Perle Systems PERLE P850 - Manual (Page 50)

Applications
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remote site profile settings. The WAN IPX network number is defined
with the IPX Net option in the remote site profile settings.
Unnumbered Links
An unnumbered link does not use network addressing on the WAN
link. The WAN connection is roughly equivalent to an internal
connection with each of the two end point routers operating as half of
a complete router that is connected between the two endpoint LANs.
When an IPCP link is set to unnumbered, the only configuration
option applicable is Peer IP Address. The peer IP address in this case
is the IP address of the remote PPP router, that is the IP address of its
LAN connection. If the peer IP address is not specified, the P850
router will attempt to determine it when negotiating the IPCP
connection.
When an IPXCP link is set to unnumbered, no addressing
configuration is required. All of the IPX settings are negotiated during
the IPXCP connection.