Re: Squid as default gateway in proxy mode.



Hello,

Muhammad Yousuf Khan <sirtcp@xxxxxxxxx> wrote:

now the problem part is i want to ping outside host to verify the
connectivity of internet for that all the time i have to open the SSH
the console and ping. but what i want is, i should also ping it from
host computers as well. however i don't want to NAT all the traffic
coming from inside and going outside. rather what i want is just to
NAT only ICMP Echo Rep and Req so that i can at least ping outside
host

As Joe wrote, this is not the right way to do things. See below.

with out SSH the Squid console. which is very bothering.
My network diagram is very simple

<Squid
Box>--------eth0(192.18.30.2)----------------------<192.168.30.1-ISP
Router>
I
I
eth1(192.168.1.1)
I
I
(local network 192.168.1.0/24)


And why i am using Squid as a Gateway because i just want to minimize
unwanted nods that needs to be monitor all the time and batter
control over traffic with IPtables firewall. i am using this line to
NAT very specific ports to allow certain facilities like Email ,
Remote desktop and stuff. and this is working for me.

iptables -t nat -A POSTROUTING -p TCP --dport 110 -j MASQUERADE

This is not the right way to do things. NAT is not intended for
filtering. By not masquerading outgoing traffic, you just let packets go
out with their original source address instead of dropping them. You
just rely on the ISP router not knowing how to handle the original
source address. This is wrong.

The right way is to only accept specific through your router, and then
NAT all traffic that was allowed to go out. Ok, it is a bit more
complicated.

iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE
iptables -t filter -P FORWARD DROP
iptables -t filter -A FORWARD -m state --state ESTABLISHED,RELATED \
-j ACCEPT
iptables -t filter -A FORWARD -o eth0 -m state --state NEW \
-p tcp --dport 110 -j ACCEPT

now i am stuck on allowing the ping traffic. please help

iptables -t filter -A FORWARD -0 eth0 -p icmp --icmp-type echo-request \
-j ACCEPT

Joe wrote :
only TCP and UDP have 'ports'

No. ICMP does not have ports, but other protocols such as SCTP and DCCP
have ports too.


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