1 Using vpptrace.sh for VPP Packet Tracing
2 ========================================
4 VPP allows tracing of incoming packets using CLI commands ``trace add``
5 and ``show trace`` as explained [here](VPP_PACKET_TRACING_K8S.html), but
6 it is a rather cumbersome process.
8 The buffer for captured packets is limited in size, and once it gets
9 full the tracing stops. The user has to manually clear the buffer
10 content, and then repeat the trace command to resume the packet capture,
11 losing information about all packets received in the meantime.
13 Packet filtering exposed via the CLI command ``trace filter`` is also
14 quite limited in what it can do. Currently there is just one available
15 filter, which allows you to keep only packets that include a certain
16 node in the trace or exclude a certain node in the trace. It is not
17 possible to filter the traffic by its content (e.g., by the
18 source/destination IP address, protocol, etc.).
20 Last but not least, it is not possible to trace packets on a selected
21 interface like ``tcpdump``, which allows tracing via the option ``-i``.
22 VPP is only able to capture packets on the *RX side* of selected
23 *devices* (e.g., dpdk, virtio, af-packet). This means that interfaces
24 based on the same device cannot be traced for incoming packets
25 individually, but only all at the same time. In Contiv/VPP all pods are
26 connected with VPP via the same kind of the TAP interface, meaning that
27 it is not possible to capture packets incoming only from one selected
30 Contiv/VPP ships with a simple bash script
31 `vpptrace.sh <https://github.com/contiv/vpp/blob/master/scripts/vpptrace.sh>`__,
32 which helps alleviate the aforementioned VPP limitations. The script
33 automatically re-initializes buffers and traces whenever it is close to
34 getting full, in order to avoid packet loss as much as possible. Next it
35 allows you to filter packets by the content of the trace. There are two
36 modes of filtering: - *substring mode* (default): packet trace must
37 contain a given sub-string in order to be included in the output -
38 *regex mode*: packet trace must match a given regex in order to be
41 The script is still limited, in that capture runs only on the RX side of
42 all interfaces that are built on top of selected devices. Using
43 filtering, however, it is possible to limit *traffic by interface*
44 simply by using the interface name as a substring to match against.
49 Run the script with option ``-h`` to get the usage printed:
53 Usage: ./vpptrace.sh [-i <VPP-IF-TYPE>]... [-a <VPP-ADDRESS>] [-r] [-f <REGEXP> / <SUBSTRING>]
54 -i <VPP-IF-TYPE> : VPP interface *type* to run the packet capture on (e.g., dpdk-input, virtio-input, etc.)
56 - af-packet-input: afpacket, af-packet, veth
57 - virtio-input: tap (version determined from the VPP runtime config), tap2, tapv2
58 - tapcli-rx: tap (version determined from the VPP config), tap1, tapv1
59 - dpdk-input: dpdk, gbe, phys*
60 - multiple interfaces can be watched at the same time - the option can be repeated with
62 - default = dpdk + tap
63 -a <VPP-ADDRESS> : IP address or hostname of the VPP to capture packets from
64 - not supported if VPP listens on a UNIX domain socket
66 -r : apply filter string (passed with -f) as a regexp expression
67 - by default the filter is NOT treated as regexp
68 -f : filter string that packet must contain (without -r) or match as regexp (with -r) to be printed
69 - default is no filtering
71 ``VPP-IF-TYPE`` is a repeated option used to select the set of devices
72 (e.g., virtio, dpdk, etc.) to capture the incoming traffic. Script
73 provides multiple aliases, which are much easier to remember than the
74 device names. For ``dpdk-input`` one can enter just ``dpdk``, or
75 anything starting with ``phys``, etc. For TAPs, the script is even smart
76 enough to find out the TAP version used, which allows to enter just
77 ``tap`` as the device name.
79 If ``VPP-IF-TYPE`` is not specified, then the default behaviour is to
80 capture from both ``dpdk`` (traffic entering the node from outside) and
81 ``tap`` (preferred interface type for pod-VPP and host-VPP
82 interconnection, receiving node-initiated traffic).
84 vpptrace.sh can capture packets even from a VPP on a different host,
85 provided that VPP-CLI listens on a port, and not on a UNIX domain socket
86 (for security reasons IPC is the default communication link, see
87 ``/etc/vpp/contiv-vswitch.conf``). Enter the destination node IP address
88 via the option ``-a``\ (localhost is the default).
90 The capture can be filtered via the ``-f`` option. The output will
91 include only packets whose trace matches contain the given
92 expression/sub-string.
94 Option ``-r`` enables the regex mode for filtering.
99 - Capture all packets entering VPP via ``tapcli-1`` interface **AND**
100 all packets leaving VPP via ``tapcli-1`` that were sent from a pod,
101 or the host on the *same node* (sent from tap, not Gbe):
105 $ vpptrace.sh -i tap -f "tapcli-1"
107 \ 2 - Capture all packets with source or destination IP address 10.1.1.3:
111 $ vpptrace.sh -i tap -i dpdk -f "10.1.1.3"
114 $ vpptrace.sh "10.1.1.3"
116 - Capture all SYN-ACKs received from outside:
120 $ vpptrace.sh -i dpdk -f "SYN-ACK"