#+EXPORT_FILE_NAME: xdpdump
#+TITLE: xdpdump
#+MAN_CLASS_OPTIONS: :section-id "8\" \"DATE\" \"VERSION\" \"a simple tcpdump like tool for capturing packets at the XDP layer"
# This file serves both as a README on github, and as the source for the man
# page; the latter through the org-mode man page export support.
# .
# To export the man page, simply use the org-mode exporter; (require 'ox-man) if
# it's not available.
# .
# The org-mode export doesn't support extended title lines, so manually copy
# over the first line of the resulting .man file before exporting and
# committing.

* xdpdump - a simple tcpdump like tool for capturing packets at the XDP layer
=xdpdump= is a simple XDP packet capture tool that tries to behave similar to
=tcpdump=, however, it has no packet filter or decode capabilities.

This can be used for debugging XDP programs that are already loaded on an
interface.  Packets can be dumped/inspected before on *entry* to XDP program,
or after at *exit* from an XDP program.  Furthermore, at *exit* the XDP
action is also captured.  This means that even packets that are dropped at the
XDP layer can be captured via this tool.

=xdpdump= works by attaching a bpf trace program to the XDP entry and/or exit
function which stores the raw packet in a perf trace buffer. If no XDP program
is loaded this approach can not be used and the tool will use a libpcap
live-capture to be backward compatible.

** Running xdpdump
The syntax for running =xdpdump= is:

#+begin_src
Usage: xdpdump [options]

 XDPDump tool to dump network traffic

Options:
     --rx-capture <mode>    Capture point for the rx direction (valid values: entry,exit)
 -D, --list-interfaces      Print the list of available interfaces
 -i, --interface <ifname>   Name of interface to capture on
     --perf-wakeup <events>  Wake up xdpdump every <events> packets
 -p, --program-names <prog>  Specific program to attach to
 -s, --snapshot-length <snaplen>  Minimum bytes of packet to capture
     --use-pcap             Use legacy pcap format for XDP traces
 -w, --write <file>         Write raw packets to pcap file
 -x, --hex                  Print the full packet in hex
 -v, --verbose              Enable verbose logging (-vv: more verbose)
     --version              Display version information
 -h, --help                 Show this help
#+end_src

* The options explained
The =xdpdump= tool tries to mimic the basic =tcpdump= options, but just in case
below each of the available options is explained:

** --rx-capture <mode>
Specify where the ingress packet gets captured. Either at the entry of the XDP
program and/or exit of the XDP program. Valid options are *entry*, *exit*,
or both *entry,exit*. The packet at *exit* can be modified by the XDP
program. If you are interested to see both the original and modified packet,
use the *entry,exit* option. With this, each packet is captured twice. The
default value for this is *entry*.
** -D, --list-interfaces
Display a list of available interfaces and any XDP program loaded
** -i, --interface <ifname>
Listen on interface =ifname=. Note that if no XDP program is loaded on the
interface it will use libpcap's live capture mode to capture the packets.
** --perf-wakeup <events>                                     :feat_perfbuf:
Let the Kernel wake up =xdpdump= once for every =<events>= being posted in the
perf ring buffer. The higher the number the less the impact is on the actual
XDP program. The default value is 0, which automatically calculates the
value based on the available CPUs/buffers. Use -v to see the actual used value.
** -p, --program-names <prog>
The Linux API does not provide the full name of the attached eBPF entry function
if it's longer than 15 characters. xdpdump will try to guess the correct
function name from the available BTF debug information. However, if multiple
functions exist with the same leading name, it can not pick the correct one. It
will dump the available functions, and you can choose the correct one, and
supply it with this option.
** -P, --promiscuous-mode
This option puts the interface into promiscuous mode.
** -s, --snapshot-length <snaplen>
Capture *snaplen* bytes of a packet rather than the default 262144 bytes.
** --use-pcap
Use legacy pcap format for XDP traces. By default, it will use the PcapNG format
so that it can store various metadata.
** -w, --write <file>
Write the raw packets to a pcap file rather than printing them out hexadecimal. Standard output is used if *file* is =-=.
** -x, --hex
When dumping packets on the console also print the full packet content in hex.
** -v, --verbose
Enable debug logging. Specify twice for even more verbosity.
** --version
Display =xpdump= version information and exit.
** -h, --help
Display a summary of the available options

* Examples
The below will load the =xdp-filter= program on eth0, but it does not do any
actual filtering:

#+begin_src
# xdp-filter load --mode skb eth0
#
# xdpdump -D
if_index  if_name           XDP program entry function
--------  ----------------  --------------------------------------------------
1         lo                <No XDP program loaded!>
2         eth0              xdpfilt_dny_all()
#+end_src

Now we can try =xdpdump=:

#+begin_src
# xdpdump -i eth0 -x
listening on eth0, ingress XDP program xdpfilt_dny_all, capture mode entry, capture size 262144 bytes
1584373839.460733895: packet size 102 bytes, captured 102 bytes on if_index 2, rx queue 0, @entry
  0x0000:  52 54 00 db 44 b6 52 54 00 34 38 da 08 00 45 48  RT..D.RT.48...EH
  0x0010:  00 58 d7 dd 40 00 40 06 ec c3 c0 a8 7a 01 c0 a8  .X..@.@.....z...
  0x0020:  7a 64 9c de 00 16 0d d5 c6 bc 46 c9 bb 11 80 18  zd........F.....
  0x0030:  01 f5 7b b4 00 00 01 01 08 0a 77 0a 8c b8 40 12  ..{.......w...@.
  0x0040:  cc a6 00 00 00 10 54 ce 6e 20 c3 e7 da 6c 08 42  ......T.n ...l.B
  0x0050:  d6 d9 ee 42 42 f0 82 c9 4f 12 ed 7b 19 ab 22 0d  ...BB...O..{..".
  0x0060:  09 29 a9 ee df 89                                .)....

1584373839.462340808: packet size 66 bytes, captured 66 bytes on if_index 2, rx queue 0, @entry
  0x0000:  52 54 00 db 44 b6 52 54 00 34 38 da 08 00 45 48  RT..D.RT.48...EH
  0x0010:  00 34 d7 de 40 00 40 06 ec e6 c0 a8 7a 01 c0 a8  .4..@.@.....z...
  0x0020:  7a 64 9c de 00 16 0d d5 c6 e0 46 c9 bc 85 80 10  zd........F.....
  0x0030:  01 f5 74 0c 00 00 01 01 08 0a 77 0a 8c ba 40 12  ..t.......w...@.
  0x0040:  d2 34                                            .4
^C
2 packets captured
0 packets dropped by perf ring
#+end_src

Below are two more examples redirecting the capture file to =tcpdump= or
=tshark=:

#+begin_src
# xdpdump -i eth0 -w - | tcpdump -r - -n
listening on eth0, ingress XDP program xdpfilt_dny_all, capture mode entry, capture size 262144 bytes
reading from file -, link-type EN10MB (Ethernet)
15:55:09.075887 IP 192.168.122.1.40928 > 192.168.122.100.ssh: Flags [P.], seq 3857553815:3857553851, ack 3306438882, win 501, options [nop,nop,TS val 1997449167 ecr 1075234328], length 36
15:55:09.077756 IP 192.168.122.1.40928 > 192.168.122.100.ssh: Flags [.], ack 37, win 501, options [nop,nop,TS val 1997449169 ecr 1075244363], length 0
15:55:09.750230 IP 192.168.122.1.40928 > 192.168.122.100.ssh: Flags [P.], seq 36:72, ack 37, win 501, options [nop,nop,TS val 1997449842 ecr 1075244363], length 36
#+end_src

#+begin_src
# xdpdump -i eth0 -w - | tshark -r - -n
listening on eth0, ingress XDP program xdpfilt_dny_all, capture mode entry, capture size 262144 bytes
    1   0.000000 192.168.122.1 → 192.168.122.100 SSH 102 Client: Encrypted packet (len=36)
    2   0.000646 192.168.122.1 → 192.168.122.100 TCP 66 40158 → 22 [ACK] Seq=37 Ack=37 Win=1467 Len=0 TSval=1997621571 TSecr=1075416765
    3  12.218164 192.168.122.1 → 192.168.122.100 SSH 102 Client: Encrypted packet (len=36)
#+end_src

* BUGS
Please report any bugs on Github: https://github.com/xdp-project/xdp-tools/issues

* AUTHOR

=xdpdump= was written by Eelco Chaudron
