netdev - Re: [iproute2] tc action mirred question

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Date:	Fri, 11 Sep 2009 11:45:10 -0700 (PDT)
From:	Xiaofei Wu <xiaofei_wu08@...oo.com>
To:	hadi@...erus.ca
Cc:	linux netdev <netdev@...r.kernel.org>
Subject: Re: [iproute2] tc action mirred    question

I run your example ( mirror  lo -> eth0) on Sep. 10th, got almost the same result(in my last email) as yours.
I think interface 'lo' is very special.

When I do the following (eth0 -> lo), the results are very strange.
1> run 'tc qdisc add dev eth0 handle 1: root prio'

2>  tc filter add dev eth0 parent 1: protocol ip prio 10 u32 \
match ip src 192.168.1.0/32 flowid 1:16 \
action pedit munge offset -14 u16 set 0x0023 \
munge offset -12 u32 set 0xcdafecda \
munge offset -8 u32 set 0x0023cdaf \
munge offset -4 u32 set 0xd0740800 pipe \
action mirred egress mirror dev lo

window1  run ' ping 192.168.1.1'
window2  'tcpdump -i lo -e', I can not capture any packets.

mirror  lo -> eth0 ok, eth0 -> lo  can not work ???

2'> change 'action mirred egress mirror dev lo' to 'action mirred egress mirror dev eth1' ,
'tcpdump -i eth1 -e'    also capture nothing.
Does this mean something wrong with ' action pedit ...' ?   ("offset must be on 32 bit boundaries"?)

>> lo -> eth0
>> But I want to only modify the dst MAC, src MAC of the mirroring packets, transmit them to next hop. 
>> (not modify the dst,src MAC of the packets to 'lo').  What should I do?

>Ok, so modifying then mirroring wont work on ingress;->
>One thing you can try is first to mirror lo->eth0, then pedit only
>specific flow on eth0 that came from lo.

How to do this. Could you show me the example commands?   Thank you.

regards,
wu

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