Need help understanding tc filter

[nathan11]

Hello
In my lost time I turn to linux in particular TC filter and at the moment I can't understand something about tc filter.
I give you an example:
tc filter add dev eth0 parent 1:0 protocol ip prio 1 u32 match ip sport 25500 0xffff flowid 1:1
What does 0xffff mean in this rule and I also know there is 0xfc00 ,0xff but can't find on the net;
Thank you and sorry for my english

[lleachii]

@nathan11

What does 0xffff mean in this rule and I also know there is 0xfc00 ,0xff but can't find on the net;

It is the match range (or mask, noted in bits) of the value you're editing in decimal value.

For example, Internet Protocol specifies there's 65,535 TCP and UDP ports, respectively.

65535 == 0xffff

@nathan11

25500 0xffff

This means: "match port 25500" (i.e. a single port).

A mathematical example provided here (see the section entitled "dst-port"): https://infocenter.nokia.com/public/770562R1A/topic/com.sar.system/html/security-commands.html?cp=9_2_10_1_0_2#i1635807

@nathan11

but can't find on the net

Refrences:

• https://tldp.org/HOWTO/Adv-Routing-HOWTO/lartc.qdisc.filters.html
• https://tldp.org/HOWTO/Linux+IPv6-HOWTO/ch21s02.html

@nathan11

0xfc00 ,

0xfc00 == 64512

(1023 less than 65536)

Would mean "match port x thru x +1023".

Lastly:

0xff == 255

[nathan11]

thank you very much for all these explanations

[nathan11]

One last question if I create a qdisc I have to assign it to all the interfaces in my case eth0, eth1, br0

[lleachii]

• Can you explain how this is related to your OpenWrt device?
• Model of device?
• OpenWrt version?

Perhaps we can better assist if we know what you wish to setup.

[nathan11]

I am on an x86 version 22.03.3 I would like to set up a qdisc prio for my local network by classifying some port in priority.
I've done it before but I just want to refine