Wireshark mailing list archives
Re: dumpcap and bpf assembler
From: Richard Stearn <richard () rns-stearn demon co uk>
Date: Wed, 27 May 2015 15:47:36 +0100
Hi Sake Thank you for the response. Unfortunately the information I am after filtering on is not in a capture file, it only exists in the kernel at run time, skb->protocol. Hence linking this to dumpcap. As a packet is processed through the network stack the value of skb-protocol changes to reflect the next protocol to be inspected. For example, an AX25 packet is handed to the network interface by the mkiss driver and skb->protocol == ETH_P_AX25. The packet is then processed by the AX25 protocol driver and in the case of the payload being an IP packet skb->protocol is then changed to ETH_P_IP and the packet handed back to the network interface. So now we have apparently the same packet appearing on the network interface for a second time, libpcap can not distinguish between the two as the only difference is the value of skb->protocol, for which there appears to be no way of filtering on skb->protocol without resorting to BPF assembler. I hope I am making sense. -- Regards Richard ___________________________________________________________________________ Sent via: Wireshark-users mailing list <wireshark-users () wireshark org> Archives: https://www.wireshark.org/lists/wireshark-users Unsubscribe: https://wireshark.org/mailman/options/wireshark-users mailto:wireshark-users-request () wireshark org?subject=unsubscribe
Current thread:
- dumpcap and bpf assembler Richard Stearn (May 26)
- Re: dumpcap and bpf assembler Sake Blok (May 27)
- Re: dumpcap and bpf assembler Richard Stearn (May 27)
- Re: dumpcap and bpf assembler Sake Blok (May 27)
- Re: dumpcap and bpf assembler Richard Stearn (May 28)
- Re: dumpcap and bpf assembler Guy Harris (May 28)
- Re: dumpcap and bpf assembler Sake Blok (May 29)
- Re: dumpcap and bpf assembler Richard Stearn (May 27)
- Re: dumpcap and bpf assembler Sake Blok (May 27)