あまりにもニッチな記事なので、特に解説はいたしません。
ヤマハのルーターRTX1100を使って、LAN内にある別のLANにぶらがっているパソコン（下図のPC1、PC2）から、インターリンクのマイIPサービス（PPTP）を使って、インターネット側に接続元を固定IPとする接続するための設定をしてみました。
コンフィグは以下のとおりです。
# show config
# RTX1100 Rev.8.03.92 (Thu Feb 16 20:50:25 2012)
# Reporting Date: Jan 2 08:22:03
ip route default gateway tunnel 1
ip route 203.141.xxx.xxx gateway dhcp lan2
ip lan1 address 192.168.2.1/24
ip lan2 address dhcp
pp select 1
pp bind tunnel1
pp keepalive use lcp-echo
pp keepalive interval 10
pp auth accept chap
pp auth myname username password
ppp ccp type mppe-any
ppp ipv6cp use off
ip pp mtu 1280
ip pp nat descriptor 1
pptp service type client
pp enable 1
tunnel select 1
tunnel encapsulation pptp
tunnel endpoint address 203.141.xxx.xxx
pptp tunnel disconnect time off
pptp keepalive use on
ip tunnel nat descriptor 1
tunnel enable 1
nat descriptor type 1 masquerade
dhcp service server
dhcp server rfc2131 compliant except remain-silent
dhcp scope 1 192.168.2.11-192.168.2.20/24
dns server 203.141.128.xxx 203.141.128.xxx
pptp service on
結果。
# show status pptp
------------------- PPTP INFORMATION -------------------
Number of control table using
Tunnel Control: 1, Call Control: 1, GRE Control: 1
TUNNEL[01] Information
TCP status: established
PPTP Call status: established
PPTP Service type: client
PNS status: established
Remote IP Address: 203.141.xxx.xxx
Local IP Address: 0.0.0.0
GRE status: open
Transmitted: 108 packets [7270 octets]
Received: 110 packets [11761 octets]
Transmit left: 0 packet
Transmitted ack number: 110 times
Transmit ready timeout: 218 times
Received ack number: 19 times
Received invalid sequence: 0 packet
Received delayed sequence: 0 packet
Received invalid ack: 0 packet
Received delayed ack: 0 packet
Received out of sequence: 0 packet
Received no data packet: 0 packet
MPPE Information
Rx key changed: 0
Tx key changed: 0
synchronized: 1
received delay: 0 time
lost detected: 0 time
reset condition: 0 time
reset done: 0 time
ぐっどらっこ。