View source for VPP/How To Use The Packet Generator and Packet Tracer

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=== 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 <code>dpdk</code> 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 <tt>.../vpp/vnet/etc/scripts/arp4</tt> 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 <code>trace add</code> command arranges to trace 100 packets originating at the <code>pg-input</code> 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 <code>show trace</code> 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