Shorewall Troubleshooting

Check the Errata

Check the Shorewall Errata to be sure that there isn't an update that you are missing for your version of the firewall.

Check the FAQs

Check the FAQs for solutions to common problems.

If the firewall fails to start

• shorewall debug start 2> /tmp/trace
• Look at the /tmp/trace file and see if that helps you determine what the problem is.
• If you still can't determine what's wrong then see the support page.

Your test environment

Many times when people have problems with Shorewall, the problem is actually an ill-conceived test setup. Here are several popular snafus:

• Port Forwarding where client and server are in the same subnet. See FAQ 2.
• Changing the IP address of a local system to be in the external subnet, thinking that Shorewall will suddenly believe that the system is in the 'net' zone.
• Multiple interfaces connected to the same HUB or Switch. Given the way that the Linux kernel respond to ARP "who-has" requests, this type of setup does NOT work the way that you expect it to.

If you are having connection problems:

If the appropriate policy for the connection that you are trying to make is ACCEPT, please DO NOT ADD ADDITIONAL ACCEPT RULES TRYING TO MAKE IT WORK. Such additional rules will NEVER make it work, they add clutter to your rule set and they represent a big security hole in the event that you forget to remove them later.

I also recommend against setting all of your policies to ACCEPT in an effort to make something work. That robs you of one of your best diagnostic tools - the "Shorewall" messages that Netfilter will generate when you try to connect in a way that isn't permitted by your rule set.

Check your log. If you don't see Shorewall messages, then your problem is probably NOT a Shorewall problem. If you DO see packet messages, it is an indication that you are missing one or more rules.

While you are troubleshooting, it is a good idea to clear two variables in /etc/shorewall/shorewall.conf:

LOGRATE=""
LOGBURST=""

This way, you will see all of the log messages being generated (be sure to restart shorewall after clearing these variables).

Example:

Let's look at the important parts of this message:

• all2all:REJECT - the packet was rejected under the "all"->"all" REJECT policy
• IN=eth2 - the packet entered the firewall via eth2
• OUT=eth1 - if accepted, the packet would be sent on eth1
• SRC=192.168.2.2 - the packet was sent by 192.168.2.2
• DST=192.168.1.3 - the packet is destined for 192.168.1.3
• PROTO=UDP - UDP Protocol
• DPT=53 - DNS

In this case, 192.168.2.2 was in the "dmz" zone and 192.168.1.3 is in the "loc" zone. I was missing the rule:

ACCEPT    dmz    loc    udp    53

Other Gotchas

• Seeing rejected/dropped packets logged out of the INPUT or FORWARD chains? This means that your zone definitions are screwed up and the host that is sending the packets isn't in any zone (using a /etc/shorewall/hosts file are you?).
• Remember that Shorewall doesn't automatically allow ICMP type 8 ("ping") requests to be sent between zones. If you want pings to be allowed between zones, you need a rule of the form:
  
      ACCEPT    <source zone>    <destination zone>    icmp    echo-request
  
  The ramifications of this can be subtle. For example, if you have the following in /etc/shorewall/nat:
  
      10.1.1.2    eth0    130.252.100.18
  
  and you ping 130.252.100.18, unless you have allowed icmp type 8 between the zone containing the system you are pinging from and the zone containing 10.1.1.2, the ping requests will be dropped. This is true even if you have NOT specified 'noping' for eth0 in /etc/shorewall/interfaces.
• If you specify "routefilter" for an interface, that interface must be up prior to starting the firewall.
• Is your routing correct? For example, internal systems usually need to be configured with their default gateway set to the IP address of their nearest firewall interface. One often overlooked aspect of routing is that in order for two hosts to communicate, the routing between them must be set up in both directions. So when setting up routing between A and B, be sure to verify that the route from B back to A is defined.
• Some versions of LRP (EigerStein2Beta for example) have a shell with broken variable expansion. You can get a corrected shell from the Shorewall Errata download site.
• Do you have your kernel properly configured? Click here to see my kernel configuration.
• Some features require the "ip" program. That program is generally included in the "iproute" package which should be included with your distribution (though many distributions don't install iproute by default). You may also download the latest source tarball from ftp://ftp.inr.ac.ru/ip-routing .
• If you have any entry for a zone in /etc/shorewall/hosts then the zone must be entirely defined in /etc/shorewall/hosts unless you have specified MERGE_HOSTS=Yes (Shorewall version 1.3.5 and later). For example, if a zone has two interfaces but only one interface has an entry in /etc/shorewall/hosts then hosts attached to the other interface will not be considered part of the zone.
• Problems with NAT? Be sure that you let Shorewall add all external addresses to be use with NAT unless you have set ADD_IP_ALIASES =No in /etc/shorewall/shorewall.conf.

Still Having Problems?

See the support page.

Last updated 8/29/2002 - Tom Eastep

Copyright © 2001, 2002 Thomas M. Eastep.