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.
+
+```c
+ u32 bi0;
+ vlib_buffer_t *b0;
+ ip4_header_t *ip;
+ udp_header_t *udp;
+ vlib_buffer_free_list_t *fl;
+
+ /* Allocate a buffer */
+ if (vlib_buffer_alloc (vm, &bi0, 1) != 1)
+ return -1;
+
+ b0 = vlib_get_buffer (vm, bi0);
+
+ /* Initialize the buffer */
+ fl = vlib_buffer_get_free_list (vm, VLIB_BUFFER_DEFAULT_FREE_LIST_INDEX);
+ vlib_buffer_init_for_free_list (b0, fl);
+ VLIB_BUFFER_TRACE_TRAJECTORY_INIT (b0);
+
+ /* 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);
+ }
+ else
+ {
+ /* 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) +
+ vec_len(udp_data));
+ 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));
+
+ }
+ b0->flags |= (VLIB_BUFFER_TOTAL_LENGTH_VALID;
+
+ /* 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(...).
+
+```c
+ 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
-------------
set int state GigabitEthernet0/14/0 up
comment { dhcp server and host-stack access }
- tap connect lstack address 192.168.1.2/24
- set int l2 bridge tapcli-0 1
- set int state tapcli-0 up
+ create tap host-if-name lstack host-ip4-addr 192.168.1.2/24 host-ip4-gw 192.168.1.1
+ set int l2 bridge tap0 1
+ set int state tap0 up
comment { Configure NAT}
nat44 add interface address GigabitEthernet3/0/0
comment { bin dns_enable_disable }
comment { see patch below, which adds these commands }
service restart isc-dhcp-server
- add default linux route via 192.168.1.1
Patches
-------
-You'll need this patch to add the "service restart" and "add default
-linux route" commands::
+You'll need this patch to add the "service restart" command::
diff --git a/src/vpp/vnet/main.c b/src/vpp/vnet/main.c
index 6e136e19..69189c93 100644
+};
+/* *INDENT-ON* */
+
- +static clib_error_t *
- +add_default_linux_route_command_fn (vlib_main_t * vm,
- + unformat_input_t * input,
- + vlib_cli_command_t * c)
- +{
- + int rv __attribute__((unused));
- + ip4_address_t ip4_addr;
- + u8 *cmd;
- +
- + if (!unformat (input, "%U", unformat_ip4_address, &ip4_addr))
- + return clib_error_return (0, "default gateway address required...");
- +
- + cmd = format (0, "/sbin/route add -net 0.0.0.0/0 gw %U",
- + format_ip4_address, &ip4_addr);
- + vec_add1 (cmd, 0);
- +
- + rv = system (cmd);
- +
- + vlib_cli_output (vm, "%s", cmd);
- +
- + vec_free(cmd);
- +
- + return 0;
- +}
- +
- +/* *INDENT-OFF* */
- +VLIB_CLI_COMMAND (add_default_linux_route_command, static) = {
- + .path = "add default linux route via",
- + .short_help = "Adds default linux route: 0.0.0.0/0 via <addr>",
- + .function = add_default_linux_route_command_fn,
- +};
- +/* *INDENT-ON* */
- +
- +
+
Using the temporal mac filter plugin
------------------------------------
Code Review / vpp.git / commitdiff