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blocking all internal traffic except incoming traffic from a specific ip on a single port

I’m trying to use IPtables to block all internal traffic with the exception of one server, here are my rules but when i telnet from another instance i can still connect….

-P INPUT ACCEPT
-P FORWARD ACCEPT
-P OUTPUT ACCEPT
-N DOCKER
-N DOCKER-ISOLATION-STAGE-1
-N DOCKER-ISOLATION-STAGE-2
-N DOCKER-USER
-A FORWARD -j DOCKER-USER
-A FORWARD -j DOCKER-ISOLATION-STAGE-1
-A FORWARD -o docker0 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o docker0 -j DOCKER
-A FORWARD -i docker0 ! -o docker0 -j ACCEPT
-A FORWARD -i docker0 -o docker0 -j ACCEPT
-A FORWARD -o br-383efc983cd2 -m conntrack --ctstate RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -o br-383efc983cd2 -j DOCKER
-A FORWARD -i br-383efc983cd2 ! -o br-383efc983cd2 -j ACCEPT
-A FORWARD -i br-383efc983cd2 -o br-383efc983cd2 -j ACCEPT
-A DOCKER -d 172.18.0.3/32 ! -i br-383efc983cd2 -o br-383efc983cd2 -p tcp -m tcp --dport 1080 -j ACCEPT
-A DOCKER-ISOLATION-STAGE-1 -i docker0 ! -o docker0 -j DOCKER-ISOLATION-STAGE-2
-A DOCKER-ISOLATION-STAGE-1 -i br-383efc983cd2 ! -o br-383efc983cd2 -j DOCKER-ISOLATION-STAGE-2
-A DOCKER-ISOLATION-STAGE-1 -j RETURN
-A DOCKER-ISOLATION-STAGE-2 -o docker0 -j DROP
-A DOCKER-ISOLATION-STAGE-2 -o br-383efc983cd2 -j DROP
-A DOCKER-ISOLATION-STAGE-2 -j RETURN
-A DOCKER-USER -s 10.0.1.253/32 -i eth1 -p tcp -m tcp --dport 22 -j ACCEPT
-A DOCKER-USER -m state --state ESTABLISHED -j ACCEPT
-A DOCKER-USER -i eth1 -j REJECT --reject-with icmp-port-unreachable
-A DOCKER-USER -j RETURN

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Answer

When debugging iptables I normally:

  • reset all the counter – ‘iptables -Z’
  • make the connection
  • then review the rule hits – ‘iptables -L -v -n |more’

This should give you some pointers as to which rule is passing the connection

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