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Network Configuration—PPPOption-dedicated-ddial-interactiveDescriptionPPP assumes the link is always connected and that there is noneed to establish the physical link. This mode is mostly used forPPPoE/PPPoA.Dial-on-demand mode (just like –auto) with auto redialing, whenthe line is dropped.Enters the interactive prompt mode, where the user can manuallycontrol the PPP connection establishment.To establish a PPP connection to myisp in the previous example, you may runppp(8) as follows:# ppp -ddial myispLoading /lib/libalias_cuseeme.soLoading /lib/libalias_ftp.soLoading /lib/libalias_irc.soLoading /lib/libalias_nbt.soLoading /lib/libalias_pptp.soLoading /lib/libalias_skinny.soLoading /lib/libalias_smedia.soWorking in ddial modeUsing interface: tun0This runs the user PPP daemon in the background (note -ddial option), andestablishes a PPP connection as configured under myisp tag in the /etc/ppp/ppp.conf file. It also tries to re-establish the connection if it drops.PPP also has built-in support for Network Address Translation (NAT) withoutinvolving third-party applications. This can be achieved by using the -nat option inthe command line.For example, to enable NAT in the previous example, you may use thefollowing command:# ppp –ddial –nat myispBy enabling the NAT function, PPP will masquerade all packets with private IPaddresses (as per RFC 1918) as the source address.A typical scenario of using NAT is to set up a LAN interface with private IPaddresses (for example 172.16.10.0/24) and use it as the default gateway of yournetwork. So when clients with the source IP address within the 172.16.10.0/24network send their packets towards Internet using their gateway, PPP daemon willautomatically pick up and translate the traffic using its established PPP interface. Soyou do not need to set up NAT using the traditional natd and ipfw combination.[ 148 ]