tcpdump mailing list archives
Re: BPF Extended: addressing BPF's shortcomings
From: Darren Reed <darrenr () netbsd org>
Date: Thu, 11 Jun 2015 20:12:00 +1000
On 11/06/2015 1:08 AM, Paul "LeoNerd" Evans wrote:
On Wed, 10 Jun 2015 23:17:20 +1000 Darren Reed <darrenr () netbsd org> wrote:BPF & IPv6 ---------- The problem with IPv6 and BPF is that the transport header (TCP, UDP, etc) can have a number of extension headers between it and the network header that is present for IPv6. There's no hints in the IPv6 header as to how many of these extension headers there are, or how many bytes the extension header(s) take up. This leaves BPF in a precarious situation because it cannot be reliably used to match on layer 4 packets. What's missing is the ability to either find a specific header after the IPv6 network header or just to determine what the last one is.... If you're considering extending BPF to better suit IPv6, have you seen either of my proposed ideas? 1) Add a LOOP instruction that allows certain kinds of backward-directed jumps, in order to efficiently implement the IPv6 header-chain walking without needing manual loop unrolling, while still giving static guarantees about eventual termination of the program.
I haven't seen much of an appetite for any sort of loop construct in any of the changes or discussions around BPF. Anywhere. It is often brought up but always the point of a BPF program being easily verified is mentioned.
2) A few more AD constants added to the Linux "auxdata" area, giving information about the transport layer.
Can you please expand on this? Darren _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- BPF Extended: addressing BPF's shortcomings Darren Reed (Jun 10)
- Re: BPF Extended: addressing BPF's shortcomings Paul "LeoNerd" Evans (Jun 10)
- Re: BPF Extended: addressing BPF's shortcomings Darren Reed (Jun 11)
- Re: BPF Extended: addressing BPF's shortcomings Paul "LeoNerd" Evans (Jun 11)
- Re: BPF Extended: addressing BPF's shortcomings Michael Richardson (Jun 11)
- Re: BPF Extended: addressing BPF's shortcomings Darren Reed (Jun 11)
- Re: BPF Extended: addressing BPF's shortcomings Paul "LeoNerd" Evans (Jun 10)
- Re: BPF Extended: addressing BPF's shortcomings Mindaugas Rasiukevicius (Jun 10)
- Re: BPF Extended: addressing BPF's shortcomings Guy Harris (Jun 10)
- Re: BPF Extended: addressing BPF's shortcomings Paul "LeoNerd" Evans (Jun 11)
- Re: BPF Extended: addressing BPF's shortcomings Darren Reed (Jun 11)
- Re: BPF Extended: addressing BPF's shortcomings Paul "LeoNerd" Evans (Jun 11)
- Re: BPF Extended: addressing BPF's shortcomings Guy Harris (Jun 10)