Debugging

the anatomy of a route:

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.

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-balancing, 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:

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:

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:

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:

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:

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 adjacency that was contributed by path 26.