1xdpdump(a8)simple tcpdump like tool for capturing packets at the XDP laxydeprdump(8)
2
6 xdpdump is a simple XDP packet capture tool that tries to behave simi‐
7 lar to tcpdump, however, it has no packet filter or decode capabili‐
8 ties.
9 This can be used for debugging XDP programs that are already loaded on
12 an interface. Packets can be dumped/inspected before on entry to XDP
13 program, or after at exit from an XDP program. Furthermore, at exit
14 the XDP action is also captured. This means that even packets that are
15 dropped at the XDP layer can be captured via this tool.
16 xdpdump works by attaching a bpf trace program to the XDP entry and/or
19 exit function which stores the raw packet in a perf trace buffer. If no
20 XDP program is loaded this approach can not be used and the tool will
21 use a libpcap live-capture to be backward compatible.
22 Running xdpdump
25 The syntax for running xdpdump is:
26 Usage: xdpdump [options]
28 XDPDump tool to dump network traffic
30 Options:
32 --rx-capture <mode> Capture point for the rx direction (valid values: entry,exit)
33 -D, --list-interfaces Print the list of available interfaces
34 -i, --interface <ifname> Name of interface to capture on
35 --perf-wakeup <events> Wake up xdpdump every <events> packets
36 -p, --program-names <prog> Specific program to attach to
37 -s, --snapshot-length <snaplen> Minimum bytes of packet to capture
38 --use-pcap Use legacy pcap format for XDP traces
39 -w, --write <file> Write raw packets to pcap file
40 -x, --hex Print the full packet in hex
41 -v, --verbose Enable verbose logging (-vv: more verbose)
42 --v1.2.0 Display v1.2.0 information
43 -h, --help Show this help
44
47 The xdpdump tool tries to mimic the basic tcpdump options, but just in
48 case below each of the available options is explained:
49 --rx-capture <mode>
52 Specify where the ingress packet gets captured. Either at the entry of
53 the XDP program and/or exit of the XDP program. Valid options are en‐
54 try, exit, or both entry,exit. The packet at exit can be modified by
55 the XDP program. If you are interested to see both the original and
56 modified packet, use the entry,exit option. With this, each packet is
57 captured twice. The default value for this is entry.
58 -D, --list-interfaces
60 Display a list of available interfaces and any XDP program loaded
61 --load-xdp-mode
63 Specifies which loader mode to use with the --load-xdp-program option.
64 The valid values are ‘native’, which is the default in-driver XDP mode,
65 ‘skb’, which causes the so-called skb mode (also known as generic XDP)
66 to be used, ‘hw’ which causes the program to be offloaded to the hard‐
67 ware, or ‘unspecified’ which leaves it up to the kernel to pick a mode
68 (which it will do by picking native mode if the driver supports it, or
69 generic mode otherwise). Note that using ‘unspecified’ can make it dif‐
70 ficult to predict what mode a program will end up being loaded in. For
71 this reason, the default is ‘native’.
72 --load-xdp-program
74 If no XDP program is loaded on the interface, by default, xdpdump will
75 fallback to libpcap's live capture mode to capture the packets. Alter‐
76 natively, with this option, you can ask xdpdump to load an XDP program
77 to capture the packets directly.
78 -i, --interface <ifname>
80 Listen on interface ifname. Note that if no XDP program is loaded on
81 the interface it will use libpcap's live capture mode to capture the
82 packets.
83 --perf-wakeup <events>
85 Let the Kernel wake up xdpdump once for every <events> being posted in
86 the perf ring buffer. The higher the number the less the impact is on
87 the actual XDP program. The default value is 0, which automatically
88 calculates the value based on the available CPUs/buffers. Use -v to see
89 the actual used value.
90 -p, --program-names [<prog>|all]
92 This option allows you to capture packets for a specific, set of, or
93 all XDP programs loaded on the interface. You can either specify the
94 actual program names or program IDs separated by commas. In the case
95 where multiple programs are attached with the same name, you should use
96 the program ID. Use the -D option to see the loaded programs and their
97 IDs.
98 In addition, the Linux API does not provide the full name of the at‐
102 tached eBPF entry function if it's longer than 15 characters. xdpdump
103 will try to guess the correct function name from the available BTF de‐
104 bug information. However, if multiple functions exist with the same
105 leading name, it can not pick the correct one. It will dump the avail‐
106 able functions, and you can choose the correct one, and supply it with
107 this option. If you have programs with duplicate long names, you also
108 need to specify the program ID with the full name. This can be done by
109 adding the id to the name with the @<id> suffix.
110 -P, --promiscuous-mode
112 This option puts the interface into promiscuous mode.
113 -s, --snapshot-length <snaplen>
115 Capture snaplen bytes of a packet rather than the default 262144 bytes.
116 --use-pcap
118 Use legacy pcap format for XDP traces. By default, it will use the
119 PcapNG format so that it can store various metadata.
120 -w, --write <file>
122 Write the raw packets to a pcap file rather than printing them out
123 hexadecimal. Standard output is used if file is -.
124 -x, --hex
126 When dumping packets on the console also print the full packet content
127 in hex.
128 -v, --verbose
130 Enable debug logging. Specify twice for even more verbosity.
131 --v1.2.0
133 Display xpdump v1.2.0 information and exit.
134 -h, --help
136 Display a summary of the available options
137
140 The below will load the xdp-filter program on eth0, but it does not do
141 any actual filtering:
142 # xdp-filter load --mode skb eth0
144 #
145 # xdpdump -D
146 Interface Prio Program name Mode ID Tag Chain actions
147 --------------------------------------------------------------------------------------
148 lo <No XDP program loaded!>
149 eth0 xdp_dispatcher skb 10651 d51e469e988d81da
150 => 10 xdpfilt_alw_all 10669 0b394f43ab24501c XDP_PASS
151 Now we can try xdpdump:
154 # xdpdump -i eth0 -x
156 listening on eth0, ingress XDP program ID 10651 func xdp_dispatcher, capture mode entry, capture size 262144 bytes
157 1584373839.460733895: xdp_dispatcher()@entry: packet size 102 bytes, captured 102 bytes on if_index 2, rx queue 0, id 1
158 0x0000: 52 54 00 db 44 b6 52 54 00 34 38 da 08 00 45 48 RT..D.RT.48...EH
159 0x0010: 00 58 d7 dd 40 00 40 06 ec c3 c0 a8 7a 01 c0 a8 .X..@.@.....z...
160 0x0020: 7a 64 9c de 00 16 0d d5 c6 bc 46 c9 bb 11 80 18 zd........F.....
161 0x0030: 01 f5 7b b4 00 00 01 01 08 0a 77 0a 8c b8 40 12 ..{.......w...@.
162 0x0040: cc a6 00 00 00 10 54 ce 6e 20 c3 e7 da 6c 08 42 ......T.n ...l.B
163 0x0050: d6 d9 ee 42 42 f0 82 c9 4f 12 ed 7b 19 ab 22 0d ...BB...O..{..".
164 0x0060: 09 29 a9 ee df 89 .)....
165 1584373839.462340808: xdp_dispatcher()@entry: packet size 66 bytes, captured 66 bytes on if_index 2, rx queue 0, id 2
167 0x0000: 52 54 00 db 44 b6 52 54 00 34 38 da 08 00 45 48 RT..D.RT.48...EH
168 0x0010: 00 34 d7 de 40 00 40 06 ec e6 c0 a8 7a 01 c0 a8 .4..@.@.....z...
169 0x0020: 7a 64 9c de 00 16 0d d5 c6 e0 46 c9 bc 85 80 10 zd........F.....
170 0x0030: 01 f5 74 0c 00 00 01 01 08 0a 77 0a 8c ba 40 12 ..t.......w...@.
171 0x0040: d2 34 .4
172 ^C
173 2 packets captured
174 0 packets dropped by perf ring
175 Below are two more examples redirecting the capture file to tcpdump or
178 tshark:
179 # xdpdump -i eth0 -w - | tcpdump -r - -n
181 listening on eth0, ingress XDP program ID 10651 func xdp_dispatcher, capture mode entry, capture size 262144 bytes
182 reading from file -, link-type EN10MB (Ethernet)
183 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
184 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
185 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
186 # xdpdump -i eth0 -w - | tshark -r - -n
188 listening on eth0, ingress XDP program ID 10651 func xdp_dispatcher, capture mode entry, capture size 262144 bytes
189 1 0.000000 192.168.122.1 → 192.168.122.100 SSH 102 Client: Encrypted packet (len=36)
190 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
191 3 12.218164 192.168.122.1 → 192.168.122.100 SSH 102 Client: Encrypted packet (len=36)
192 One final example capturing specific XDP programs loaded on the inter‐
195 face:
196 # xdpdump -D
198 Interface Prio Program name Mode ID Tag Chain actions
199 --------------------------------------------------------------------------------------
200 lo <No XDP program loaded!>
201 eth0 xdp_dispatcher skb 10558 d51e469e988d81da
202 => 5 xdp_test_prog_w 10576 b5a46c6e9935298c XDP_PASS
203 => 10 xdp_pass 10582 3b185187f1855c4c XDP_PASS
204 => 10 xdp_pass 10587 3b185187f1855c4c XDP_PASS
205 We would like to see the packets on the xdp_dispatcher() and the 2nd
208 xdp_pass() program:
209 # xdpdump -i eth0 --rx-capture=entry,exit -p xdp_dispatcher,xdp_pass@10587
211 or
212 # xdpdump -i eth0 --rx-capture=entry,exit -p 10558,10587
213 listening on eth0, ingress XDP program ID 10558 func xdp_dispatcher, ID 10587 func xdp_pass, capture mode entry/exit, capture size 262144 bytes
214 1607694215.501287259: xdp_dispatcher()@entry: packet size 102 bytes on if_index 2, rx queue 0, id 1
215 1607694215.501371504: xdp_pass()@entry: packet size 102 bytes on if_index 2, rx queue 0, id 1
216 1607694215.501383099: xdp_pass()@exit[PASS]: packet size 102 bytes on if_index 2, rx queue 0, id 1
217 1607694215.501394709: xdp_dispatcher()@exit[PASS]: packet size 102 bytes on if_index 2, rx queue 0, id 1
218 ^C
219 4 packets captured
220 0 packets dropped by perf ring
221
224 Please report any bugs on Github: https://github.com/xdp-project/xdp-
225 tools/issues
226
229 xdpdump was written by Eelco Chaudron
230V1.2.0 JULY 24, 2021 xdpdump(8)