DNAT and MASQUERADE

[Erez D]

hello.

I have an iptables question

i have the following

ext_ip -> NAT1 -> linux firewall-> network -> computer1:eth0 .. computer99

i have no control over NAT1.
computer1 also can reach the internet via eth1.

linux firewall redirects incoming port 7777 from ext_ip to computer1
however i need coputer2 .. computer99 to connect to ext_ip:7777 and also
reach computer1

so first i did a NAT rule in linux firewall to redirect all packets from
internal to ext_ip:7777  to computer1. and did an 'ifconfig eth0:1 $ext_ip
up' on computer1.
this works. however it causes computer1 not to be able to access real
ext_ip via eth1 which is connected to the internet as well

so i though of both doing DNAT and MASQ, which will do the same but will
not require assiging ext_ip to computer1.
howerver i do not know how to do that

anyone ?
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