Once a PPP link is established, routes must be established that carry traffic
between the link and local MachTen application programs or across local
PPP Default Route
The simplest method of establishing a route to the PPP link is to use the
defaultroute /usr/libexec/pppd parameter. See /etc/pppclient
for information about specifying the defaultroute parameter. This parameter
causes a pppd to make the system-wide default route from the newly established
PPP link and it's associated internet addresses. If a link was established
with a local internet address 188.8.131.52 and a remote internet address of
184.108.40.206 a route would be established to 220.127.116.11 using interface 18.104.22.168.
This route would be made the system-wide default route which would be used
in the event that no other route in the routing table matched the destination
The system routes can be displayed with the netstat
Destination Gateway Flags Refs Use Interface
default 22.214.171.124 UG 0 0 ie0
127.0.0.1 127.0.0.1 UH 1 0 lo0
192.83.246 126.96.36.199 U 1 75 ie0
PPP Subnet Masks
In order to properly establish a route, many times, a subnet mask must be
used to cause parts of an internet domain to be routed to an interface and
other parts of an internet domain to be routed elsewhere. To support this
feature, the /usr/libexec/pppd has a netmask parameter which is used in
combination with any derived local internet addresses to segregate parts
of a single internet domain into different logical subnet routes. The netmask
parameter is specified by a netmask identifier followed by a numerical mask.
This is an example of a netmask specification:
When a packet has a destination address that does not exactly match one
of the local host addresses, the PPP link is examined as a possible destination
for the packet. To determine if the PPP link qualifies as the "best"
destination, the PPP link internet address is logically anded with the numerical
subnetmask specified by the subnetmask parameter. The destination address
from the packet is also logically anded with the subnetmask from the parameter.
If the two logically anded results match, the PPP link is used to transport
the packet a step closer to it's destination.
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