Traffic Shaping/Control

Shorewall has limited support for traffic shaping/control. In order to use traffic shaping under Shorewall, it is essential that you get a copy of the Linux Advanced Routing and Shaping HOWTO, version 0.3.0 or later. It is also necessary to be running Linux Kernel 2.4.18 or later.

Shorewall traffic shaping support consists of the following:

• A new TC_ENABLED parameter in /etc/shorewall.conf. Traffic Shaping also requires that you enable packet mangling.
• A new CLEAR_TC parameter in /etc/shorewall.conf (Added in Shorewall 1.3.13). When Traffic Shaping is enabled (TC_ENABLED=Yes), the setting of this variable determines whether Shorewall clears the traffic shaping configuration during Shorewall [re]start and Shorewall stop.
  
• /etc/shorewall/tcrules - A file where you can specify firewall marking of packets. The firewall mark value may be used to classify packets for traffic shaping/control.
  
• /etc/shorewall/tcstart - A user-supplied file that is sourced by Shorewall during "shorewall start" and which you can use to define your traffic shaping disciplines and classes. I have provided a sample that does table-driven CBQ shaping but if you read the traffic shaping sections of the HOWTO mentioned above, you can probably code your own faster than you can learn how to use my sample. I personally use HTB (see below). HTB support may eventually become an integral part of Shorewall since HTB is a lot simpler and better-documented than CBQ. As of 2.4.20, HTB is a standard part of the kernel but iproute2 must be patched in order to use it.
  
  In tcstart, when you want to run the 'tc' utility, use the run_tc function supplied by shorewall if you want tc errors to stop the firewall.
  
  You can generally use off-the-shelf traffic shaping scripts by simply copying them to /etc/shorewall/tcstart. I use The Wonder Shaper (HTB version) that way (i.e., I just copied wshaper.htb to /etc/shorewall/tcstart and modified it according to the Wonder Shaper README). WARNING: If you use use Masquerading or SNAT (i.e., you only have one external IP address) then listing internal hosts in the NOPRIOHOSTSRC variable in the wshaper[.htb] script won't work. Traffic shaping occurs after SNAT has already been applied so when traffic shaping happens, all outbound traffic will have as a source address the IP addresss of your firewall's external interface.
  
• /etc/shorewall/tcclear - A user-supplied file that is sourced by Shorewall when it is clearing traffic shaping. This file is normally not required as Shorewall's method of clearing qdisc and filter definitions is pretty general.

1. Set TC_ENABLED=Yes and CLEAR_TC=Yes
2. Supply an /etc/shorewall/tcstart script to configure your traffic shaping rules.
3. Optionally supply an /etc/shorewall/tcclear script to stop traffic shaping. That is usually unnecessary.
4. If your tcstart script uses the 'fwmark' classifier, you can mark packets using entries in /etc/shorewall/tcrules.

1. Set TC_ENABLED=Yes and CLEAR_TC=No
2. Do not supply /etc/shorewall/tcstart or /etc/shorewall/tcclear scripts.
4. If your tcstart script uses the 'fwmark' classifier, you can mark packets using entries in /etc/shorewall/tcrules.

Kernel Configuration

This screen shot show how I've configured QoS in my Kernel:

/etc/shorewall/tcrules

The fwmark classifier provides a convenient way to classify packets for traffic shaping. The /etc/shorewall/tcrules file provides a means for specifying these marks in a tabular fashion.

Normally, packet marking occurs in the PREROUTING chain before any address rewriting takes place. This makes it impossible to mark inbound packets based on their destination address when SNAT or Masquerading are being used. Beginning with Shorewall 1.3.12, you can cause packet marking to occur in the FORWARD chain by using the MARK_IN_FORWARD_CHAIN option in shorewall.conf.

Columns in the file are as follows:

• MARK - Specifies the mark value is to be assigned in case of a match. This is an integer in the range 1-255. Beginning with Shorewall version 1.3.14, this value may be optionally followed by ":" and either 'F' or 'P' to designate that the marking will occur in the FORWARD or PREROUTING chains respectively. If this additional specification is omitted, the chain used to mark packets will be determined by the setting of the MARK_IN_FORWARD_CHAIN option in shorewall.conf.
  
  Example - 5
  
• SOURCE - The source of the packet. If the packet originates on the firewall, place "fw" in this column. Otherwise, this is a comma-separated list of interface names, IP addresses, MAC addresses in Shorewall Format and/or Subnets.
  
  Examples
      eth0
      192.168.2.4,192.168.1.0/24
  
• DEST -- Destination of the packet. Comma-separated list of IP addresses and/or subnets.
  
• PROTO - Protocol - Must be the name of a protocol from /etc/protocol, a number or "all"
  
• PORT(S) - Destination Ports. A comma-separated list of Port names (from /etc/services), port numbers or port ranges (e.g., 21:22); if the protocol is "icmp", this column is interpreted as the destination icmp type(s).
  
• CLIENT PORT(S) - (Optional) Port(s) used by the client. If omitted, any source port is acceptable. Specified as a comma-separate list of port names, port numbers or port ranges.

Example 1 - All packets arriving on eth1 should be marked with 1. All packets arriving on eth2 and eth3 should be marked with 2. All packets originating on the firewall itself should be marked with 3.

Example 2 - All GRE (protocol 47) packets not originating on the firewall and destined for 155.186.235.151 should be marked with 12.

Example 3 - All SSH packets originating in 192.168.1.0/24 and destined for 155.186.235.151 should be marked with 22.

My Setup

While I am currently using the HTB version of The Wonder Shaper (I just copied wshaper.htb to /etc/shorewall/tcstart and modified it as shown in the Wondershaper README), I have also run with the following set of hand-crafted rules in my /etc/shorewall/tcstart file:

run_tc qdisc add dev eth0 root handle 1: htb default 30

run_tc class add dev eth0 parent 1: classid 1:1 htb rate 384kbit burst 15k

echo "   Added Top Level Class -- rate 384kbit"

run_tc class add dev eth0 parent 1:1 classid 1:10 htb rate 140kbit ceil 384kbit burst 15k prio 1
run_tc class add dev eth0 parent 1:1 classid 1:20 htb rate 224kbit ceil 384kbit burst 15k prio 0
run_tc class add dev eth0 parent 1:1 classid 1:30 htb rate 20kbit  ceil 384kbit burst 15k quantum 1500 prio 1

echo "   Added Second Level Classes -- rates 140kbit, 224kbit, 20kbit"

run_tc qdisc add dev eth0 parent 1:10 pfifo limit 5
run_tc qdisc add dev eth0 parent 1:20 pfifo limit 10
run_tc qdisc add dev eth0 parent 1:30 pfifo limit 5

echo "   Enabled PFIFO on Second Level Classes"

run_tc filter add dev eth0 protocol ip parent 1:0 prio 1 handle 1 fw classid 1:10
run_tc filter add dev eth0 protocol ip parent 1:0 prio 0 handle 2 fw classid 1:20
run_tc filter add dev eth0 protocol ip parent 1:0 prio 1 handle 3 fw classid 1:30

echo "   Defined fwmark filters"

My tcrules file that went with this tcstart file is shown in Example 1 above. You can look at my configuration to see why I wanted shaping of this type.

1. I wanted to allow up to 140kbits/second for traffic outbound from my DMZ (note that the ceiling is set to 384kbit so outbound DMZ traffic can use all available bandwidth if there is no traffic from the local systems or from my laptop or firewall).
2. My laptop and local systems could use up to 224kbits/second.
3. My firewall could use up to 20kbits/second.

Last Updated 3/19/2003 - Tom Eastep

Copyright © 2001, 2002, 2003 Thomas M. Eastep.