리눅스 서버 머신에 랜카드를 3개 꽂은 뒤......
 eth0
eth1 : 192.168.10.1
eht2 : 192.168.11.1
 요렇게 아이피를 정해놓구요...
 랜카드랑 연결된 컴 마다가 각각 192.168.10.2 , 192.168.11.2 내부아이피를 지정했습니다.
 첫번째 컴퓨터 즉 eth1과 연결된 컴은 인터넷 사용이 잘 됩니다.
 그러나..
 두번째 컴퓨터 즉 eth2와 연결된 컴터에서는 내부로는 ping이 다 쏴지는데,
 외부로는 ping이 나가질 않네요...
 ---------------------------------------------------------------
 /etc/sysconfig/network 내용입니다.
 NETWORKING=yes
HOSTNAME=linux.keinlee.net
DOMAINNAME=keinlee.net
FORWARD_IPV4=yes
GATEWAYDEV=eth1
GATEWAY=192.168.10.1
GATEWAYDEV=eht2
GATEWAY=192.168.11.1
 ---------------------------------------------------------------
 이건 route결과입니다.
 Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
211.245.201.0 * 255.255.255.0 U 0 0 0 eth0
192.168.11.0 * 255.255.255.0 U 0 0 0 eth2
192.168.10.0 * 255.255.255.0 U 0 0 0 eth1
127.0.0.0 * 255.0.0.0 U 0 0 0 lo
default 211.245.201.1 0.0.0.0 UG 0 0 0 eth0
 ---------------------------------------------------------------
 /etc/sysconfig/network-scripts/ifcfg-eth2의 내용입니다.
 DEVICE=eth2
IPADDR=192.168.11.1
NETMASK=255.255.255.0
BRODCAST=12.168.11.255
ONBOOT=yes
BOOTPROTO=none
 ---------------------------------------------------------------
 ifconfig 내용입니다.
 eth0 Link encap:Ethernet HWaddr 00:02:2A:DA:07:3D
inet addr:211.245.201.112 Bcast:211.245.201.255 Mask:255.255.255.0
UP BROADCAST NOTRAILERS RUNNING MTU:1500 Metric:1
RX packets:10286 errors:0 dropped:0 overruns:0 frame:0
TX packets:6808 errors:0 dropped:0 overruns:0 carrier:0
collisions:0
RX bytes:5306207 (5.0 Mb) TX bytes:1043310 (1018.8 Kb)
 eth1 Link encap:Ethernet HWaddr 00:02:2A:D5:43:DF
inet addr:192.168.10.1 Bcast:192.168.10.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:8109 errors:0 dropped:0 overruns:0 frame:0
TX packets:8493 errors:0 dropped:0 overruns:0 carrier:0
collisions:554
RX bytes:1128283 (1.0 Mb) TX bytes:5229693 (4.9 Mb)
 eth2 Link encap:Ethernet HWaddr 00:02:2A:DC:04:5B
inet addr:192.168.11.1 Bcast:192.168.11.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:436 errors:0 dropped:0 overruns:0 frame:0
TX packets:299 errors:0 dropped:0 overruns:0 carrier:0
collisions:0
RX bytes:47492 (46.3 Kb) TX bytes:33657 (32.8 Kb)
 lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:34 errors:0 dropped:0 overruns:0 frame:0
TX packets:34 errors:0 dropped:0 overruns:0 carrier:0
collisions:0
RX bytes:2940 (2.8 Kb) TX bytes:2940 (2.8 Kb)
 ---------------------------------------------------------------
 /etc/rc.d/rc.local 마지막 부분에 넣은 내용입니다.
 ipchains -A forward -s 192.168.10.0/24 -d 0.0.0.0/0 -j MASQ
ipchains -A forward -s 192.168.11.0/24 -d 0.0.0.0/0 -j MASQ
  보시고 빠진부분이나 추가해야할 부분 있으면 가르쳐주세요.....
 좋은 가르침 부탁합니다.