[LARTC] offset mask usage in u32 filter

[LARTC] offset mask usage in u32 filter

[Walter Karshat]

iproute2 distribution in README.iproute2+tc includes
toward the end an example of usage of syntax 'offset
mask' as follows:

# Lookup hash table, if it is not fragmented frame
# Use protocol as hash key
$TC filter add dev eth1 parent 1:0 prio 5 handle ::1
u32 ht 800:: \
	match ip nofrag \
	offset mask 0x0F00 shift 6 \
	hashkey mask 0x00ff0000 at 8 \
	link 1:

Also, identical usage is shown in an example in Linux
- Advanced Networking Overview:
http://qos.ittc.ku.edu/howto/node48.html

I could find no explanation of this usage in LARTC,
and specifically, Section 12.4 on Hashing filters does
not use it.  Searches of the mailing list did not
yield an answer.  Review of tc code in f_u32.c showed
that in parse_offset() the arguments were assembled
into tc_u32_sel structure fields and passed into the
kernel.  However, I could not figure out what the
intent was in cls_u32.c for these fields.

I would much appreciate an explanation or pointers to
information.
  Walter

__________________________________
Do you Yahoo!?
Yahoo! SiteBuilder - Free, easy-to-use web site design software
http://sitebuilder.yahoo.com
_______________________________________________
LARTC mailing list / LARTC@mailman.ds9a.nl
http://mailman.ds9a.nl/mailman/listinfo/lartc HOWTO: http://lartc.org/