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Full Discussion: iptables help with rules
Top Forums UNIX for Advanced & Expert Users iptables help with rules Post 302988724 by steadyonabix on Sunday 1st of January 2017 09:22:20 AM
Old 01-01-2017
iptables help with rules
Hi,

I've been struggling with this all morning and seem to have a blind spot on what the problem is. I'm trying to use iptables to block traffic on a little cluster of raspberry pi's but to allow ssh and ping traffic within it.

The cluster has a firewall server with a wifi card connecting to my home network and eth0 connection to a switch connecting the pi's within the cluster. All the other pi's just use the switch to talk to each on a network. They all use IP addresses in the range 10.10.1.2/5. The firewall pi uses 10.10.1.1 for eth0 and picks up a 192.168.1.122 address from my router on the wifi card.

I have this rule set that is currently preventing me from ssh'ing from the fwl to an internal pi on the cluster. I know that because if I clear the rules I can connect:

Code:
root@fwl:~# iptables -L -v
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
   70  5472 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:ssh ctstate NEW,RELATED,ESTABLISHED
    0     0 ACCEPT     all  --  lo     any     anywhere             anywhere
    0     0 ACCEPT     all  --  any    any     anywhere             anywhere             state RELATED,ESTABLISHED
    0     0 ACCEPT     icmp --  any    any     anywhere             anywhere             icmp echo-request
    0     0 ACCEPT     icmp --  any    any     anywhere             anywhere             icmp echo-reply
   59  8329 DROP       all  --  any    any     anywhere             anywhere

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
    0     0 DROP       all  --  any    any     anywhere             anywhere

Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination
   40  3304 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp spt:ssh ctstate NEW,RELATED,ESTABLISHED
    0     0 ACCEPT     all  --  any    lo      anywhere             anywhere
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:http state NEW
    0     0 ACCEPT     tcp  --  any    any     anywhere             anywhere             tcp dpt:domain state NEW
    0     0 ACCEPT     udp  --  any    any     anywhere             anywhere             udp dpt:domain state NEW
    0     0 ACCEPT     icmp --  any    any     anywhere             anywhere             icmp echo-reply
    0     0 ACCEPT     icmp --  any    any     anywhere             anywhere             icmp echo-request
   14  1032 DROP       all  --  any    any     anywhere             anywhere

Here is the script I use to create the rules:

Code:
root@fwl:~# cat fwl.cfg
#!/bin/sh

# Flushing all rules
iptables -F
iptables -X

# Setting default filter policy
iptables -P INPUT ACCEPT
iptables -P OUTPUT ACCEPT
iptables -P FORWARD ACCEPT

# Allow unlimited traffic on loopback
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# Allow ssh
iptables -I INPUT -p tcp  --dport 22 -m conntrack --ctstate NEW,RELATED,ESTABLISHED -j ACCEPT
iptables -I OUTPUT -p tcp --sport 22 -m conntrack --ctstate NEW,RELATED,ESTABLISHED -j ACCEPT

iptables -A OUTPUT -m state --state RELATED,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp --dport 80 -m state --state NEW -j ACCEPT
iptables -A OUTPUT -p tcp --dport 53 -m state --state NEW -j ACCEPT
iptables -A OUTPUT -p udp --dport 53 -m state --state NEW -j ACCEPT

iptables -A INPUT -m state --state RELATED,ESTABLISHED -j ACCEPT

# Allow ping
iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp --icmp-type echo-reply -j ACCEPT

# Setting default filter policy
iptables -A INPUT -j DROP
iptables -A OUTPUT -j DROP
iptables -A FORWARD -j DROP

I'm no expert on firewalls but I've been reading a lot this morning about setting up ssh in iptables and think the idea is to allow what you want and then append a drop of everything else after those rules.

Most of the pages I've looked at suggest doing this at the start of the rules:

Code:
iptables -A INPUT -j DROP
iptables -A OUTPUT -j DROP
iptables -A FORWARD -j DROP

and then relaxing the rules for ssh and ping afterwards, but I couldn't get that to work either.

Like I said though, I can connect if I flush the rules out.

Can anyone suggest where I'm going wrong?

Thanks

Steady
 

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