28 114065 Rev. A
In Figure 3-4, the router wants to send a packet to Host C but knows only Host C’s
IP address. The router uses ARP to determine Host C’s physical address, as
follows:
1. The router broadcasts a special packet, called an ARP request, that asks IP
address 140.250.200.4 to respond with its physical address.
2. All network hosts receive the broadcast request.
3. Only Host C responds with its hardware address.
The router maps Host C’s IP address (140.250.200.4) to its physical address
(00 00 A2 00 10 40) and saves the results in an address-resolution cache for future
use.
You can use Site Manager to
• Control how ARP acts in relation to IP’s forwarding state.
• Control whether IP drops and logs an invalid ARP source address or simply
drops the request.
• Control whether IP drops or accepts ARP requests in which the source and
destination addresses are located in different networks or subnetworks. This
parameter allows Proxy ARP to generate replies when the source and
destination networks in the ARP request differ.
Note: It is possible for the router to send out ARP requests even if ARP, which
is a dynamically loaded module, is not currently loaded on the router. It is the
responsibility of the network administrator to ensure that ARP is loaded
correctly on a slot. To do this through Site Manager, select Events Manager >
Options > Filters; then select LOADER and Debug, and do a File > Get
Current Log File. Verify that ARP is loaded on a slot by locating the following
message in the log:
#xx:01/01/95 10:10:55.00 DEBUG SLOT x LOADER CODE:33
Loader service completed for ARP.EXE 0xxxxxxxxx
Site Manager: ARP Forwarding parameter: page A-40
Site Manager: Nonlocal ARP Source parameter: page A-40
Site Manager: Nonlocal ARP Destination parameter: page A-41
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