docs/gettingstarted/developers/fib20/debugging.rst

.. _debugging:

Debugging
---------

the anatomy of a route:

.. code-block:: console

  BGvpp# sh ip fib 1.1.1.3/32
  ipv4-VRF:0, fib_index:0, flow hash:[src dst sport dport proto ] epoch:0 flags:none locks:[adjacency:1, recursive-resolution:4, default-route:1, ]
  1.1.1.0/24 fib:0 index:9 locks:2
    CLI refs:1 src-flags:added,contributing,active,
      path-list:[24] locks:4 flags:shared, uPRF-list:11 len:1 itfs:[1, ]
        path:[26] pl-index:24 ip4 weight=1 pref=0 attached-nexthop:  oper-flags:resolved,
          10.0.0.1 loop0
        [@0]: arp-ipv4: via 10.0.0.1 loop0

   forwarding:   unicast-ip4-chain
    [@0]: dpo-load-balance: [proto:ip4 index:11 buckets:1 uRPF:11 to:[0:0]]
      [0] [@3]: arp-ipv4: via 10.0.0.1 loop0

let's go line by line.

.. code-block:: console

     ipv4-VRF:0, fib_index:0, flow hash:[src dst sport dport proto ] epoch:0 flags:none locks:[adjacency:1, recursive-resolution:4, default-route:1, ]

Each field in turn:

- ipv4-VRF:0: the name of the table (as given by the user, or
  automatically generated by VPP).
- fib-index:0; in the VPP pool of FIB objects, this is index 0
- flow hash:[src dst sport dport proto ]: When calculating the flow
  hash to use for load-balanacing, these are the fields in the packet
  that are used. There is an API to change this per-table.
- epoch:0; Used during mark-n-sweep.
- flags:none; use the force, to find the per-table flags.
- locks: per-source reference counting, a table can only be deleted
  when all sources no longer reference it.

next line:

.. code-block:: console

   1.1.1.0/24 fib:0 index:9 locks:2

this shows the route that matched the show request. note that it is not
an exact match, it's an LPM. The route is in FIB index 0, its index
(in the VPP pool of fib_entry_t objects) is nine and there are two
references to the entry.
You'll get the same output if you type "sh fib entry 9"

next line:

.. code-block:: console

    CLI refs:1 src-flags:added,contributing,active,

the 'CLI' has sourced this route (it was added via CLI). This source
has been added (well duh) it is 'active', meaning it is the best
source, and it is contributing a forwarding object. There are some
scenarios where sources other than the active source contribute,
namely interpose sources.

next line:

.. code-block:: console

      path-list:[24] locks:4 flags:shared, uPRF-list:11 len:1 itfs:[1, ]

This is path-list inex 24 (see "sh fib path-list 24" this will also
show the  children), it is 'shared',
meaning that if other prefixes were to use the same set of paths,
then they would also use this path-list object. It has uRPF list 11 of
length 1 containing interface index 1 (which is loop0, see "sh int").

next line:

.. code-block:: console

        path:[26] pl-index:24 ip4 weight=1 pref=0 attached-nexthop:  oper-flags:resolved,
          10.0.0.1 loop0
        [@0]: arp-ipv4: via 10.0.0.1 loop0

This is path 26 (see "sh fib path 26"). It's a member of
path-list 24. It's ip4 has a weight of 1 and a preference of 0. It's
of type 'attached-nexthop' and currently resolved - woohoo.
It is a path 'via 10.0.0.1 loop0'. It is contributing an incomplete adjacency.
   
next line:

.. code-block:: console

  forwarding:   unicast-ip4-chain
    [@0]: dpo-load-balance: [proto:ip4 index:11 buckets:1 uRPF:11 to:[0:0]]
      [0] [@3]: arp-ipv4: via 10.0.0.1 loop0

This section describes how packets of type 'unicast-ip4' will be
forwarded. It is the result of processing the path information from
above.
Here we see load-balance object 11, which has 1 bucket/choice. It is
also linked to uRPF instance 11 (which it got from path-list 24).
In bucket 0 there is the incomplete adjacnecy that was contributed by
path 26.