[iproute2] tc pedit modify ethhdr ?

[Xiaofei Wu]

Hi all,

I want to modify a packet's h_dest and h_source in structethhdr { } .

in tc / m_pedit.c
------

36 explain(void)
37 {
38 fprintf(stderr, "Usage: ... pedit munge <MUNGE>\n");
39 fprintf(stderr,
40 "Where: MUNGE := <RAW>|<LAYERED>\n"
41 "\t<RAW>:= <OFFSETC>[ATC]<CMD>\n "
42 "\t\tOFFSETC:= offset <offval> <u8|u16|u32>\n "
43 "\t\tATC:= at <atval> offmask <maskval> shift <shiftval>\n "
44 "\t\tNOTE: offval is byte offset, must be multiple of 4\n "
45 "\t\tNOTE: maskval is a 32 bit hex number\n "
46 "\t\tNOTE: shiftval is a is a shift value\n "
47 "\t\tCMD:= clear | invert | set <setval>| retain\n "
48 "\t<LAYERED>:= ip <ipdata> | ip6 <ip6data> \n "
49 " \t\t| udp <udpdata> | tcp <tcpdata> | icmp <icmpdata> \n"
50 "For Example usage look at the examples directory\n");
51
52 }
------

OFFSETC:= offset <offval> <u8|u16|u32>
NOTE: offval is byte offset, must be multiple of 4

but the size of ethhdr is 14 bytes, 14 is not multiple of 4 .
How to use 'tc ... pedit ...' modify a packet's h_dest and h_source
of ethhdr ?
Use ' ... pedit munge offset -14 u16 set 0x0090 munge offset -12 u32 set 0x9600030a ... ' or
use ' ... pedit munge offset -16 u32 ... munge offset -12 ... ' ?

--
Wu

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[jamal]

On Wed, 2010-03-24 at 05:31 -0700, Xiaofei Wu wrote:

> but the size of ethhdr is 14 bytes, 14 is not multiple of 4 .
> How to use 'tc ... pedit ...' modify a packet's h_dest and h_source
> of ethhdr ?
> Use ' ... pedit munge offset -14 u16 set 0x0090 munge offset -12 u32 set 0x9600030a ... ' or
> use ' ... pedit munge offset -16 u32 ... munge offset -12 ... ' ?
>

0 is at ip header.
dst MAC starts at -14
src MAC at -8
ethertype at -2

Example:
tc filter add dev eth0 parent ffff: protocol ip prio 10 u32 \
match ip src 192.168.1.10/32 flowid 1:2 \
action pedit munge offset -14 u16 set 0x0000 \
munge offset -12 u32 set 0x00010100 \
munge offset -8 u32 set 0x0aaf0100 \
munge offset -4 u32 set 0x0008ec06 pipe \
action mirred egress redirect dev eth1

cheers,
jamal

[Xiaofei Wu]

I made a test like your example.
The terminal prints:
parse_cmd argc 20 set offset -14 length 2
pack_key16: Final val 90000000 mask 0000ffff
parse_cmd done argc 18 munge offset -16 length 2

what's the meaning of the above 3 lines; It modify the value of -16,-15,-14,-13 , or just modify -14,-13 ?
If it modified -16,-15 , would it cause any problems?

Thanks.

--
Wu

[jamal]

I put some effort in responding to you. Please put some
effort in testing it.

cheers,
jamal

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