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[HOWTO] IPFW in-kernel nat port forwarding to jails

Jails with XigmaNAS
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Posts: 8
Joined: 23 Oct 2017 02:48
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[HOWTO] IPFW in-kernel nat port forwarding to jails


Post by grzs »

When I encountered many odd issues after flushing the ipfw rules and fiddling with new ones I tried to simply add redirect rules and it worked.

Basic concept:
I create a new NAT table for each jail to manage their redirects separately.
After this I had to tell the firewall when to use which NAT table.

I have a jail running a web server, what I want to reach at port 8088 instead of standard 80.
I create NAT table nr 11 for it.
I also want to insert the ipfw rules when I start the jail and delete them when I stop it (to avoid duplication with each restart), so I need two scripts for each jail. I can set them in TheBrig jail configuration form (in section 'Commands', made it visible by clicking to button 'More').
I give one as prestart (redirect_on.sh):

Code: Select all


# variables
nr=11 # NAT table nr, also ipfw rule nr, max 50 !!
pub_if=<outgoing interface>
jail_ip=<jail ip>

# initialize NAT table
ipfw add <$nr-1, e.g. 10> nat $nr ip from any to any <list of source ports, e.g. 8088> via $pub_if
ipfw add $nr nat $nr ip from $jail_ip <service port in jail, e.g. 80> to any via $pub_if

# port forwarding
# ipfw nat $nr config if $pub_if \
# redirect_port tcp <dest-ip-1>:<dest-port-1> <src-port-1>
# redirect_port udp <dest-ip-2>:<dest-port-2> <src-port-2>

ipfw nat $nr config if $pub_if \
	redirect_port tcp $jail_ip:80 8088 \

... and another one as afterstop (redirect_off.sh):

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# delete NAT rules
ipfw delete 10
ipfw delete 11

You can check your firewall and NAT state with these commands as root:

Code: Select all

ipfw show
ipfw nat show config

Posts: 1
Joined: 31 Mar 2020 04:52
Status: Offline

Re: [HOWTO] IPFW in-kernel nat port forwarding to jails


Post by mcfly »

I am interested to create something similar although I am confused as to what you write for your variables pub_if and jail_ip etc. I have setup a VNET as explained in your other how to and can ping from the jail to the host and from the host to the jail. I am thinking I need to forward all outgoing traffic from the jail to the host. in my case my LAN from my router is and the vlan is and the jail is I also read that the jail cannot change the packet routing so how can I get the outgoing traffic from the jail out to the WAN?

Would appreciate any help or guidance on this.


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