Re: Marking packets by mac addr using tc filter u32 match?

Linux Advanced Routing and Traffic Control

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Hi,
Forgive me if I point out the obvious. Remember that ARP isn't an IP protocol it's a peer protocol to IP. In the tc filters shown below the protocol is IP and the negative offset works on a IP packet but I suspect that an ARP packet isn't accessible with this technique. If I ubstitute IP for ARP in the filter statement it isn't accepted.

Regards Mike D.

Kristiadi Himawan wrote:


it's should be 0x0806 0xffff ?
or you have the example how to catch that kind of traffic

gypsy wrote:

Kristiadi Himawan wrote:
It's also match to this kind of traffic ?

17:16:53.740978 arp who-has 192.43.165.29 tell 192.43.165.30
17:16:53.752482 arp reply 192.43.165.29 is-at 00:04:c1:b5:bd:f1
17:16:53.812889 arp who-has 192.43.162.194 tell 192.43.162.193
17:16:53.812922 arp reply 192.43.162.194 is-at 00:08:c7:c9:a3:17


No.  The 'match u16 0x0800 0xffff' says to ignore ARP.

Lee Sanders wrote:

You haven't done a search on past posts...

the u32 can be used to match any bit in the ip header. Before the ip header, there is a frame header. In that frame header you can find the src and dst mac address. You can trick the u32 filter in using the frame header if you
use negative offsets.

Decimal Offset  Description
-14:    DST MAC, 6 bytes
-8:     SRC MAC, 6 bytes
-2:     Eth PROTO, 2 bytes, eg. ETH_P_IP
0:      Protocol header (IP Header)

Where PPPP is the Eth Proto Code (from linux/include/linux/if_ether.h):
ETH_P_IP= IP = match u16 0x0800
Where your MAC = M0M1M2M3M4M5

Egress (match Dst MAC):
... match u16 0xPPPP 0xFFFF at -2 match u32 0xM2M3M4M5 0xFFFFFFFF at -12 match
u16 0xM0M1 0xFFFF at -14

Ingress (match Src MAC):
... match u16 0xPPPP 0xFFFF at -2 match u16 0xM4M5 0xFFFF at -4 match u32
0xM0M1M2M3 0xFFFFFFFF at -8

The below is simplistic but it works to demonstrate the above.

tc qdisc add dev ppp0 root handle 1:0 htb default 20
tc class add dev ppp0 parent 1:0 classid 1:1 htb rate 128kbit ceil 128kbit

tc class add dev ppp0 parent 1:1 classid 1:10 htb rate 64kbit ceil 128kbit tc class add dev ppp0 parent 1:1 classid 1:20 htb rate 64kbit ceil 128kbit

tc qdisc add dev ppp0 parent 1:10 handle 100: sfq perturb 10
tc qdisc add dev ppp0 parent 1:20 handle 200: sfq perturb 10

# My Laptop
tc filter add dev ppp0 parent 1:0 protocol ip prio 1 u32 match u16 0x0800 0xFFFF at -2 match u16 0xM4M5 0xFFFF at -4 match u32 0xM0M1M2M3 0xFFFFFFFF
at -8 flowid 1:10
# My Desktop
tc filter add dev ppp0 parent 1:0 protocol ip prio 1 u32 match u16 0x0800 0xFFFF at -2 match u16 0xM4M5 0xFFFF at -4 match u32 0xM0M1M2M3 0xFFFFFFFF
at -8 flowid 1:20
# change the MAC's of course.

tc -s -d class show dev ppp0
tc -s -d qdisc show dev ppp0
tc -s -d filter show dev ppp0

There you have it.

:L
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--

Regards Mike.

Michael Davidson
Barone Budge & Dominick
Email: michael@xxxxxxxxx
Office: +27 11 532 8380
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