Tracepath
=========

Display VPP graph path information on current trace buffer entries
& filter trace output to only match a specific path.

Basic Usage
-----------

Start a trace, send traffic, then use ``show trace paths`` to see a summary of
all unique forwarding paths observed across all threads:

::

   vpp# trace add pg-input 100
   vpp# show trace paths

   Found 2 unique paths across all threads (showing top 2):

    [0] Count: 7  ID: 0x00000007c61bef93  Length:  7  Threads: [0]
        Path: pg-input -> ethernet-input -> ip4-input -> ip4-lookup -> ip4-drop -> error-drop -> drop

    [1] Count: 5  ID: 0x0000000707c1f778  Length:  7  Threads: [0]
        Path: pg-input -> ethernet-input -> ip4-input -> ip4-lookup -> ip4-rewrite -> pg1-output -> pg1-tx

Use ``show trace path <INDEX>`` to display the full packet traces for a given
path:

::

   vpp# show trace path 0

   ==================== Path [0] ====================
   Path: pg-input -> ethernet-input -> ip4-input -> ip4-lookup -> ip4-drop -> error-drop -> drop
   Threads: [0]  Count: 7

   --- Thread 0 vpp_main ---
   Packet 1

   00:00:00:682233: pg-input
     stream 0, 42 bytes, sw_if_index 1, next_node ethernet-input
   ....

Multiple path indices can be passed to ``show trace path``:

::

   vpp# show trace path 0 1

Usage with Trace Filters
------------------------

Trace filtering can be used in addition to tracepath commands to facilitate troubleshooting.

Using a classifier filter to trace only packets from a specific source IP:

::

   vpp# classify filter trace mask l3 ip4 src match l3 ip4 src 172.16.1.2
   vpp# clear trace
   vpp# trace add pg-input 1000 filter
   vpp# show trace paths

   Found 1 unique paths across all threads (showing top 1):

    [0] Count: 5  ID: 0xa2d74d57dc94f686  Length:  7  Threads: [0]
        Path: pg-input -> ethernet-input -> ip4-input -> ip4-lookup -> ip4-rewrite -> pg1-output -> pg1-tx

   vpp# show trace path 0

   ==================== Path [0] ====================

   Path: pg-input -> ethernet-input -> ip4-input -> ip4-lookup -> ip4-rewrite -> pg1-output -> pg1-tx
   Threads: [0]  Count: 5

   --- Thread 0 vpp_main ---
   Packet 1

   00:00:00:310785: pg-input
     stream 0, 42 bytes, sw_if_index 1, next_node ethernet-input
   ...
   00:00:00:310829: ip4-lookup
     fib 0 dpo-idx 5 flow hash: 0x00000000
     UDP: 172.16.1.2 -> 172.16.2.2
   ...
   00:00:00:310837: ip4-rewrite
     tx_sw_if_index 2 dpo-idx 5 : ipv4 via 172.16.2.2 pg1: mtu:9000 next:4
   ...

   vpp# classify filter trace del

Alternatively, use a BPF filter (from ``bpf_trace_filter`` plugin):

::

   vpp# set bpf trace filter {{src host 10.0.0.5}}
   vpp# set trace filter function bpf_trace_filter
   vpp# trace add pg-input 1000 filter
   vpp# show trace paths
   ...