Skip to content

VPP How_To_Use_The_Packet_Generator_and_Packet_Tracer

Jump to bottom
Dave Wallace edited this page Apr 21, 2026 · 1 revision

Contents

Introduction

The VPP platform includes packet generation and packet tracing facilities.

The following example shows steps that you might typically use to run a debug version of the vpp executable file, generate packets, and to analyze results.

Example with IP4 ARP Messages

In the following steps, the VPP executable does not need to be started with superuser permissions. The VPP executable will not discover physical devices when run as a normal user.

Step 1. Start a debug version of vpp

From the command line, make the VPP source directory the working directory and run VPP as shown in the following example.

In the following example, including the dpdk argument means that no physical interfaces will be discovered.

$ ./build-root/install-vpp_debug-native/vpp/bin/vpp unix interactive plugins { plugin dpdk_plugin.so { disable } }

Step 2. Execute the arp4 setup script

From the vpp debug command-line, execute the arp4 script.

DBGvpp# exec src/scripts/vnet/arp4

Step 3. Examine the setup script

Let's tale a look at the contents of the setup script that you just executed. The script .../vpp/vnet/etc/scripts/arp4 contains:

packet-generator new {
  name x
  limit 1
  node ip4-input
  size 64-64
  no-recycle
  data {
    ICMP: 1.0.0.2 -> 2.0.0.2
    ICMP echo_request
    incrementing 100
  }
}

trace add pg-input 100
loop create
loop create
set int state loop0 up
set int state loop1 up

set int ip address loop0 1.0.0.1/24
set int ip address loop1 2.0.0.1/24

The first stanza creates a packet generator stream called "x" which sends a single ipv4 icmp echo-request when enabled. The trace add command arranges to trace 100 packets originating at the pg-input graph node. If you want to trace packets originating at the "ethernet-input" node - which is probably the most typical real-world use-case - make the substitution for that graph node.

Finally, the script configures a couple of loopback interfaces; primarily, so that ip4-input / ip4-lookup won't immediately ditch the generated packet.

Step 4. Generate packets

On the vpp debug command-line, enable the packet generator.

DBGvpp# packet-generator enable

Step 5. Run the packet tracer

Use the show trace command to run the packet tracer.

DBGvpp# show trace
------------------- Start of thread 0 vpp_main -------------------
Packet 1

00:00:21:923147: pg-input
  stream x, 64 bytes, sw_if_index 1
  current data 0, length 64, buffer-pool 0, ref-count 1, trace handle 0x0
  ICMP: 1.0.0.2 -> 2.0.0.2
    tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
    fragment id 0x0000
  ICMP echo_request checksum 0x7a6e id 1
00:00:21:923216: ip4-input
  ICMP: 1.0.0.2 -> 2.0.0.2
    tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
    fragment id 0x0000
  ICMP echo_request checksum 0x7a6e id 1
00:00:21:923252: ip4-not-enabled
    ICMP: 1.0.0.2 -> 2.0.0.2
      tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
      fragment id 0x0000
    ICMP echo_request checksum 0x7a6e id 1
00:00:21:923261: error-drop
  rx:pg0
00:00:21:923270: drop
  null-node: blackholed packets

Step 6. Analyze the information

You can see in the trace above that the packet goes through "ip4-not-enabled" before being dropped. This is because the interface used to inject the packet (pg0 by default) has no IPv4 configuration and hence ARP is not enabled.

Inspecting the error counters you see what we might expect in light of the packet tracer output:

DBGvpp# sh err
   Count                  Node                              Reason               Severity
         1             null-node                      blackholed packets           error

You can enable IPv4 on pg0 by configuring it as eg. unnumbered:

DBGvpp# set int unnumbered pg0 use loop0

And look at the result when re-injecting the packet:

DBGvpp# clear trace
DBGvpp# trace add pg-input 10
DBGvpp# packet-generator enable-stream
DBGvpp# show trace
------------------- Start of thread 0 vpp_main -------------------
Packet 1

00:05:44:786471: pg-input
  stream x, 64 bytes, sw_if_index 1
  current data 0, length 64, buffer-pool 0, ref-count 1, trace handle 0x0
  ICMP: 1.0.0.2 -> 2.0.0.2
    tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
    fragment id 0x0000
  ICMP echo_request checksum 0x7a6e id 1
00:05:44:786501: ip4-input
  ICMP: 1.0.0.2 -> 2.0.0.2
    tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
    fragment id 0x0000
  ICMP echo_request checksum 0x7a6e id 1
00:05:44:786513: ip4-lookup
  fib 0 dpo-idx 3 flow hash: 0x00000000
  ICMP: 1.0.0.2 -> 2.0.0.2
    tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
    fragment id 0x0000
  ICMP echo_request checksum 0x7a6e id 1
00:05:44:786523: ip4-glean
    ICMP: 1.0.0.2 -> 2.0.0.2
      tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
      fragment id 0x0000
    ICMP echo_request checksum 0x7a6e id 1
00:05:44:786547: ip4-drop
    ICMP: 1.0.0.2 -> 2.0.0.2
      tos 0x00, ttl 64, length 64, checksum 0x77ba dscp CS0 ecn NON_ECN
      fragment id 0x0000
    ICMP echo_request checksum 0x7a6e id 1
00:05:44:786568: error-drop
  rx:pg0
00:05:44:786591: drop
  ip4-glean: ARP requests sent

Use a PCAP file with PG

The packet generator can also replay a pcap file directly, for example:

 DBGvpp# create packet-generator interface pg0
 DBGvpp# packet-generator new pcap /tmp/mypcap.pcap source pg0 name s
 DBGvpp# packet-generator enable-stream

VPP Wiki

Home

Clone this wiki locally