VNET (VPP Network Stack)

The files associated with the VPP network stack layer are located in the ./src/vnet folder. The Network Stack Layer is basically an instantiation of the code in the other layers. This layer has a vnet library that provides vectorized layer-2 and 3 networking graph nodes, a packet generator, and a packet tracer.

In terms of building a packet processing application, vnet provides a platform-independent subgraph to which one connects a couple of device-driver nodes.

Typical RX connections include “ethernet-input” [full software classification, feeds ipv4-input, ipv6-input, arp-input etc.] and “ipv4-input-no-checksum” [if hardware can classify, perform ipv4 header checksum].

Effective graph dispatch function coding

Over the 15 years, multiple coding styles have emerged: a single/dual/quad loop coding model (with variations) and a fully-pipelined coding model.

Single/dual loops

The single/dual/quad loop model variations conveniently solve problems where the number of items to process is not known in advance: typical hardware RX-ring processing. This coding style is also very effective when a given node will not need to cover a complex set of dependent reads.

Here is an quad/single loop which can leverage up-to-avx512 SIMD vector units to convert buffer indices to buffer pointers:

static uword
simulated_ethernet_interface_tx (vlib_main_t * vm,
              vlib_node_runtime_t *
              node, vlib_frame_t * frame)
  u32 n_left_from, *from;
  u32 next_index = 0;
  u32 n_bytes;
  u32 thread_index = vm->thread_index;
  vnet_main_t *vnm = vnet_get_main ();
  vnet_interface_main_t *im = &vnm->interface_main;
  vlib_buffer_t *bufs[VLIB_FRAME_SIZE], **b;
  u16 nexts[VLIB_FRAME_SIZE], *next;

  n_left_from = frame->n_vectors;
  from = vlib_frame_vector_args (frame);

   * Convert up to VLIB_FRAME_SIZE indices in "from" to
   * buffer pointers in bufs[]
  vlib_get_buffers (vm, from, bufs, n_left_from);
  b = bufs;
  next = nexts;

   * While we have at least 4 vector elements (pkts) to process..
  while (n_left_from >= 4)
      /* Prefetch next quad-loop iteration. */
      if (PREDICT_TRUE (n_left_from >= 8))
      vlib_prefetch_buffer_header (b[4], STORE);
      vlib_prefetch_buffer_header (b[5], STORE);
      vlib_prefetch_buffer_header (b[6], STORE);
      vlib_prefetch_buffer_header (b[7], STORE);

       * $$$ Process 4x packets right here...
       * set next[0..3] to send the packets where they need to go

       do_something_to (b[0]);
       do_something_to (b[1]);
       do_something_to (b[2]);
       do_something_to (b[3]);

      /* Process the next 0..4 packets */
  b += 4;
  next += 4;
  n_left_from -= 4;
   * Clean up 0...3 remaining packets at the end of the incoming frame
  while (n_left_from > 0)
       * $$$ Process one packet right here...
       * set next[0..3] to send the packets where they need to go
       do_something_to (b[0]);

      /* Process the next packet */
      b += 1;
      next += 1;
      n_left_from -= 1;

   * Send the packets along their respective next-node graph arcs
   * Considerable locality of reference is expected, most if not all
   * packets in the inbound vector will traverse the same next-node
   * arc
  vlib_buffer_enqueue_to_next (vm, node, from, nexts, frame->n_vectors);

  return frame->n_vectors;

Given a packet processing task to implement, it pays to scout around looking for similar tasks, and think about using the same coding pattern. It is not uncommon to recode a given graph node dispatch function several times during performance optimization.

Creating Packets from Scratch

At times, it’s necessary to create packets from scratch and send them. Tasks like sending keepalives or actively opening connections come to mind. Its not difficult, but accurate buffer metadata setup is required.

Allocating Buffers

Use vlib_buffer_alloc, which allocates a set of buffer indices. For low-performance applications, it’s OK to allocate one buffer at a time. Note that vlib_buffer_alloc(…) does NOT initialize buffer metadata. See below.

In high-performance cases, allocate a vector of buffer indices, and hand them out from the end of the vector; decrement _vec_len(..) as buffer indices are allocated. See tcp_alloc_tx_buffers(…) and tcp_get_free_buffer_index(…) for an example.

Buffer Initialization Example

The following example shows the main points, but is not to be blindly cut-’n-pasted.

u32 bi0;
vlib_buffer_t *b0;
ip4_header_t *ip;
udp_header_t *udp;

/* Allocate a buffer */
if (vlib_buffer_alloc (vm, &bi0, 1) != 1)
  return -1;

b0 = vlib_get_buffer (vm, bi0);

/* At this point b0->current_data = 0, b0->current_length = 0 */

 * Copy data into the buffer. This example ASSUMES that data will fit
 * in a single buffer, and is e.g. an ip4 packet.
if (have_packet_rewrite)
     clib_memcpy (b0->data, data, vec_len (data));
     b0->current_length = vec_len (data);
     /* OR, build a udp-ip packet (for example) */
     ip = vlib_buffer_get_current (b0);
     udp = (udp_header_t *) (ip + 1);
     data_dst = (u8 *) (udp + 1);

     ip->ip_version_and_header_length = 0x45;
     ip->ttl = 254;
     ip->protocol = IP_PROTOCOL_UDP;
     ip->length = clib_host_to_net_u16 (sizeof (*ip) + sizeof (*udp) +
     ip->src_address.as_u32 = src_address->as_u32;
     ip->dst_address.as_u32 = dst_address->as_u32;
     udp->src_port = clib_host_to_net_u16 (src_port);
     udp->dst_port = clib_host_to_net_u16 (dst_port);
     udp->length = clib_host_to_net_u16 (vec_len (udp_data));
     clib_memcpy (data_dst, udp_data, vec_len(udp_data));

     if (compute_udp_checksum)
         /* RFC 7011 section 10.3.2. */
         udp->checksum = ip4_tcp_udp_compute_checksum (vm, b0, ip);
         if (udp->checksum == 0)
           udp->checksum = 0xffff;
    b0->current_length = vec_len (sizeof (*ip) + sizeof (*udp) +
                                 vec_len (udp_data));


/* sw_if_index 0 is the "local" interface, which always exists */
vnet_buffer (b0)->sw_if_index[VLIB_RX] = 0;

/* Use the default FIB index for tx lookup. Set non-zero to use another fib */
vnet_buffer (b0)->sw_if_index[VLIB_TX] = 0;

If your use-case calls for large packet transmission, use vlib_buffer_chain_append_data_with_alloc(…) to create the requisite buffer chain.

Enqueueing packets for lookup and transmission

The simplest way to send a set of packets is to use vlib_get_frame_to_node(…) to allocate fresh frame(s) to ip4_lookup_node or ip6_lookup_node, add the constructed buffer indices, and dispatch the frame using vlib_put_frame_to_node(…).

vlib_frame_t *f;
f = vlib_get_frame_to_node (vm, ip4_lookup_node.index);
f->n_vectors = vec_len(buffer_indices_to_send);
to_next = vlib_frame_vector_args (f);

for (i = 0; i < vec_len (buffer_indices_to_send); i++)
  to_next[i] = buffer_indices_to_send[i];

vlib_put_frame_to_node (vm, ip4_lookup_node_index, f);

It is inefficient to allocate and schedule single packet frames. That’s typical in case you need to send one packet per second, but should not occur in a for-loop!

Packet tracer

Vlib includes a frame element [packet] trace facility, with a simple debug CLI interface. The cli is straightforward: “trace add input-node-name count” to start capturing packet traces.

To trace 100 packets on a typical x86_64 system running the dpdk plugin: “trace add dpdk-input 100”. When using the packet generator: “trace add pg-input 100”

To display the packet trace: “show trace”

Each graph node has the opportunity to capture its own trace data. It is almost always a good idea to do so. The trace capture APIs are simple.

The packet capture APIs snapshoot binary data, to minimize processing at capture time. Each participating graph node initialization provides a vppinfra format-style user function to pretty-print data when required by the VLIB “show trace” command.

Set the VLIB node registration “.format_trace” member to the name of the per-graph node format function.

Here’s a simple example:

u8 * my_node_format_trace (u8 * s, va_list * args)
    vlib_main_t * vm = va_arg (*args, vlib_main_t *);
    vlib_node_t * node = va_arg (*args, vlib_node_t *);
    my_node_trace_t * t = va_arg (*args, my_trace_t *);

    s = format (s, "My trace data was: %d", t-><whatever>);

    return s;

The trace framework hands the per-node format function the data it captured as the packet whizzed by. The format function pretty-prints the data as desired.

Graph Dispatcher Pcap Tracing

The vpp graph dispatcher knows how to capture vectors of packets in pcap format as they’re dispatched. The pcap captures are as follows:

VPP graph dispatch trace record description:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   | Major Version | Minor Version | NStrings      | ProtoHint     |
   | Buffer index (big endian)                                     |
   + VPP graph node name ...     ...               | NULL octet    |
   | Buffer Metadata ... ...                       | NULL octet    |
   | Buffer Opaque ... ...                         | NULL octet    |
   | Buffer Opaque 2 ... ...                       | NULL octet    |
   | VPP ASCII packet trace (if NStrings > 4)      | NULL octet    |
   | Packet data (up to 16K)                                       |

Graph dispatch records comprise a version stamp, an indication of how many NULL-terminated strings will follow the record header and preceed packet data, and a protocol hint.

The buffer index is an opaque 32-bit cookie which allows consumers of these data to easily filter/track single packets as they traverse the forwarding graph.

Multiple records per packet are normal, and to be expected. Packets will appear multiple times as they traverse the vpp forwarding graph. In this way, vpp graph dispatch traces are significantly different from regular network packet captures from an end-station. This property complicates stateful packet analysis.

Restricting stateful analysis to records from a single vpp graph node such as “ethernet-input” seems likely to improve the situation.

As of this writing: major version = 1, minor version = 0. Nstrings SHOULD be 4 or 5. Consumers SHOULD be wary values less than 4 or greater than 5. They MAY attempt to display the claimed number of strings, or they MAY treat the condition as an error.

Here is the current set of protocol hints:

typedef enum
  } vlib_node_proto_hint_t;

Example: VLIB_NODE_PROTO_HINT_IP6 means that the first octet of packet data SHOULD be 0x60, and should begin an ipv6 packet header.

Downstream consumers of these data SHOULD pay attention to the protocol hint. They MUST tolerate inaccurate hints, which MAY occur from time to time.

Dispatch Pcap Trace Debug CLI

To start a dispatch trace capture of up to 10,000 trace records:

pcap dispatch trace on max 10000 file dispatch.pcap

To start a dispatch trace which will also include standard vpp packet tracing for packets which originate in dpdk-input:

pcap dispatch trace on max 10000 file dispatch.pcap buffer-trace dpdk-input 1000

To save the pcap trace, e.g. in /tmp/dispatch.pcap:

pcap dispatch trace off

Wireshark dissection of dispatch pcap traces

It almost goes without saying that we built a companion wireshark dissector to display these traces. As of this writing, we have upstreamed the wireshark dissector.

Since it will be a while before wireshark/master/latest makes it into all of the popular Linux distros, please see the “How to build a vpp dispatch trace aware Wireshark” page for build info.

Here is a sample packet dissection, with some fields omitted for clarity. The point is that the wireshark dissector accurately displays all of the vpp buffer metadata, and the name of the graph node in question.

Frame 1: 2216 bytes on wire (17728 bits), 2216 bytes captured (17728 bits)
    Encapsulation type: USER 13 (58)
    [Protocols in frame: vpp:vpp-metadata:vpp-opaque:vpp-opaque2:eth:ethertype:ip:tcp:data]
VPP Dispatch Trace
    BufferIndex: 0x00036663
NodeName: ethernet-input
VPP Buffer Metadata
    Metadata: flags:
    Metadata: current_data: 0, current_length: 102
    Metadata: current_config_index: 0, flow_id: 0, next_buffer: 0
    Metadata: error: 0, n_add_refs: 0, buffer_pool_index: 0
    Metadata: trace_index: 0, recycle_count: 0, len_not_first_buf: 0
    Metadata: free_list_index: 0
VPP Buffer Opaque
    Opaque: raw: 00000007 ffffffff 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    Opaque: sw_if_index[VLIB_RX]: 7, sw_if_index[VLIB_TX]: -1
    Opaque: L2 offset 0, L3 offset 0, L4 offset 0, feature arc index 0
    Opaque: ip.adj_index[VLIB_RX]: 0, ip.adj_index[VLIB_TX]: 0
    Opaque: ip.flow_hash: 0x0, ip.save_protocol: 0x0, ip.fib_index: 0
    Opaque: ip.save_rewrite_length: 0, ip.rpf_id: 0
    Opaque: ip.icmp.type: 0 ip.icmp.code: 0, 0x0
    Opaque: ip.reass.next_index: 0, ip.reass.estimated_mtu: 0
    Opaque: ip.reass.fragment_first: 0 ip.reass.fragment_last: 0
    Opaque: ip.reass.range_first: 0 ip.reass.range_last: 0
    Opaque: ip.reass.next_range_bi: 0x0, ip.reass.ip6_frag_hdr_offset: 0
    Opaque: mpls.ttl: 0, mpls.exp: 0, mpls.first: 0, mpls.save_rewrite_length: 0, mpls.bier.n_bytes: 0
    Opaque: l2.feature_bitmap: 00000000, l2.bd_index: 0, l2.l2_len: 0, l2.shg: 0, l2.l2fib_sn: 0, l2.bd_age: 0
    Opaque: l2.feature_bitmap_input:   none configured, L2.feature_bitmap_output:   none configured
    Opaque: l2t.next_index: 0, l2t.session_index: 0
    Opaque: l2_classify.table_index: 0, l2_classify.opaque_index: 0, l2_classify.hash: 0x0
    Opaque: policer.index: 0
    Opaque: ipsec.flags: 0x0, ipsec.sad_index: 0
    Opaque: map.mtu: 0
    Opaque: map_t.v6.saddr: 0x0, map_t.v6.daddr: 0x0, map_t.v6.frag_offset: 0, map_t.v6.l4_offset: 0
    Opaque: map_t.v6.l4_protocol: 0, map_t.checksum_offset: 0, map_t.mtu: 0
    Opaque: ip_frag.mtu: 0, ip_frag.next_index: 0, ip_frag.flags: 0x0
    Opaque: cop.current_config_index: 0
    Opaque: lisp.overlay_afi: 0
    Opaque: tcp.connection_index: 0, tcp.seq_number: 0, tcp.seq_end: 0, tcp.ack_number: 0, tcp.hdr_offset: 0, tcp.data_offset: 0
    Opaque: tcp.data_len: 0, tcp.flags: 0x0
    Opaque: sctp.connection_index: 0, sctp.sid: 0, sctp.ssn: 0, sctp.tsn: 0, sctp.hdr_offset: 0
    Opaque: sctp.data_offset: 0, sctp.data_len: 0, sctp.subconn_idx: 0, sctp.flags: 0x0
    Opaque: snat.flags: 0x0
VPP Buffer Opaque2
    Opaque2: raw: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
    Opaque2: qos.bits: 0, qos.source: 0
    Opaque2: loop_counter: 0
    Opaque2: gbp.flags: 0, gbp.src_epg: 0
    Opaque2: pg_replay_timestamp: 0
Ethernet II, Src: 06:d6:01:41:3b:92 (06:d6:01:41:3b:92), Dst: IntelCor_3d:f6    Transmission Control Protocol, Src Port: 22432, Dst Port: 54084, Seq: 1, Ack: 1, Len: 36
    Source Port: 22432
    Destination Port: 54084
    TCP payload (36 bytes)
Data (36 bytes)

0000  cf aa 8b f5 53 14 d4 c7 29 75 3e 56 63 93 9d 11   ....S...)u>Vc...
0010  e5 f2 92 27 86 56 4c 21 ce c5 23 46 d7 eb ec 0d   ...'.VL!..#F....
0020  a8 98 36 5a                                       ..6Z
    Data: cfaa8bf55314d4c729753e5663939d11e5f2922786564c21…
    [Length: 36]

It’s a matter of a couple of mouse-clicks in Wireshark to filter the trace to a specific buffer index. With that specific kind of filtration, one can watch a packet walk through the forwarding graph; noting any/all metadata changes, header checksum changes, and so forth.

This should be of significant value when developing new vpp graph nodes. If new code mispositions b->current_data, it will be completely obvious from looking at the dispatch trace in wireshark.

pcap rx, tx, and drop tracing

vpp also supports rx, tx, and drop packet capture in pcap format, through the “pcap trace” debug CLI command.

This command is used to start or stop a packet capture, or show the status of packet capture. Each of “pcap trace rx”, “pcap trace tx”, and “pcap trace drop” is implemented. Supply one or more of “rx”, “tx”, and “drop” to enable multiple simultaneous capture types.

These commands have the following optional parameters:

  • rx - trace received packets.

  • tx - trace transmitted packets.

  • drop - trace dropped packets.

  • max nnnn - file size, number of packet captures. Once packets have been received, the trace buffer buffer is flushed to the indicated file. Defaults to 1000. Can only be updated if packet capture is off.

  • max-bytes-per-pkt nnnn - maximum number of bytes to trace on a per-packet basis. Must be >32 and less than 9000. Default value:

  • filter - Use the pcap trace rx / tx / drop filter, which must be configured. Use classify filter pcap… to configure the filter. The filter will only be executed if the per-interface or any-interface tests fail.

  • intfc interface | any - Used to specify a given interface, or use ‘any’ to run packet capture on all interfaces. ‘any’ is the default if not provided. Settings from a previous packet capture are preserved, so ‘any’ can be used to reset the interface setting.

  • file filename - Used to specify the output filename. The file will be placed in the ‘/tmp’ directory. If filename already exists, file will be overwritten. If no filename is provided, ‘/tmp/rx.pcap or tx.pcap’ will be used, depending on capture direction. Can only be updated when pcap capture is off.

  • status - Displays the current status and configured attributes associated with a packet capture. If packet capture is in progress, ‘status’ also will return the number of packets currently in the buffer. Any additional attributes entered on command line with a ‘status’ request will be ignored.

  • filter - Capture packets which match the current packet trace filter set. See next section. Configure the capture filter first.

packet trace capture filtering

The “classify filter pcap | | trace” debug CLI command constructs an arbitrary set of packet classifier tables for use with “pcap trace rx | tx | drop,” and with the vpp packet tracer on a per-interface or system-wide basis.

Packets which match a rule in the classifier table chain will be traced. The tables are automatically ordered so that matches in the most specific table are tried first.

It’s reasonably likely that folks will configure a single table with one or two matches. As a result, we configure 8 hash buckets and 128K of match rule space by default. One can override the defaults by specifying “buckets ” and “memory-size ” as desired.

To build up complex filter chains, repeatedly issue the classify filter debug CLI command. Each command must specify the desired mask and match values. If a classifier table with a suitable mask already exists, the CLI command adds a match rule to the existing table. If not, the CLI command add a new table and the indicated mask rule

Configure a simple pcap classify filter

classify filter pcap mask l3 ip4 src match l3 ip4 src
pcap trace rx max 100 filter

Configure a simple per-interface capture filter

classify filter GigabitEthernet3/0/0 mask l3 ip4 src match l3 ip4 src"
pcap trace rx max 100 intfc GigabitEthernet3/0/0

Note that per-interface capture filters are always applied.

Clear per-interface capture filters

classify filter GigabitEthernet3/0/0 del

Configure another fairly simple pcap classify filter

classify filter pcap mask l3 ip4 src dst match l3 ip4 src dst
pcap trace tx max 100 filter

Configure a vpp packet tracer filter

classify filter trace mask l3 ip4 src dst match l3 ip4 src dst
trace add dpdk-input 100 filter

Clear all current classifier filters

classify filter [pcap | <interface> | trace] del

To inspect the classifier tables

show classify table [verbose]

The verbose form displays all of the match rules, with hit-counters.

Terse description of the “mask ” syntax:

l2 src dst proto tag1 tag2 ignore-tag1 ignore-tag2 cos1 cos2 dot1q dot1ad
l3 ip4 <ip4-mask> ip6 <ip6-mask>
<ip4-mask> version hdr_length src[/width] dst[/width]
           tos length fragment_id ttl protocol checksum
<ip6-mask> version traffic-class flow-label src dst proto
           payload_length hop_limit protocol
l4 tcp <tcp-mask> udp <udp_mask> src_port dst_port
<tcp-mask> src dst  # ports
<udp-mask> src_port dst_port

To construct matches, add the values to match after the indicated keywords in the mask syntax. For example: “… mask l3 ip4 src” -> “… match l3 ip4 src”

VPP Packet Generator

We use the VPP packet generator to inject packets into the forwarding graph. The packet generator can replay pcap traces, and generate packets out of whole cloth at respectably high performance.

The VPP pg enables quite a variety of use-cases, ranging from functional testing of new data-plane nodes to regression testing to performance tuning.

PG setup scripts

PG setup scripts describe traffic in detail, and leverage vpp debug CLI mechanisms. It’s reasonably unusual to construct a pg setup script which doesn’t include a certain amount of interface and FIB configuration.

For example:

loop create
set int ip address loop0
set int state loop0 up

packet-generator new {
    name pg0
    limit 100
    rate 1e6
    size 300-300
    interface loop0
    node ethernet-input
    data { IP4: 1.2.3 -> 4.5.6
           UDP: - ->
           UDP: 1234 -> 2345
           incrementing 286

A packet generator stream definition includes two major sections: - Stream Parameter Setup - Packet Data

Stream Parameter Setup

Given the example above, let’s look at how to set up stream parameters:

  • name pg0 - Name of the stream, in this case “pg0”

  • limit 1000 - Number of packets to send when the stream is enabled. “limit 0” means send packets continuously.

  • maxframe <nnn> - Maximum frame size. Handy for injecting multiple frames no larger than <nnn>. Useful for checking dual / quad loop codes

  • rate 1e6 - Packet injection rate, in this case 1 MPPS. When not specified, the packet generator injects packets as fast as possible

  • size 300-300 - Packet size range, in this case send 300-byte packets

  • interface loop0 - Packets appear as if they were received on the specified interface. This datum is used in multiple ways: to select graph arc feature configuration, to select IP FIBs. Configure features e.g. on loop0 to exercise those features.

  • tx-interface <name> - Packets will be transmitted on the indicated interface. Typically required only when injecting packets into post-IP-rewrite graph nodes.

  • pcap <filename> - Replay packets from the indicated pcap capture file. “make test” makes extensive use of this feature: generate packets using scapy, save them in a .pcap file, then inject them into the vpp graph via a vpp pg “pcap <filename>” stream definition

  • worker <nn> - Generate packets for the stream using the indicated vpp worker thread. The vpp pg generates and injects O(10 MPPS / core). Use multiple stream definitions and worker threads to generate and inject enough traffic to easily fill a 40 gbit pipe with small packets.

Data definition

Packet generator data definitions make use of a layered implementation strategy. Networking layers are specified in order, and the notation can seem a bit counter-intuitive. In the example above, the data definition stanza constructs a set of L2-L4 headers layers, and uses an incrementing fill pattern to round out the requested 300-byte packets.

  • IP4: 1.2.3 -> 4.5.6 - Construct an L2 (MAC) header with the ip4 ethertype (0x800), src MAC address of 00:01:00:02:00:03 and dst MAC address of 00:04:00:05:00:06. Mac addresses may be specified in either xxxx.xxxx.xxxx format or xx:xx:xx:xx:xx:xx format.

  • UDP: - -> - Construct an incrementing set of L3 (IPv4) headers for successive packets with source addresses ranging from .10 to .254. All packets in the stream have a constant dest address of Set the protocol field to 17, UDP.

  • UDP: 1234 -> 2345 - Set the UDP source and destination ports to 1234 and 2345, respectively

  • incrementing 256 - Insert up to 256 incrementing data bytes.

Obvious variations involve “s/IP4/IP6/” in the above, along with changing from IPv4 to IPv6 address notation.

The vpp pg can set any / all IPv4 header fields, including tos, packet length, mf / df / fragment id and offset, ttl, protocol, checksum, and src/dst addresses. Take a look at ../src/vnet/ip/ip[46]_pg.c for details.

If all else fails, specify the entire packet data in hex:

  • hex 0xabcd… - copy hex data verbatim into the packet

When replaying pcap files (“pcap <filename>”), do not specify a data stanza.

Diagnosing “packet-generator new” parse failures

If you want to inject packets into a brand-new graph node, remember to tell the packet generator debug CLI how to parse the packet data stanza.

If the node expects L2 Ethernet MAC headers, specify “.unformat_buffer = unformat_ethernet_header”:

VLIB_REGISTER_NODE (ethernet_input_node) =
  .unformat_buffer = unformat_ethernet_header,

Beyond that, it may be necessary to set breakpoints in …/src/vnet/pg/cli.c. Debug image suggested.

When debugging new nodes, it may be far simpler to directly inject ethernet frames - and add a corresponding vlib_buffer_advance in the new node - than to modify the packet generator.

Debug CLI

The descriptions above describe the “packet-generator new” debug CLI in detail.

Additional debug CLI commands include:

vpp# packet-generator enable [<stream-name>]

which enables the named stream, or all streams.

vpp# packet-generator disable [<stream-name>]

disables the named stream, or all streams.

vpp# packet-generator delete <stream-name>

Deletes the named stream.

vpp# packet-generator configure <stream-name> [limit <nnn>]
     [rate <f64-pps>] [size <nn>-<nn>]

Changes stream parameters without having to recreate the entire stream definition. Note that re-issuing a “packet-generator new” command will correctly recreate the named stream.