tcpdump mailing list archives
Re: Multiple Needles in Multiple Haystacks.
From: Guy Harris <guy () alum mit edu>
Date: Thu, 17 Nov 2016 16:43:44 -0800
On Nov 17, 2016, at 7:29 AM, Zaphod Beeblebrox <zbeeble () gmail com> wrote:
Fundamental to my problem is filtering the PPP inside L2TP. Making this complex, the L2TP speakers I'm dealing with don't deliver at the same offsets.
...and libpcap's filter-to-BPF compiler doesn't have a "check for L2TP and, if you find it, make all filter tests after the match test the packet *inside* the L2TP packet" expression, the way it has for PPPoE, for example. I'll see if I can spend some time looking at that.
Something like "ppp[0:2] == 0x8021" should pull out the IPCP. Or is that ppp[2:2] ... but neither works. Some other reading that's hard to find would suggest something like "protochain l2tp and ppp proto 0x8021" ... but that doesn't work either.
That's because "protochain" only works for IPv4 and IPv6. _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- Multiple Needles in Multiple Haystacks. Zaphod Beeblebrox (Nov 17)
- Re: Multiple Needles in Multiple Haystacks. Michael Richardson (Nov 17)
- Re: Multiple Needles in Multiple Haystacks. Guy Harris (Nov 17)