Packet capture is a fundamental tool for developing, debugging, and testing networking.
fx sniff is a development host command that:
Wireshark.netdump is a packet capturer with rich capture filter support. fx sniff internally invokes netdump with predefined capture filters that are necessary for Fuchsia's developer workflow. For use cases where fx sniff is not viable (e.g. when you have serial console access but without dev host connected), use netdump directly.
netdump is part of the universe dependency list of the core product. If a package server is available, there is no extra step to prepare the image. Just running netdump will fetch the binary.
If the package server is not available, make sure to bundle netdump into your set of base packages.
$ fx set core.x64 --with-base //src/connectivity/network/netdump $ fx build
[host] $ fx sniff wlan
By default, this command captures packets for 30 seconds. To configure the duration, add the --time {sec} or -t {sec} option.
If you don't know the network interface name, run fx sniff without options. The error message shows you what interfaces are available. Alternatively, run:
[host] $ fx shell net if list # Take note of `filepath` in output
[host] $ fx sniff --view hex eth
[host] $ fx sniff --file my_packets wlan
The captured packets are first stored in the target's /tmp/ directory. After the capture is complete, the files are moved to //out/my_packets.pcapng automatically.
NOTE: Linux only.
[host] $ fx sniff --view wireshark wlan
Packet capture runs for the specified duration (--time or -t option). If a user desires to stop early, presse one of the following keys:
c, q, C, Q
This will stop both a target side process and a host side process.
fx sniff requires working ssh connectivity from the host to the target, which means that networking must be working to some degree. In some cases, networking might not be working at all. If you have access to the serial console while networking, including ssh, is not working, you must run netdump directly on the target. netdump provides a richer set of features than fx sniff.
Before you use netdump, you must get the file path for the network interface. This is an example for WLAN interface (assuming your target device has one and only one WLAN interface - which is a typical case).
[target] $ iface_filepath=$(net if list wlan | grep filepath | while read c1 c2; do echo $c2; done)
[target] $ netdump -t 30 "$iface_filepath"
[target] $ netdump --raw "$iface_filepath"
[target] $ netdump --pcapdump ${iface_filepath}
[target] $ netdump -t 30 -w /tmp/my_packets.pcapng "$iface_filepath"
[host] $ cd ${FUCHSIA_OUT_DIR} && fx scp "[$(fx get-device-addr)]:/tmp/my_precious_packets.pcapng" .
netdump help[target] $ netdump --help
[target] $ netdump -t 10 -f "arp or port dns,dhcp" "$iface_filepath"
The packet filter language syntax is as follows. Keywords are in bold. Optional terms are in [square brackets]. Placeholders for literals are in <angle brackets>. Binary logical operators associate to the left. All keywords and port aliases should be in lower case.
<len>: Packet length in bytes. Greater or less comparison is inclusive of len.<mac_addr>: MAC address, e.g. DE:AD:BE:EF:D0:0D. Hex digits are case-insensitive.<ip_addr>: IP address consistent with the IP version specified previously. E.g. 192.168.1.10, 2001:4860:4860::8888.<port_lst>: List of ports or port ranges separated by commas, e.g. 13,ssh,6000-7000,20. The following aliases for defined ports and port ranges can be used as items in the list, but not as part of a range (3,dhcp,12 is allowed, http-100 is not):| Alias | Port(s) |
|---|---|
dhcp | 67-68 |
dns | 53 |
echo | 7 |
ftpxfer | 20 |
ftpctl | 21 |
http | 80 |
https | 443 |
irc | 194 |
ntp | 123 |
sftp | 115 |
ssh | 22 |
telnet | 23 |
tftp | 69 |
dbglog | Netboot debug log port |
dbgack | Netboot debug log ack port |
The following aliases may be used instead of the keywords listed in the syntax:
| Keyword | Alias |
|---|---|
ip | ip4 |
port | portrange |
fx workflow packet signaturesThere are many different kinds of services running between the Fuchsia development host and the target. Those are usually invoked by fx commands. Most of times, you are not interested in those packets generated by the fx workflows. The following table lists noteworthy signatures.
| Use | Signature | Reference |
|---|---|---|
| Logger | port 33337 | DEBUGLOG_PORT |
| Logger | port 33338 | DEBUGLOG_ACK_PORT |
| Bootserver | port 33330 | NB_SERVER_PORT |
| Bootserver | port 33331 | NB_ADVERT_PORT |
| Bootserver | port 33332 | NB_CMD_PORT_START |
| Bootserver | port 33339 | NB_CMD_PORT_END |
| Bootserver | port 33340 | NB_TFTP_OUTGOING_PORT |
| Bootserver | port 33341 | NB_TFTP_INCOMING_PORT |
| Package Server | port 8083 | docs/packages.md |
| fx shell | port 22 | devshell/shell |
| target netsvc addr | fe80::xxxx:xxff:fexx:xxxx%XX | fx device-finder list --netboot |
| host link-local addr | fe80::xxxx:xxxx:xxxx:xxxx%XX | fx device-finder list --ipv4=false --local |
| target netstack addr | fe80::xxxx:xxxx:xxxx:xxxx%XX | fx get-device-addr |
| zxdb | port 2345 | devshell/contrib/debug |
| - | port 65026 | |
| - | port 65268 | |
| - | 1900 |
netdump is broken?You can run some sanity checks locally.
[host] $ fx set core.x64 --with //src/connectivity:tests,//src/connectivity/network/netdump:netdump_unit_tests # (After running your target) [host] $ fx test netdump_unit_test # unit test [host] $ fx test netdump_integration_tests # integration test
Q fx sniff commands give me the error env: python3: No such file or directory
A Please install Python 3 in your environment. Fuchsia is in the middle of migrating from Python 2.7 to Python 3.
Q I get the error /boot/bin/sh: netdump not found
A The netdump package is not prepared. Make sure to bundle netdump in the image. See prepare the image.