tcpdump mailing list archives
Re: Patch to add DLT_AX25 handling to libpcap
From: Richard Stearn <richard () rns-stearn demon co uk>
Date: Tue, 03 Apr 2007 22:57:14 +0100
Guy Harris wrote:
Richard Stearn wrote:Adding DLT_AX25_KISS is the obvious way to go with the exception that Linuxidentifies AX.25 in KISS packets as DLT_AX25 (protocol 3)."Identifies" in what sense?
As in returns 3 as an identifier of the protocol type.
I don't see any use of DLT_AX25 in the 2.6.20.4 kernel. It appears to use ARPHRD_AX25 as the arphrd value for AX.25 adapters, and that happens to have the same value as DLT_AX25 because the first few DLT_ values were ARP hardware type values, but libpcap doesn't expose ARPHRD_ values to applications - it maps them to DLT_ values.
Fine, same value different meaning.
pcap-linux.c could map ARPHRD_AX25 to DLT_AX25_KISS, which means AX.25 captures done on Linux will have a file type of DLT_AX25_KISS.
As in: declare DLT_AX25_KISS as X and change: pcap-linux.c 1140 case ARPHRD_AX25: 1141 handle->linktype = DLT_AX25; 1142 break; to pcap-linux.c 1140 case ARPHRD_AX25: 1141 handle->linktype = DLT_AX25_KISS; 1142 break; That would be good, tells higher levels exactly what the packet is. To date I have found AX.25 encapsulated in three ways: AX.25 in UDP & TCP - pure AX.25 AX.25 as passed from the MKISS driver with a 1 byte header AX.25 in ethernet (BPQ) with a 2 byte header so your point about dissecting pure AX.25 was well made and DLT_AX25_BPQ may be needed as well. The AX.25 in ethernet (BPQ) uses an ethertype of 0x08ff, probably unregistered. I need to look a lot more closely at the AX.25 protocol driver in Linux. Thanks for your patience. -- Regards Richard - This is the tcpdump-workers list. Visit https://cod.sandelman.ca/ to unsubscribe.
Current thread:
- Re: Patch to add DLT_AX25 handling to libpcap Guy Harris (Apr 01)
- Re: Patch to add DLT_AX25 handling to libpcap Richard Stearn (Apr 01)
- Re: Patch to add DLT_AX25 handling to libpcap Guy Harris (Apr 01)
- Re: Patch to add DLT_AX25 handling to libpcap Guy Harris (Apr 01)
- Re: Patch to add DLT_AX25 handling to libpcap Richard Stearn (Apr 01)
- Re: Patch to add DLT_AX25 handling to libpcap Guy Harris (Apr 03)
- Re: Patch to add DLT_AX25 handling to libpcap Richard Stearn (Apr 03)
- Re: Patch to add DLT_AX25 handling to libpcap Guy Harris (Apr 01)
- Re: Patch to add DLT_AX25 handling to libpcap Richard Stearn (Apr 01)