демон протокола точка-точка (Point-to-Point Protocol Daemon)
ROUTING
When IPCP negotiation is completed successfully, pppd will inform
the kernel of the local and remote IP addresses for the ppp
interface. This is sufficient to create a host route to the
remote end of the link, which will enable the peers to exchange
IP packets. Communication with other machines generally requires
further modification to routing tables and/or ARP (Address
Resolution Protocol) tables. In most cases the defaultroute
and/or proxyarp options are sufficient for this, but in some
cases further intervention is required. The /etc/ppp/ip-up
script can be used for this.
Sometimes it is desirable to add a default route through the
remote host, as in the case of a machine whose only connection to
the Internet is through the ppp interface. The defaultroute
option causes pppd to create such a default route when IPCP comes
up, and delete it when the link is terminated.
In some cases it is desirable to use proxy ARP, for example on a
server machine connected to a LAN, in order to allow other hosts
to communicate with the remote host. The proxyarp option causes
pppd to look for a network interface on the same subnet as the
remote host (an interface supporting broadcast and ARP, which is
up and not a point-to-point or loopback interface). If found,
pppd creates a permanent, published ARP entry with the IP address
of the remote host and the hardware address of the network
interface found.
When the demand option is used, the interface IP addresses have
already been set at the point when IPCP comes up. If pppd has
not been able to negotiate the same addresses that it used to
configure the interface (for example when the peer is an ISP that
uses dynamic IP address assignment), pppd has to change the
interface IP addresses to the negotiated addresses. This may
disrupt existing connections, and the use of demand dialling with
peers that do dynamic IP address assignment is not recommended.
