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+
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+
-
+
Shorewall FAQ
-
+
+
-
+
-
-
- |
+ |
+
+
-
+
Shorewall FAQs
- |
-
+
+
-
-
+
+
-
+
1. I want to forward UDP
- port 7777 to my my personal PC with IP address 192.168.1.5.
- I've looked everywhere and can't find how to do it.
+ port 7777 to my my personal PC with IP address 192.168.1.5.
+ I've looked everywhere and can't find how to do it.
-
+
1a. Ok -- I followed those instructions
- but it doesn't work.
-
+ but it doesn't work.
+
-
+
1b. I'm still having problems with
- port forwarding
-
+ port forwarding
+
2. I port forward www requests
- to www.mydomain.com (IP 130.151.100.69) to system 192.168.1.5
- in my local network. External clients can browse
+ to www.mydomain.com (IP 130.151.100.69) to system 192.168.1.5
+ in my local network. External clients can browse
http://www.mydomain.com but internal clients can't.
-
+
2a. I have a zone "Z" with an RFC1918
- subnet and I use static NAT to assign non-RFC1918
- addresses to hosts in Z. Hosts in Z cannot communicate
+ subnet and I use static NAT to assign non-RFC1918
+ addresses to hosts in Z. Hosts in Z cannot communicate
with each other using their external (non-RFC1918 addresses)
so they can't access each other using their DNS names.
-
+
3. I want to use Netmeeting
- or MSN Instant Messenger with Shorewall. What
-do I do?
+ or MSN Instant Messenger with Shorewall. What
+ do I do?
-
+
4. I just used an online port scanner
- to check my firewall and it shows some ports as 'closed'
- rather than 'blocked'. Why?
+ to check my firewall and it shows some ports as
+'closed' rather than 'blocked'. Why?
-
+
4a. I just ran an nmap UDP scan
- of my firewall and it showed 100s of ports as open!!!!
+ of my firewall and it showed 100s of ports as open!!!!
-
+
5. I've installed Shorewall and now
- I can't ping through the firewall
+ I can't ping through the firewall
-
+
6. Where are the log messages
- written and how do I change the destination?
+ written and how do I change the destination?
-
+
+
6a. Are there any log parsers
- that work with Shorewall?
-
+ that work with Shorewall?
+
6b. DROP messages on port 10619 are flooding the logs with their connect
- requests. Can i exclude these error messages for this port temporarily
- from logging in Shorewall?
-
-
+ requests. Can i exclude these error messages for this port temporarily
+ from logging in Shorewall?
+
+
6c. All day long I get a steady flow
- of these DROP messages from port 53 to some high numbered port.
- They get dropped, but what the heck are they?
-
-
+ of these DROP messages from port 53 to some high numbered port.
+ They get dropped, but what the heck are they?
+
+
6d. Why is the MAC address
- in Shorewall log messages so long? I thought MAC addresses were only
- 6 bytes in length.
-
-
+ in Shorewall log messages so long? I thought MAC addresses were only
+ 6 bytes in length.
+
+
7. When I stop Shorewall using
'shorewall stop', I can't connect to anything. Why doesn't that command
- work?
+ work?
-
+
8. When I try to start Shorewall
- on RedHat I get messages about insmod failing --
+ on RedHat I get messages about insmod failing --
what's wrong?
-
+
9. Why can't Shorewall detect
- my interfaces properly?
+ my interfaces properly?
-
+
10. What distributions does
- it work with?
+ it work with?
-
+
11. What features does it
support?
-
+
12. Is there a GUI?
-
+
13. Why do you call it "Shorewall"?
-
+
14. I'm connected via a cable modem
- and it has an internel web server that allows me to
+ and it has an internel web server that allows me to
configure/monitor it but as expected if I enable rfc1918
blocking for my eth0 interface, it also blocks the cable
modems web server.
-
+
14a. Even though it assigns public
- IP addresses, my ISP's DHCP server has an RFC 1918 address.
- If I enable RFC 1918 filtering on my external interface,
-my DHCP client cannot renew its lease.
+ IP addresses, my ISP's DHCP server has an RFC 1918
+address. If I enable RFC 1918 filtering on my external
+interface, my DHCP client cannot renew its lease.
-
+
15. My local systems can't see
- out to the net
+ out to the net
-
+
16. Shorewall is writing log messages
- all over my console making it unusable!
-
- 17. making it unusable!
+
+ 17. How do I find out why this traffic is getting
logged?
-
- 18. Is there any
-way to use aliased ip addresses with Shorewall, and
+
+ 18. Is there any
+ way to use aliased ip addresses with Shorewall, and
maintain separate rulesets for different IPs?
-
- 19. I have added entries
- to /etc/shorewall/tcrules but they don't seem to do
- anything. Why?
-
- 20. I have just set up
- a server. Do I have to change Shorewall to allow access to my
- server from the internet?
+
+ 19. I have added entries
+ to /etc/shorewall/tcrules but they don't seem to do
+ anything. Why?
+
+ 20. I have just set
+ up a server. Do I have to change Shorewall to allow access
+to my server from the internet?
+
+ 21. I see these strange
+ log entries occasionally; what are they?
+
+ 22. I have some iptables commands
+ that I want to run when Shorewall starts. Which file do
+ I put them in?
- 21. I see these strange
- log entries occasionally; what are they?
-
- 22. I have some iptables commands
- that I want to run when Shorewall starts. Which file do
-I put them in?
-
- 23. Why do you use such ugly fonts
- on your web site?
-
- 24. How can I allow conections
-to let's say the ssh port only from specific IP Addresses on the
-internet?
-
-
-
+ 23. Why do you use such ugly
+fonts on your web site?
+
+ 24. How can I allow conections
+ to let's say the ssh port only from specific IP Addresses on
+the internet?
+
+ 25. How to I tell which version of Shorewall
+I am running?
+
+
+
1. I want to forward UDP port 7777 to
- my my personal PC with IP address 192.168.1.5. I've looked
- everywhere and can't find how to do it.
+ my my personal PC with IP address 192.168.1.5. I've
+looked everywhere and can't find how to do it.
-
+
Answer: The first example in the rules file documentation shows how to
- do port forwarding under Shorewall. The format of a port-forwarding
- rule to a local system is as follows:
+ do port forwarding under Shorewall. The format of a
+port-forwarding rule to a local system is as follows:
-
+
-
+
-
-
- | ACTION |
- SOURCE |
- DESTINATION |
- PROTOCOL |
- PORT |
- SOURCE PORT |
- ORIG. DEST. |
-
-
- | DNAT |
- net |
- loc:<local IP address>[:<local
- port>] |
- <protocol> |
- <port #> |
-
- |
-
- |
-
+
+
+ | ACTION |
+ SOURCE |
+ DESTINATION |
+ PROTOCOL |
+ PORT |
+ SOURCE PORT |
+ ORIG. DEST. |
+
+
+ | DNAT |
+ net |
+ loc:<local IP
+address>[:<local port>] |
+ <protocol> |
+ <port #> |
+
+ |
+
+ |
+
-
+
-
+
-
+
-
+
So to forward UDP port 7777 to internal system 192.168.1.5,
- the rule is:
+ the rule is:
-
+
-
+
-
-
- | ACTION |
- SOURCE |
- DESTINATION |
- PROTOCOL |
- PORT |
- SOURCE PORT |
- ORIG. DEST. |
-
-
- | DNAT |
- net |
- loc:192.168.1.5 |
- udp |
- 7777 |
-
- |
-
- |
-
+
+
+ | ACTION |
+ SOURCE |
+ DESTINATION |
+ PROTOCOL |
+ PORT |
+ SOURCE PORT |
+ ORIG. DEST. |
+
+
+ | DNAT |
+ net |
+ loc:192.168.1.5 |
+ udp |
+ 7777 |
+
+ |
+
+ |
+
-
+
-
+
-
+
-
+
If
- you want to forward requests directed to a particular address ( <external
- IP> ) on your firewall to an internal system:
+ you want to forward requests directed to a particular address (
+<external IP> ) on your firewall to an internal system:
-
+
-
+
-
-
- | ACTION |
- SOURCE |
- DESTINATION |
- PROTOCOL |
- PORT |
- SOURCE PORT |
- ORIG. DEST. |
-
-
- | DNAT |
- net |
- loc:<local IP address>[:<local
- port>] |
- <protocol> |
- <port #> |
- - |
- <external IP> |
-
+
+
+ | ACTION |
+ SOURCE |
+ DESTINATION |
+ PROTOCOL |
+ PORT |
+ SOURCE PORT |
+ ORIG. DEST. |
+
+
+ | DNAT |
+ net |
+ loc:<local IP
+address>[:<local port>] |
+ <protocol> |
+ <port #> |
+ - |
+ <external IP> |
+
-
+
-
+
-
+
- Finally, if you need to forward a range of ports, in the PORT column
-specify the range as low-port:high-port.
-
+ Finally, if you need to forward a range of ports, in the PORT column
+ specify the range as low-port:high-port.
+
1a. Ok -- I followed those instructions
- but it doesn't work
+ but it doesn't work
-
+
Answer: That is usually the result of one of two things:
-
+
- - You are trying to test from
- inside your firewall (no, that won't work -- see You are trying to test from
+ inside your firewall (no, that won't work -- see FAQ #2).
- - You have a more basic problem
- with your local system such as an incorrect default gateway
- configured (it should be set to the IP address of your firewall's
- internal interface).
+ - You have a more basic problem
+ with your local system such as an incorrect default gateway
+ configured (it should be set to the IP address of your
+firewall's internal interface).
-
+
-
+
1b. I'm still having problems with port
- forwarding
- Answer: To further diagnose this problem:
-
+ forwarding
+ Answer: To further diagnose this
+problem:
+
- - As root, type "iptables -t nat -Z".
-This clears the NetFilter counters in the nat table.
- - Try to connect to the redirected port
- from an external host.
- - As root type "shorewall show nat"
- - Locate the appropriate DNAT rule. It
-will be in a chain called <source zone>_dnat ('net_dnat'
- in the above examples).
- - Is the packet count in the first column
- non-zero? If so, the connection request is reaching the firewall
- and is being redirected to the server. In this case, the problem
- is usually a missing or incorrect default gateway setting on
-the server (the server's default gateway should be the IP address
- of the firewall's interface to the server).
- - If the packet count is zero:
+ - As root, type "iptables -t nat -Z".
+ This clears the NetFilter counters in the nat table.
+ - Try to connect to the redirected port
+ from an external host.
+ - As root type "shorewall show nat"
+ - Locate the appropriate DNAT rule.
+It will be in a chain called <source zone>_dnat
+('net_dnat' in the above examples).
+ - Is the packet count in the first column
+ non-zero? If so, the connection request is reaching the firewall
+ and is being redirected to the server. In this case, the problem
+ is usually a missing or incorrect default gateway setting on
+ the server (the server's default gateway should be the IP address
+ of the firewall's interface to the server).
+ - If the packet count is zero:
-
+
- - the connection request is not reaching
- your server (possibly it is being blocked by your ISP); or
- - you are trying to connect to a secondary
- IP address on your firewall and your rule is only redirecting
- the primary IP address (You need to specify the secondary IP address
- in the "ORIG. DEST." column in your DNAT rule); or
- - your DNAT rule doesn't match the connection
- request in some other way. In that case, you may have to use
- a packet sniffer such as tcpdump or ethereal to further diagnose
- the problem.
-
+ - the connection request is not reaching
+ your server (possibly it is being blocked by your ISP); or
+ - you are trying to connect to a secondary
+ IP address on your firewall and your rule is only redirecting
+ the primary IP address (You need to specify the secondary IP address
+ in the "ORIG. DEST." column in your DNAT rule); or
+ - your DNAT rule doesn't match the
+connection request in some other way. In that case, you may
+have to use a packet sniffer such as tcpdump or ethereal to further
+diagnose the problem.
+
-
+
-
+
-
+
2. I port forward www requests to www.mydomain.com
- (IP 130.151.100.69) to system 192.168.1.5 in my local
-network. External clients can browse http://www.mydomain.com
-but internal clients can't.
+ (IP 130.151.100.69) to system 192.168.1.5 in my local
+ network. External clients can browse http://www.mydomain.com
+ but internal clients can't.
-
+
Answer: I have two objections to this setup.
-
+
-
+
If you insist on an IP solution to the accessibility problem
- rather than a DNS solution, then assuming that your
+ rather than a DNS solution, then assuming that your
external interface is eth0 and your internal interface
is eth1 and that eth1 has IP address 192.168.1.254 with subnet
192.168.1.0/24, in /etc/shorewall/rules, add:
-
+
-
-
+
+
-
+
-
-
- | ACTION |
- SOURCE |
- DESTINATION |
- PROTOCOL |
- PORT |
- SOURCE PORT |
- ORIG. DEST. |
-
-
- | DNAT |
- loc:192.168.1.0/24 |
- loc:192.168.1.5 |
- tcp |
- www |
- - |
- 130.151.100.69:192.168.1.254 |
-
+
+
+ | ACTION |
+ SOURCE |
+ DESTINATION |
+ PROTOCOL |
+ PORT |
+ SOURCE PORT |
+ ORIG. DEST. |
+
+
+ | DNAT |
+ loc:192.168.1.0/24 |
+ loc:192.168.1.5 |
+ tcp |
+ www |
+ - |
+ 130.151.100.69:192.168.1.254 |
+
-
+
-
+
-
-
+
+
+
+
That rule only works of course if you have a static external
- IP address. If you have a dynamic IP address and are
- running Shorewall 1.3.4 or later then include this in /etc/shorewall/params:
-
+ IP address. If you have a dynamic IP address and are
+ running Shorewall 1.3.4 or later then include this in
+/etc/shorewall/params:
+
+
+
ETH0_IP=`find_interface_address eth0`
-
+
+
+
and make your DNAT rule:
-
+
+
+
-
+
-
-
- | ACTION |
- SOURCE |
- DESTINATION |
- PROTOCOL |
- PORT |
- SOURCE PORT |
- ORIG. DEST. |
-
-
- | DNAT |
- loc:192.168.1.0/24 |
- loc:192.168.1.5 |
- tcp |
- www |
- - |
- $ETH0_IP:192.168.1.254 |
-
+
+
+ | ACTION |
+ SOURCE |
+ DESTINATION |
+ PROTOCOL |
+ PORT |
+ SOURCE PORT |
+ ORIG. DEST. |
+
+
+ | DNAT |
+ loc:192.168.1.0/24 |
+ loc:192.168.1.5 |
+ tcp |
+ www |
+ - |
+ $ETH0_IP:192.168.1.254 |
+
-
+
-
+
-
-
+
+
+
+
Using this technique, you will want to configure your DHCP/PPPoE
- client to automatically restart Shorewall each time
+ client to automatically restart Shorewall each time
that you get a new IP address.
-
+
2a. I have a zone "Z" with an RFC1918
- subnet and I use static NAT to assign non-RFC1918 addresses
- to hosts in Z. Hosts in Z cannot communicate with each other
- using their external (non-RFC1918 addresses) so they can't
- access each other using their DNS names.
+ subnet and I use static NAT to assign non-RFC1918 addresses
+ to hosts in Z. Hosts in Z cannot communicate with each other
+ using their external (non-RFC1918 addresses) so they can't
+ access each other using their DNS names.
-
+
Answer: This is another problem that is best solved
- using Bind Version 9 "views". It allows both external
-and internal clients to access a NATed host using the host's
- DNS name.
+ using Bind Version 9 "views". It allows both external
+ and internal clients to access a NATed host using the host's
+ DNS name.
-
+
Another good way to approach this problem is to switch from
- static NAT to Proxy ARP. That way, the hosts in Z have
- non-RFC1918 addresses and can be accessed externally and
-internally using the same address.
+ static NAT to Proxy ARP. That way, the hosts in Z have
+ non-RFC1918 addresses and can be accessed externally and
+ internally using the same address.
-
+
If you don't like those solutions and prefer routing all
Z->Z traffic through your firewall then:
-
+
a) Set the Z->Z policy to ACCEPT.
- b) Masquerade Z to itself.
-
- Example:
+ b) Masquerade Z to itself.
+
+ Example:
-
+
Zone: dmz
- Interface: eth2
- Subnet: 192.168.2.0/24
+ Interface: eth2
+ Subnet: 192.168.2.0/24
-
+
In /etc/shorewall/interfaces:
-
+
-
+
-
-
- | ZONE |
- INTERFACE |
- BROADCAST |
- OPTIONS |
-
-
- | dmz |
- eth2 |
- 192.168.2.255 |
-
- |
-
+
+
+ | ZONE |
+ INTERFACE |
+ BROADCAST |
+ OPTIONS |
+
+
+ | dmz |
+ eth2 |
+ 192.168.2.255 |
+
+ |
+
-
+
-
+
-
+
-
+
In /etc/shorewall/policy:
-
+
-
+
-
-
- | SOURCE |
- DESTINATION |
- POLICY |
- LIMIT:BURST |
-
-
- | dmz |
- dmz |
- ACCEPT |
-
- |
-
+
+
+ | SOURCE |
+ DESTINATION |
+ POLICY |
+ LIMIT:BURST |
+
+
+ | dmz |
+ dmz |
+ ACCEPT |
+
+ |
+
-
+
-
+
-
+
-
+
+
In /etc/shorewall/masq:
-
+
-
+
-
-
- | INTERFACE
- |
- SUBNET |
- ADDRESS |
-
-
- | eth2 |
- 192.168.2.0/24 |
-
- |
-
+
+
+ | INTERFACE
+ |
+ SUBNET |
+ ADDRESS |
+
+
+ | eth2 |
+ 192.168.2.0/24 |
+
+ |
+
-
+
-
+
-
+
-
+
3. I want to use Netmeeting or MSN Instant
- Messenger with Shorewall. What do I do?
+ Messenger with Shorewall. What do I do?
-
+
Answer: There is an H.323 connection
- tracking/NAT module that may help with Netmeeting.
- Look here for a solution
- for MSN IM but be aware that there are significant security risks involved
- with this solution. Also check the Netfilter mailing list
-archives at http://www.netfilter.org.
+ tracking/NAT module that may help with Netmeeting.
+ Look here for a solution
+ for MSN IM but be aware that there are significant security risks involved
+ with this solution. Also check the Netfilter mailing list
+ archives at http://www.netfilter.org.
-
+
4. I just used an online port scanner
- to check my firewall and it shows some ports as 'closed'
- rather than 'blocked'. Why?
+ to check my firewall and it shows some ports as 'closed'
+ rather than 'blocked'. Why?
-
+
Answer: The common.def included with version 1.3.x
- always rejects connection requests on TCP port 113
-rather than dropping them. This is necessary to prevent
-outgoing connection problems to services that use the 'Auth'
-mechanism for identifying requesting users. Shorewall also
-rejects TCP ports 135, 137 and 139 as well as UDP ports 137-139.
- These are ports that are used by Windows (Windows can
-be configured to use the DCE cell locator on port 135). Rejecting
+ always rejects connection requests on TCP port 113
+ rather than dropping them. This is necessary to prevent
+ outgoing connection problems to services that use the
+'Auth' mechanism for identifying requesting users. Shorewall
+ also rejects TCP ports 135, 137 and 139 as well as UDP ports
+ 137-139. These are ports that are used by Windows (Windows can
+ be configured to use the DCE cell locator on port 135). Rejecting
these connection requests rather than dropping them cuts down
slightly on the amount of Windows chatter on LAN segments connected
to the Firewall.
-
+
If you are seeing port 80 being 'closed', that's probably
- your ISP preventing you from running a web server
+ your ISP preventing you from running a web server
in violation of your Service Agreement.
-
+
4a. I just ran an nmap UDP scan of my
- firewall and it showed 100s of ports as open!!!!
+ firewall and it showed 100s of ports as open!!!!
-
+
Answer: Take a deep breath and read the nmap man page
- section about UDP scans. If nmap gets nothing
- back from your firewall then it reports the port as open.
- If you want to see which UDP ports are really open, temporarily
- change your net->all policy to REJECT, restart Shorewall
-and do the nmap UDP scan again.
+ section about UDP scans. If nmap gets nothing
+ back from your firewall then it reports the port as open.
+ If you want to see which UDP ports are really open, temporarily
+ change your net->all policy to REJECT, restart Shorewall
+ and do the nmap UDP scan again.
-
+
5. I've installed Shorewall and now I
- can't ping through the firewall
+ can't ping through the firewall
-
+
Answer: If you want your firewall to be totally open
- for "ping",
+ for "ping",
-
+
a) Create /etc/shorewall/common if it doesn't already exist.
-
- b) Be sure that the first command
-in the file is ". /etc/shorewall/common.def"
- c) Add the following to /etc/shorewall/common
-
+
+ b) Be sure that the first command
+ in the file is ". /etc/shorewall/common.def"
+ c) Add the following to /etc/shorewall/common
+
-
+
-
+
run_iptables -A icmpdef -p ICMP --icmp-type echo-request
- -j ACCEPT
-
-
- For a complete description of Shorewall 'ping' management,
- see this page.
-
+ -j ACCEPT
+
+
+ For a complete description of Shorewall 'ping' management,
+ see this page.
+
6. Where are the log messages written
- and how do I change the destination?
+ and how do I change the destination?
-
+
Answer: NetFilter uses the kernel's equivalent of
syslog (see "man syslog") to log messages. It always uses the LOG_KERN (kern)
facility (see "man openlog") and you get to choose the log level (again,
see "man syslog") in your policies
and rules. The destination for messaged
logged by syslog is controlled by /etc/syslog.conf (see "man syslog.conf").
- When you have changed /etc/syslog.conf, be sure to restart
- syslogd (on a RedHat system, "service syslog restart").
+ When you have changed /etc/syslog.conf, be sure to restart
+ syslogd (on a RedHat system, "service syslog restart").
-
+
By default, older versions of Shorewall ratelimited log messages
- through settings
-in /etc/shorewall/shorewall.conf -- If you want to log
+ through settings
+ in /etc/shorewall/shorewall.conf -- If you want to log
all messages, set:
-
-
-
+
6a. Are there any log parsers that work
- with Shorewall?
+ with Shorewall?
-
+
Answer: Here are several links that may be helpful:
-
+
-
+
-
+
http://www.shorewall.net/pub/shorewall/parsefw/
- http://www.fireparse.com
- http://cert.uni-stuttgart.de/projects/fwlogwatch
- http://www.logwatch.org
- http://gege.org/iptables
-
-
- I personnaly use Logwatch. It emails me a report each
- day from my various systems with each report summarizing the logged
- activity on the corresponding system.
-
+ http://www.logwatch.org
+ http://gege.org/iptables
+
+
+ I personnaly use Logwatch. It emails me a report
+each day from my various systems with each report summarizing the
+logged activity on the corresponding system.
+
6b. DROP messages on port 10619
- are flooding the logs with their connect requests. Can i exclude
- these error messages for this port temporarily from logging in Shorewall?
- Temporarily add the following rule:
-
- DROP net fw udp 10619
-
+ are flooding the logs with their connect requests. Can i exclude
+ these error messages for this port temporarily from logging in Shorewall?
+ Temporarily add the following rule:
+
+ DROP net fw udp 10619
+
6c. All day long I get a steady flow
- of these DROP messages from port 53 to some high numbered port. They
-get dropped, but what the heck are they?
-
-Jan 8 15:50:48 norcomix kernel: Shorewall:net2all:DROP:IN=eth0 OUT= MAC=00:40:c7:2e:09:c0:00:01:64:4a:70:00:08:00
SRC=208.138.130.16 DST=24.237.22.45 LEN=53 TOS=0x00 PREC=0x00
TTL=251 ID=8288 DF PROTO=UDP SPT=53 DPT=40275 LEN=33
- Answer: There are two possibilities:
-
+ of these DROP messages from port 53 to some high numbered port. They
+ get dropped, but what the heck are they?
+
+Jan 8 15:50:48 norcomix kernel: Shorewall:net2all:DROP:IN=eth0 OUT= MAC=00:40:c7:2e:09:c0:00:01:64:4a:70:00:08:00
SRC=208.138.130.16 DST=24.237.22.45 LEN=53 TOS=0x00 PREC=0x00
TTL=251 ID=8288 DF PROTO=UDP SPT=53 DPT=40275 LEN=33
+ Answer: There are two possibilities:
+
- - They are late-arriving replies to DNS queries.
- - They are corrupted reply packets.
-
+ - They are late-arriving replies to DNS queries.
+ - They are corrupted reply packets.
+
- You can distinguish the difference by setting the logunclean
- option (/etc/shorewall/interfaces)
- on your external interface (eth0 in the above example). If they get logged
- twice, they are corrupted. I solve this problem by using an /etc/shorewall/common
- file like this:
-
-
+ You can distinguish the difference by setting the logunclean
+ option (/etc/shorewall/interfaces)
+ on your external interface (eth0 in the above example). If they get logged
+ twice, they are corrupted. I solve this problem by using an /etc/shorewall/common
+ file like this:
+
+
#
# Include the standard common.def file
#
. /etc/shorewall/common.def
#
# The following rule is non-standard and compensates for tardy
# DNS replies
#
run_iptables -A common -p udp --sport 53 -mstate --state NEW -j DROP
-
- The above file is also include in all of my sample configurations
- available in the Quick Start
-Guides and in the common.def file in Shorewall 1.4.0 and later.
-
+
+ The above file is also include in all of my sample configurations
+ available in the Quick Start
+ Guides and in the common.def file in Shorewall 1.4.0 and later.
+
6d. Why is the MAC address in
- Shorewall log messages so long? I thought MAC addresses were only 6 bytes
- in length. What is labeled as the MAC address in a Shorewall log message
-is actually the Ethernet frame header. In contains:
-
-
+ Shorewall log messages so long? I thought MAC addresses were only 6 bytes
+ in length. What is labeled as the MAC address in a Shorewall log message
+ is actually the Ethernet frame header. In contains:
+
+
- - the destination MAC address (6 bytes)
- - the source MAC address (6 bytes)
- - the ethernet frame type (2 bytes)
-
+ - the destination MAC address (6 bytes)
+ - the source MAC address (6 bytes)
+ - the ethernet frame type (2 bytes)
+
- Example:
-
- MAC=00:04:4c:dc:e2:28:00:b0:8e:cf:3c:4c:08:00
-
+ Example:
+
+ MAC=00:04:4c:dc:e2:28:00:b0:8e:cf:3c:4c:08:00
+
- - Destination MAC address = 00:04:4c:dc:e2:28
- - Source MAC address = 00:b0:8e:cf:3c:4c
- - Ethernet Frame Type = 08:00 (IP Version 4)
-
+ - Destination MAC address = 00:04:4c:dc:e2:28
+ - Source MAC address = 00:b0:8e:cf:3c:4c
+ - Ethernet Frame Type = 08:00 (IP Version 4)
+
-
+
7. When I stop Shorewall using 'shorewall
- stop', I can't connect to anything. Why doesn't that command
- work?
+ stop', I can't connect to anything. Why doesn't that
+command work?
-
+
The 'stop' command is intended to place your firewall into
- a safe state whereby only those hosts listed in /etc/shorewall/routestopped'
- are activated. If you want to totally open up your firewall,
- you must use the 'shorewall clear' command.
+ a safe state whereby only those hosts listed in /etc/shorewall/routestopped'
+ are activated. If you want to totally open up your firewall,
+ you must use the 'shorewall clear' command.
-
+
8. When I try to start Shorewall on RedHat,
- I get messages about insmod failing -- what's wrong?
+ I get messages about insmod failing -- what's wrong?
-
+
Answer: The output you will see looks something like
- this:
+ this:
-
+
/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: init_module: Device or resource busy
Hint: insmod errors can be caused by incorrect module parameters, including invalid IO or IRQ parameters
/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: insmod
/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o failed
/lib/modules/2.4.17/kernel/net/ipv4/netfilter/ip_tables.o: insmod ip_tables failed
iptables v1.2.3: can't initialize iptables table `nat': iptables who? (do you need to insmod?)
Perhaps iptables or your kernel needs to be upgraded.
-
+
This is usually cured by the following sequence of commands:
-
+
-
-
+
+
service ipchains stop
chkconfig --delete ipchains
rmmod ipchains
-
+
+
+
Also, be sure to check the errata
- for problems concerning the version of iptables (v1.2.3)
- shipped with RH7.2.
-
+ for problems concerning the version of iptables (v1.2.3)
+ shipped with RH7.2.
+
-
+
9. Why can't Shorewall detect my interfaces
- properly?
+ properly?
-
+
I just installed Shorewall and when I issue the start command,
- I see the following:
+ I see the following:
-
-
+
+
Processing /etc/shorewall/shorewall.conf ...
Processing /etc/shorewall/params ...
Starting Shorewall...
Loading Modules...
Initializing...
Determining Zones...
Zones: net loc
Validating interfaces file...
Validating hosts file...
Determining Hosts in Zones...
Net Zone: eth0:0.0.0.0/0
Local Zone: eth1:0.0.0.0/0
Deleting user chains...
Creating input Chains...
...
-
+
+
+
Why can't Shorewall detect my interfaces properly?
-
+
+
+
Answer: The above output is perfectly normal. The
Net zone is defined as all hosts that are connected through eth0 and the
local zone is defined as all hosts connected through eth1
-
+
10. What Distributions does it work
with?
-
+
Shorewall works with any GNU/Linux distribution that includes
- the proper
-prerequisites.
+ the proper
+ prerequisites.
-
+
11. What Features does it have?
-
+
Answer: See the Shorewall
- Feature List.
+ Feature List.
-
+
12. Is there a GUI?
-
+
Answer: Yes. Shorewall support is included in Webmin
- 1.060 and later versions. See http://www.webmin.com
-
+ 1.060 and later versions. See http://www.webmin.com
+
-
+
13. Why do you call it "Shorewall"?
-
+
Answer: Shorewall is a concatenation of "Shoreline"
- (the city
- where I live) and "Firewall". The full name of
- the product is actually "Shoreline Firewall" but "Shorewall" is must
- more commonly used.
+ (the city
+ where I live) and "Firewall". The full name
+of the product is actually "Shoreline Firewall" but "Shorewall" is
+must more commonly used.
-
+
14. I'm connected via a cable modem
- and it has an internal web server that allows me to
+ and it has an internal web server that allows me to
configure/monitor it but as expected if I enable rfc1918
blocking for my eth0 interface (the internet one), it also
blocks the cable modems web server.
-
+
Is there any way it can add a rule before the rfc1918 blocking
- that will let all traffic to and from the 192.168.100.1
- address of the modem in/out but still block all other rfc1918
- addresses?
+ that will let all traffic to and from the 192.168.100.1
+ address of the modem in/out but still block all other rfc1918
+ addresses?
-
+
Answer: If you are running a version of Shorewall
earlier than 1.3.1, create /etc/shorewall/start and in it, place the
following:
-
-
+
+
run_iptables -I rfc1918 -s 192.168.100.1 -j ACCEPT
-
+
+
+
-
+
-
+
+
+ | SUBNET |
+ TARGET |
+
+
+ | 192.168.100.1 |
+ RETURN |
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Be sure that you add the entry ABOVE the entry for 192.168.0.0/16.
+
+
+
+
Note: If you add a second IP address to your external firewall
+ interface to correspond to the modem address, you must
+ also make an entry in /etc/shorewall/rfc1918 for that address.
+ For example, if you configure the address 192.168.100.2 on
+your firewall, then you would add two entries to /etc/shorewall/rfc1918:
+
+
+
+
+
+
+
+
- | SUBNET |
- TARGET |
-
-
- | 192.168.100.1 |
- RETURN |
-
+ SUBNET
+ |
+ TARGET
+ |
+
+
+ 192.168.100.1
+ |
+ RETURN
+ |
+
+
+ 192.168.100.2
+ |
+ RETURN
+ |
+
-
+
-
-
+
+
-
Be sure that you add the entry ABOVE the entry for 192.168.0.0/16.
-
-
-
-
Note: If you add a second IP address to your external firewall
- interface to correspond to the modem address, you must
-also make an entry in /etc/shorewall/rfc1918 for that address.
-For example, if you configure the address 192.168.100.2 on your
-firewall, then you would add two entries to /etc/shorewall/rfc1918:
-
-
-
-
-
-
-
-
-
- SUBNET
- |
- TARGET
- |
-
-
- 192.168.100.1
- |
- RETURN
- |
-
-
- 192.168.100.2
- |
- RETURN
- |
-
-
-
-
-
-
-
-
-
-
+
+
14a. Even though it assigns public
IP addresses, my ISP's DHCP server has an RFC 1918 address. If I enable
RFC 1918 filtering on my external interface, my DHCP client cannot renew
its lease.
-
+
+
+
The solution is the same as FAQ 14 above. Simply substitute
- the IP address of your ISPs DHCP server.
-
+ the IP address of your ISPs DHCP server.
+
15. My local systems can't see out to
- the net
+ the net
-
+
Answer: Every time I read "systems can't see out to
- the net", I wonder where the poster bought computers
-with eyes and what those computers will "see" when things
-are working properly. That aside, the most common causes of
-this problem are:
+ the net", I wonder where the poster bought computers
+ with eyes and what those computers will "see" when things
+ are working properly. That aside, the most common causes
+of this problem are:
-
+
- -
+
-
-
+
The default gateway on each local system isn't set to
- the IP address of the local firewall interface.
-
- -
+ the IP address of the local firewall interface.
+
+ -
-
+
The entry for the local network in the /etc/shorewall/masq
- file is wrong or missing.
-
- -
+ file is wrong or missing.
+
+ -
-
+
The DNS settings on the local systems are wrong or the
- user is running a DNS server on the firewall and hasn't
- enabled UDP and TCP port 53 from the firewall to the
-internet.
-
+ user is running a DNS server on the firewall and
+hasn't enabled UDP and TCP port 53 from the firewall
+to the internet.
+
-
+
-
+
16. Shorewall is writing log messages
- all over my console making it unusable!
+ all over my console making it unusable!
-
+
Answer: "man dmesg" -- add a suitable 'dmesg' command
- to your startup scripts or place it in /etc/shorewall/start.
- Under RedHat, the max log level that is sent to the
+ to your startup scripts or place it in /etc/shorewall/start.
+ Under RedHat, the max log level that is sent to the
console is specified in /etc/sysconfig/init in the LOGLEVEL
variable.
-
-
+
+
+
17. How do I find out why this traffic is getting
- logged?
- Answer: Logging occurs out of
-a number of chains (as indicated in the log message) in Shorewall:
-
+ logged?
+ Answer: Logging occurs out of
+ a number of chains (as indicated in the log message) in
+Shorewall:
+
+
- - man1918 - The destination
- address is listed in /etc/shorewall/rfc1918 with a logdrop
- target -- see /etc/shorewall/rfc1918.
- - rfc1918 - The source address
- is listed in /etc/shorewall/rfc1918 with a logdrop target
- -- see /etc/shorewall/rfc1918.
- - all2<zone>, <zone>2all
- or all2all - You have aman1918 - The destination
+ address is listed in /etc/shorewall/rfc1918 with a logdrop
+ target -- see /etc/shorewall/rfc1918.
+ - rfc1918 - The source address
+ is listed in /etc/shorewall/rfc1918 with a logdrop target
+ -- see /etc/shorewall/rfc1918.
+ - all2<zone>, <zone>2all
+ or all2all - You have a policy that specifies a log level
- and this packet is being logged under that policy. If you intend
- to ACCEPT this traffic then you need a rule to that effect.
-
- - <zone1>2<zone2>
- - Either you have a
+
+ - <zone1>2<zone2>
+ - Either you have a
policy for <zone1> to <zone2>
that specifies a log level and this packet is being logged
under that policy or this packet matches a rule that includes a log level.
- - <interface>_mac - The packet
- is being logged under the maclist <interface>_mac - The packet
+ is being logged under the maclist interface option.
-
- - logpkt - The packet is being
- logged under the logunclean
+
- logpkt - The packet is
+being logged under the logunclean interface option.
- - badpkt - The packet is being
- logged under the dropunclean badpkt - The packet is
+being logged under the dropunclean interface option as specified
in the LOGUNCLEAN setting in /etc/shorewall/shorewall.conf.
- - blacklst - The packet is
-being logged because the source IP is blacklisted in the /etc/shorewall/blacklist file.
- - newnotsyn - The packet is
- being logged because it is a TCP packet that is not part
-of any current connection yet it is not a syn packet. Options
-affecting the logging of such packets include NEWNOTSYN
- and LOGNEWNOTSYN in blacklst - The packet
+is being logged because the source IP is blacklisted in
+the /etc/shorewall/blacklist
+ file.
+ - newnotsyn - The packet
+is being logged because it is a TCP packet that is not part
+ of any current connection yet it is not a syn packet. Options
+ affecting the logging of such packets include NEWNOTSYN
+ and LOGNEWNOTSYN in /etc/shorewall/shorewall.conf.
- - INPUT or FORWARD -
-The packet has a source IP address that isn't in any of your
-defined zones ("shorewall check" and look at the printed zone
-definitions) or the chain is FORWARD and the destination IP isn't
-in any of your defined zones.
- - logflags - The packet is being logged
- because it failed the checks implemented by the tcpflags interface option.
-
-
+ - INPUT or FORWARD
+- The packet has a source IP address that isn't in any of
+your defined zones ("shorewall check" and look at the printed
+zone definitions) or the chain is FORWARD and the destination IP
+ isn't in any of your defined zones.
+ - logflags - The packet is being logged
+ because it failed the checks implemented by the tcpflags
+ interface option.
+
+
+
-
+
18. Is there any way to use aliased ip addresses
- with Shorewall, and maintain separate rulesets for different
- IPs?
- Answer: Yes. You simply use the IP
-address in your rules (or if you use NAT, use the local IP address
-in your rules). Note: The ":n" notation (e.g., eth0:0)
-is deprecated and will disappear eventually. Neither iproute
- (ip and tc) nor iptables supports that notation so neither does
- Shorewall.
-
- Example 1:
-
- /etc/shorewall/rules
-
+ with Shorewall, and maintain separate rulesets for different
+ IPs?
+ Answer: Yes. You simply use the
+IP address in your rules (or if you use NAT, use the local
+IP address in your rules). Note: The ":n" notation (e.g.,
+eth0:0) is deprecated and will disappear eventually. Neither
+iproute (ip and tc) nor iptables supports that notation so neither
+ does Shorewall.
+
+ Example 1:
+
+ /etc/shorewall/rules
+
# Accept AUTH but only on address 192.0.2.125
ACCEPT net fw:192.0.2.125 tcp auth
- Example
- 2 (NAT):
-
- /etc/shorewall/nat
-
+ Example
+ 2 (NAT):
+
+ /etc/shorewall/nat
+
192.0.2.126 eth0 10.1.1.126
- /etc/shorewall/rules
-
+ /etc/shorewall/rules
+
# Accept HTTP on 192.0.2.126 (a.k.a. 10.1.1.126)
ACCEPT net loc:10.1.1.126 tcp www
- Example 3 (DNAT):
-
+ Example 3 (DNAT):
+
# Forward SMTP on external address 192.0.2.127 to local system 10.1.1.127
DNAT net loc:10.1.1.127 tcp smtp - 192.0.2.127
-
+
19. I have added entries to /etc/shorewall/tcrules
- but they don't seem to do anything. Why?
- You probably haven't set TC_ENABLED=Yes in /etc/shorewall/shorewall.conf
- so the contents of the tcrules file are simply being ignored.
-
+ but they don't seem to do anything. Why?
+ You probably haven't set TC_ENABLED=Yes in
+/etc/shorewall/shorewall.conf so the contents of the tcrules
+file are simply being ignored.
+
20. I have just set up a server. Do I have
- to change Shorewall to allow access to my server from the internet?
-
- Yes. Consult the
+
+ Yes. Consult the QuickStart guide that you
used during your initial setup for information about how to set up
rules for your server.
-
+
21. I see these strange log entries occasionally;
- what are they?
-
-
+ what are they?
+
+
-
+
Nov 25 18:58:52 linux kernel: Shorewall:net2all:DROP:IN=eth1 OUT= MAC=00:60:1d:f0:a6:f9:00:60:1d:f6:35:50:08:00
SRC=206.124.146.179 DST=192.0.2.3 LEN=56 TOS=0x00 PREC=0x00 TTL=110 ID=18558 PROTO=ICMP TYPE=3 CODE=3
[SRC=192.0.2.3 DST=172.16.1.10 LEN=128 TOS=0x00 PREC=0x00 TTL=47 ID=0 DF PROTO=UDP SPT=53 DPT=2857 LEN=108 ]
-
- 192.0.2.3 is external on my firewall... 172.16.0.0/24
- is my internal LAN
-
- Answer: While most people associate the Internet
- Control Message Protocol (ICMP) with 'ping', ICMP is a key piece
- of the internet. ICMP is used to report problems back to the sender
- of a packet; this is what is happening here. Unfortunately, where
-NAT is involved (including SNAT, DNAT and Masquerade), there are
-a lot of broken implementations. That is what you are seeing with these
-messages.
-
- Here is my interpretation of what is happening --
-to confirm this analysis, one would have to have packet sniffers
-placed a both ends of the connection.
-
- Host 172.16.1.10 behind NAT gateway 206.124.146.179
- sent a UDP DNS query to 192.0.2.3 and your DNS server tried to
-send a response (the response information is in the brackets -- note
-source port 53 which marks this as a DNS reply). When the response was
-returned to to 206.124.146.179, it rewrote the destination IP TO 172.16.1.10
+
+ 192.0.2.3 is external on my firewall... 172.16.0.0/24
+ is my internal LAN
+
+ Answer: While most people associate the
+Internet Control Message Protocol (ICMP) with 'ping', ICMP is
+a key piece of the internet. ICMP is used to report problems back
+to the sender of a packet; this is what is happening here. Unfortunately,
+where NAT is involved (including SNAT, DNAT and Masquerade), there
+are a lot of broken implementations. That is what you are seeing with
+ these messages.
+
+ Here is my interpretation of what is happening
+-- to confirm this analysis, one would have to have packet sniffers
+ placed a both ends of the connection.
+
+ Host 172.16.1.10 behind NAT gateway 206.124.146.179
+ sent a UDP DNS query to 192.0.2.3 and your DNS server tried to
+ send a response (the response information is in the brackets -- note
+ source port 53 which marks this as a DNS reply). When the response was
+ returned to to 206.124.146.179, it rewrote the destination IP TO 172.16.1.10
and forwarded the packet to 172.16.1.10 who no longer had a connection
on UDP port 2857. This causes a port unreachable (type 3, code 3)
to be generated back to 192.0.2.3. As this packet is sent back through
@@ -1236,49 +1251,57 @@ all2all chain. I have also seen cases where the source IP in the ICMP
itself isn't set back to the external IP of the remote NAT gateway; that
causes your firewall to log and drop the packet out of the rfc1918 chain
because the source IP is reserved by RFC 1918.
-
+
22. I have some iptables commands that
- I want to run when Shorewall starts. Which file do I put them
- in?
- You can place these commands in one of the run when Shorewall starts. Which file do I put them
+ in?
+ You can place these commands in one of the Shorewall Extension Scripts. Be
sure that you look at the contents of the chain(s) that you will be modifying
- with your commands to be sure that the commands will do what they
-are intended. Many iptables commands published in HOWTOs and other instructional
- material use the -A command which adds the rules to the end of the
-chain. Most chains that Shorewall constructs end with an unconditional
-DROP, ACCEPT or REJECT rule and any rules that you add after that will
-be ignored. Check "man iptables" and look at the -I (--insert) command.
-
+ with your commands to be sure that the commands will do what they
+ are intended. Many iptables commands published in HOWTOs and other
+instructional material use the -A command which adds the rules to the
+end of the chain. Most chains that Shorewall constructs end with an
+unconditional DROP, ACCEPT or REJECT rule and any rules that you add
+after that will be ignored. Check "man iptables" and look at the -I (--insert)
+command.
+
23. Why do you use such ugly fonts on your
- web site?
- The Shorewall web site is almost font neutral (it doesn't
-explicitly specify fonts except on a few pages) so the fonts you see
-are largely the default fonts configured in your browser. If you don't
-like them then reconfigure your browser.
-
+ web site?
+ The Shorewall web site is almost font neutral (it doesn't
+ explicitly specify fonts except on a few pages) so the fonts you see
+ are largely the default fonts configured in your browser. If you don't
+ like them then reconfigure your browser.
+
24. How can I allow conections to let's say
- the ssh port only from specific IP Addresses on the internet?
- In the SOURCE column of the rule, follow "net" by a colon and
-a list of the host/subnet addresses as a comma-separated list.
-
- net:<ip1>,<ip2>,...
- Example:
-
+ the ssh port only from specific IP Addresses on the internet?
+ In the SOURCE column of the rule, follow "net" by a colon and
+ a list of the host/subnet addresses as a comma-separated list.
+
+ net:<ip1>,<ip2>,...
+ Example:
+
ACCEPT net:192.0.2.16/28,192.0.2.44 fw tcp 22
-
-
-
+
- Last updated 2/18/2003 - Tom Eastep
-
+
+25. How to I tell which version of Shorewall
+I am running?
+
+ At the shell prompt, type:
+
+ /sbin/shorewall version
+
+ Last updated 2/22/2003 - Tom Eastep
+
Copyright ©
2001, 2002, 2003 Thomas M. Eastep.
-
+
+
+
-
+