The new version of the ZPH patch is based on the same idea - modify some information about the packets that belong to a SQUID HIT response. The older version simply used to put these packets in a predefined (at squid compilation time) class. It really works fine, but it is not possible to separate the SQUID cache engine from the QoS policing machine. It also does not allow you to re-classify those HIT packets in any way.
In order to overcome those limitations I had to mark the HIT packets in a proper
way. There are generally two options here: 1. Use some sort of netfilter voodoo
(no offence here, really) to set the inner 32-bit mark field associated with
every packet traversing the kernel; 2. Use the TOS field available in the IP
In case 1 - you have the same problem - no easy way to separate the SQUID engine from the QoS - these marks are internal to linux kernel and are not transmitted with the packets. In case 2 - the TOS field seems a better choice, but you normally can't set it to just anything you want (not absolutely true). Furthermore - TOS value is not garanteed to be preserved when packet is travelling through the network. Many devices may alter this field.
I choosed a third way: add an option to the IP header of HIT packets. IP options are part of the standart IP protocol implementation, and when reviewing the RFC791, I came accross a very convinient one. The option that my patch uses is called Stream Identifier (directly from RFC791, page 21):
I have no idea what SATNET is, after all the date of the RFC is September, 1981, but I do know this is a valid option. It will be copied on fragmentation (I tested it myself, using Cisco and linux routers). It will survive an arbitrary number of hops, without being disturbed - even NAT won't spoil it !
|10001000|00000100| Stream ID |
This option provides a way for the 16-bit SATNET stream
identifier to be carried through networks that do not support
the stream concept.
Must be copied on fragmentation.
$TC filter add dev $LANDEV parent 1:0 protocol ip prio 1 u32 \
match ip protocol 0x6 0xff \
match u32 0x8804ABCD 0xffffffff at 20 \
That's all folks !
You simply put every HIT packet in your fast class (1:60 in this example). This class should have a very low rate (1 kbit is a good number), but its ceil should be the maximum possible bandwidth of the interface.
Do not forget to put your own filters before/after this one !
tar -zxvf squid-2.5.STABLEX.tar.gz3. Change to SQUID's source directory and apply the patch (this assumes you have downloaded the latest patch one directory above SQUID's source):
or, for the bzip2 archive:
tar -jxvf squid-2.5.STABLEX.tar.bz2
cd squid-2.5.STABLEX4. Follow SQUID's INSTALL guide to configure, compile and install the engine.
patch -p1 < ../squid-2.5.STABLEX-option-marking-zph.diff
tc -s class show dev eth1where you substitute eth1 with your internal (where the clients are connected) device name.