tcpdump mailing list archives
Re: Adding loopback adapter detection for Windows
From: Guy Harris <guy () alum mit edu>
Date: Sun, 24 Jan 2016 11:04:09 -0800
On Jan 24, 2016, at 6:46 AM, Yang Luo <hsluoyb () gmail com> wrote:
I have implemented a loopback adapter called "Npcap Loopback Adapter" on Windows. It's like lo in linux. I know that libpcap recognizes "lo" by just matching the adapter name with "lo".
...*if* the OS doesn't helpfully provide, as one of the interface flags, IFF_LOOPBACK: $ ifconfig lo0 lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> mtu 16384 ^^^^^^^^ options=3<RXCSUM,TXCSUM> inet6 ::1 prefixlen 128 inet 127.0.0.1 netmask 0xff000000 inet6 fe80::1%lo0 prefixlen 64 scopeid 0x1 nd6 options=1<PERFORMNUD> which is also provided by other BSD-flavored interfaces and, at least with newer kernels, Linux, and possibly other OSes. If the flag *isn't* specified, it checks whether the name is either "lo" or "lo" followed by a single digit.
So possible solutions are: 1) Adding registry read code to libpcap, read the name of "Npcap Loopback Adapter" and compare it with the value in the code. 2) Call my provided PacketIsLoopbackAdapter. Unfortunately, as my Npcap is not a official successor of WinPcap. I can't expect anyone can statically compile against my added PacketIsLoopbackAdapter function. Maybe dynamically function load is needed (LoadLibrary and GetProcAddress). 3) .. Currently my way is like 2), except that I directly built libpcap against my new function. My modification is: https://github.com/nmap/npcap/commit/d18318c495578887829fce8cb366770d3b3c7616 I'm not sure which is the best practice to let libpcap recognize my adapter. Any opinions? Thanks!
On Windows, libpcap and packet.dll are somewhat tied together, in that there's no expectation or requirement that an arbitrary binary version of libpcap code will work with an arbitrary binary version of packet.dll. Normally, the libpcap code and packet.dll are distributed together in a single package; the binary interface that's kept stable is the libpcap ABI (which is also kept stable on UN*Xes), *not* the packet.dll interface. So if you're going to distribute an NPcap that's binary-compatible with WinPcap (possibly adding new APIs, and possibly enhancing old APIs, but not removing old APIs or changing them in an incompatible fashion), you could modify pcap-win32.c etc. as necessary. Please contribute those changes back to libpcap; it might be possible to have the CMake scripts for libpcap check whether packet.dll supports particular APIs and #ifdef out the code that uses those APIs if it's not present. _______________________________________________ tcpdump-workers mailing list tcpdump-workers () lists tcpdump org https://lists.sandelman.ca/mailman/listinfo/tcpdump-workers
Current thread:
- Adding loopback adapter detection for Windows Yang Luo (Jan 24)
- Re: Adding loopback adapter detection for Windows Yang Luo (Jan 24)
- Re: Adding loopback adapter detection for Windows Guy Harris (Jan 24)
- Re: Adding loopback adapter detection for Windows Yang Luo (Jan 24)
- Re: Adding loopback adapter detection for Windows Guy Harris (Jan 24)
- Re: Adding loopback adapter detection for Windows Guy Harris (Jan 24)
- Re: Adding loopback adapter detection for Windows Yang Luo (Jan 25)
- Re: Adding loopback adapter detection for Windows Gisle Vanem (Jan 25)
- Message not available
- Re: Adding loopback adapter detection for Windows Gisle Vanem (Jan 25)
- Re: Adding loopback adapter detection for Windows Yang Luo (Jan 25)
- Re: Adding loopback adapter detection for Windows Yang Luo (Jan 24)
- Message not available
- Re: Adding loopback adapter detection for Windows Guy Harris (Jan 25)
- Re: Adding loopback adapter detection for Windows Yang Luo (Jan 25)