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I need to complete an exercise with iptables on a network (docker containers) configured as follows:

  1. A router host with 2 network interfaces (eth0 <- public 10.9.0.0/24; eth1 <- lan 192.168.60.0/24; the router is the x.x.x.254 on both networks) and an SSH server on default port 22;
  2. A jumpbox host in lan with IP 192.168.60.10, with SSH and TELNET on default ports 22 and 23;
  3. An admin host in public with IP 10.9.0.2.

One of the requests made to us is the forwarding/masquerade of the SSH (on port 2222) and TELNET services of the jumbox host via the router to the admin host.
The problem is that I can't redirect these ports, the connection remains on perpetual hold (I think because the return packets are not configured correctly).
Currently my configuration is as follows (see ADMIN'S RULES):

#!/bin/bash

# Reset IPv4 rules
iptables -t filter -F
iptables -t filter -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X

# Set default policies for chains
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT

# Allow loopback traffic
iptables -A INPUT -i lo -j ACCEPT

# Allow traffic for ongoing connections
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ACCEPT


# ====================== #
#  NAT INTERNAL NETWORK  #
# ====================== #

# Masquerade internal network hosts
iptables -t nat -A POSTROUTING -s 192.168.60.0/24 -o eth0 -j MASQUERADE

# Forward internal network requests to external network
iptables -A FORWARD -i eth1 -o eth0 -j ACCEPT


# =============== #
#  ADMIN'S RULES  #
# =============== #

# Allow 'admin' connection to 'jumpbox' SSH (on 2222 port)
iptables -t nat -A POSTROUTING -s 192.168.60.10 -p tcp --sport 22   -j SNAT --to 10.9.0.254:2222
iptables -t nat -A PREROUTING  -s 10.9.0.2      -p tcp --dport 2222 -j DNAT --to 192.168.60.10:22
iptables        -A FORWARD     -s 10.9.0.2      -p tcp --dport 22   -j ACCEPT

# Allow 'admin' connection to 'jumpbox' TELNET
iptables -t nat -A POSTROUTING -s 192.168.60.10 -p tcp --sport 23 -j SNAT --to 10.9.0.254
iptables -t nat -A PREROUTING  -s 10.9.0.2      -p tcp --dport 23 -j DNAT --to 192.168.60.10
iptables        -A FORWARD     -s 10.9.0.2      -p tcp --dport 23 -j ACCEPT

Could someone please direct me to the solution?
Thanks in advance.

EDIT:

After several attempts I succeeded in my intent with these commands:

# Allow 'admin' connection to 'jumpbox' SSH (on 2222 port)
iptables -t nat -A PREROUTING  -s 10.9.0.2 -d 10.9.0.254    -p tcp --dport 2222 -j DNAT   --to 192.168.60.10:22
iptables        -A FORWARD     -s 10.9.0.2 -d 192.168.60.10 -p tcp --dport 22   -j ACCEPT
iptables -t nat -A POSTROUTING             -d 192.168.60.10 -p tcp --dport 22   -j SNAT   --to 192.168.60.254

# Allow 'admin' connection to 'jumpbox' TELNET
iptables -t nat -A PREROUTING  -s 10.9.0.2 -d 10.9.0.254    -p tcp --dport 23 -j DNAT   --to 192.168.60.10
iptables        -A FORWARD     -s 10.9.0.2 -d 192.168.60.10 -p tcp --dport 23 -j ACCEPT
iptables -t nat -A POSTROUTING             -d 192.168.60.10 -p tcp --dport 23 -j SNAT   --to 192.168.60.254

Now the problem becomes that if I try to connect using the internal IP:

$ telnet 192.168.60.10 23  # or
$ ssh -p2222 192.168.60.10

I am able to do this, but I have to block this behavior.

Giuseppe
  • 101
  • 2

1 Answers1

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I was able to achieve my goal with the following rules:

# ...

# Allow 'admin' connection to 'jumpbox' SSH (on 2222 port)
iptables -t nat -A PREROUTING  -s 10.9.0.2 -d 10.9.0.254                                -p tcp --dport 2222 -j DNAT   --to 192.168.60.10:22
iptables        -A FORWARD     -s 10.9.0.2 -d 192.168.60.10 -m conntrack --ctstate DNAT -p tcp --dport 22   -j ACCEPT
iptables -t nat -A POSTROUTING             -d 192.168.60.10                             -p tcp --dport 22   -j SNAT   --to 192.168.60.254

# Allow 'admin' connection to 'jumpbox' TELNET
iptables -t nat -A PREROUTING  -s 10.9.0.2 -d 10.9.0.254                                -p tcp --dport 23 -j DNAT   --to 192.168.60.10
iptables        -A FORWARD     -s 10.9.0.2 -d 192.168.60.10 -m conntrack --ctstate DNAT -p tcp --dport 23 -j ACCEPT
iptables -t nat -A POSTROUTING             -d 192.168.60.10                             -p tcp --dport 23 -j SNAT   --to 192.168.60.254
Giuseppe
  • 101
  • 2