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

Linux Advanced Routing and Traffic Control

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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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