[LARTC] Re: LARTC Digest, Vol 31, Issue 25

[Vadtec <vadtec@vadtec.net>]

>
> Message: 6 Date: Tue, 18 Sep 2007 10:44:42 +0200 From: Michal Soltys 
> <nozo@ziu.info> Subject: Re: [LARTC] I'm having an issue with u32 
> masking To: lartc@mailman.ds9a.nl Message-ID: 
> <46EF8FFA.6070707@ziu.info> Content-Type: text/plain; 
> charset=ISO-8859-1; format=flowed Vadtec wrote:
>> > Is this how tc is supposed to work? Does it only match on the value it 
>> > is given based on whether or not the mask matches? IE: u16 0x1a00 0x1a0f 
>> > at 22 (dest port 6656 ONLY), u16 0x1a0b 0x1a0f at 22 (dest port 6667 ONLY)
>> > 
>> > If so, how can you match a range of ports (in my example, or a range of 
>> > anything for that matter) in tc?
>> > 
>>     
>
> Try:
>
> match u16 0x1a00 0xfff0
>
> Mask is first applied to the value in the packet, then it's tested 
> against your (0x1a00) value
Can you please explain this further?

You are saying that its ORed with the value? Or is it ANDed? Or maybe 
XORed? What operation are they applying to the value? Working from what 
I have done with other bit masking operations, I am assuming that the 
mask is ANDed with the value in the packet. Then I would assume you OR 
the check with the resulting value. But I am not sure.

I would expect the mask to be applied to the value. It doesn't make 
sense to apply it to the check, because then you would simply match the 
highest possible value of the check+mask.


Vadtec
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