Tom Eastep 2004-04-19 2003-2004 Thomas M. Eastep Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover, and with no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License. Shorewall Traffic Accounting support was added in Shorewall release 1.4.7. Shorewall accounting rules are described in the file /etc/shorewall/accounting. By default, the accounting rules are placed in a chain called accounting and can thus be displayed using shorewall show accounting. All traffic passing into, out of or through the firewall traverses the accounting chain including traffic that will later be rejected by interface options such as tcpflags and maclist. If your kernel doesn't support the connection tracking match extension (Kernel 2.4.21) then some traffic rejected under norfc1918 will not traverse the accounting chain. The columns in the accounting file are as follows: ACTION - What to do when a match is found. Possible values are: COUNT- Simply count the match and continue trying to match the packet with the following accounting rules DONE- Count the match and don't attempt to match any following accounting rules. <chain> - The name of a chain to jump to. Shorewall will create the chain automatically. If the name of the chain is followed by :COUNT then a COUNT rule matching this rule will automatically be added to <chain>. Chain names must start with a letter, must be composed of letters and digits, and may contain underscores (_) and periods (.). Beginning with Shorewall version 1.4.8, chain names man also contain embedded dashes (-) and are not required to start with a letter. CHAIN - The name of the chain where the accounting rule is to be added. If empty or - then the accounting chain is assumed. SOURCE - Packet Source. The name of an interface, an address (host or net) or an interface name followed by : and a host or net address. DESTINATION - Packet Destination Format the same as the SOURCE column. PROTOCOL - A protocol name (from /etc/protocols) or a protocol number. DEST PORT - Destination Port number. Service name from /etc/services or port number. May only be specified if the protocol is TCP or UDP (6 or 17). SOURCE PORT- Source Port number. Service name from /etc/services or port number. May only be specified if the protocol is TCP or UDP (6 or 17). In all columns except ACTION and CHAIN, the values -,any and all are treated as wild-cards. The accounting rules are evaluated in the Netfilter filter table. This is the same environment where the rules file rules are evaluated and in this environment, DNAT has already occurred in inbound packets and SNAT has not yet occurred on outbound ones. Accounting rules are not stateful -- each rule only handles traffic in one direction. For example, if eth0 is your internet interface and you have a web server in your DMZ connected to eth1 then to count HTTP traffic in both directions requires two rules: #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE # PORT PORT DONE - eth0 eth1 tcp 80 DONE - eth1 eth0 tcp - 80 Associating a counter with a chain allows for nice reporting. For example: #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE # PORT PORT web:COUNT - eth0 eth1 tcp 80 web:COUNT - eth1 eth0 tcp - 80 web:COUNT - eth0 eth1 tcp 443 web:COUNT - eth1 eth0 tcp - 443 DONE web Now shorewall show web will give you a breakdown of your web traffic: [root@gateway shorewall]# shorewall show web Shorewall-1.4.6-20030821 Chain web at gateway.shorewall.net - Wed Aug 20 09:48:56 PDT 2003 Counters reset Wed Aug 20 09:48:00 PDT 2003 Chain web (4 references) pkts bytes target prot opt in out source destination 11 1335 tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 18 1962 tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:80 0 0 tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 0 0 tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:443 29 3297 RETURN all -- * * 0.0.0.0/0 0.0.0.0/0 [root@gateway shorewall]# Here is a slightly different example: #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE # PORT PORT web - eth0 eth1 tcp 80 web - eth1 eth0 tcp - 80 web - eth0 eth1 tcp 443 web - eth1 eth0 tcp - 443 COUNT web eth0 eth1 COUNT web eth1 eth0 Now shorewall show web simply gives you a breakdown by input and output: [root@gateway shorewall]# shorewall show accounting web Shorewall-1.4.6-20030821 Chains accounting web at gateway.shorewall.net - Wed Aug 20 10:27:21 PDT 2003 Counters reset Wed Aug 20 10:24:33 PDT 2003 Chain accounting (3 references) pkts bytes target prot opt in out source destination 8767 727K web tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 0 0 web tcp -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 11506 13M web tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:80 0 0 web tcp -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:443 Chain web (4 references) pkts bytes target prot opt in out source destination 8767 727K all -- eth0 eth1 0.0.0.0/0 0.0.0.0/0 11506 13M all -- eth1 eth0 0.0.0.0/0 0.0.0.0/0 [root@gateway shorewall]# Here's how the same example would be constructed on an HTTP server with only one interface (eth0). READ THE ABOVE CAREFULLY -- IT SAYS SERVER. If you want to account for web browsing, you have to reverse the rules below. #ACTION CHAIN SOURCE DESTINATION PROTOCOL DEST SOURCE # PORT PORT web - eth0 - tcp 80 web - - eth0 tcp - 80 web - eth0 - tcp 443 web - - eth0 tcp - 443 COUNT web eth0 COUNT web - eth0 Note that with only one interface, only the SOURCE (for input rules) or the DESTINATION (for output rules) is specified in each rule. Here's the output: [root@mail shorewall]# shorewall show accounting web Shorewall-1.4.7 Chains accounting web at mail.shorewall.net - Sun Oct 12 10:27:21 PDT 2003 Counters reset Sat Oct 11 08:12:57 PDT 2003 Chain accounting (3 references) pkts bytes target prot opt in out source destination 8767 727K web tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 11506 13M web tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:80 0 0 web tcp -- eth0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:443 0 0 web tcp -- * eth0 0.0.0.0/0 0.0.0.0/0 tcp spt:443 Chain web (4 references) pkts bytes target prot opt in out source destination 8767 727K all -- eth0 * 0.0.0.0/0 0.0.0.0/0 11506 13M all -- * eth0 0.0.0.0/0 0.0.0.0/0 [root@mail shorewall]# For an example of integrating Shorewall Accounting with MRTG, see http://www.nightbrawler.com/code/shorewall-stats/.