docs: vpp stateless traffic generator

Add a use-case writeup.

Type: docs

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: Ib6e79e80455edbdeedcc96943dd98f16c57c559e

Author: Dave Barach

docs/usecases/index.rst

@@ -20,3 +20,4 @@ extensive list, but should give a sampling of the many features contained in FD.
    networksim
    webapp
    container_test
+   trafficgen

docs/usecases/trafficgen.md

@@ -0,0 +1,105 @@
+Vpp Stateless Traffic Generation
+================================
+
+It's simple to configure vpp as a high-performance stateless traffic
+generator. A couple of vpp worker threads running on an older system
+can easily generate 20 MPPS' worth of traffic.
+
+In the configurations shown below, we connect a vpp traffic generator
+and a vpp UUT using two 40 gigabit ethernet ports on each system:
+
+```
+ +-------------------+           +-------------------+
+ | traffic generator |           | UUT               |
+ | port 0            | <=======> | port 0            |
+ | 192.168.40.2/24   |           | 192.168.40.1/24   |
+ +-------------------+           +-------------------+
+
+ +-------------------+           +-------------------+
+ | traffic generator |           | UUT               |
+ | port 1            | <=======> | port 1            |
+ | 192.168.41.2/24   |           | 192.168.41.1/24   |
+ +-------------------+           +-------------------+
+```
+
+Traffic Generator Setup Script
+------------------------------
+
+```
+ set int ip address FortyGigabitEthernet2/0/0 192.168.40.2/24
+ set int ip address FortyGigabitEthernet2/0/1 192.168.41.2/24
+ set int state FortyGigabitEthernet2/0/0 up
+ set int state FortyGigabitEthernet2/0/1 up
+
+ comment { send traffic to the VPP UUT }
+
+ packet-generator new {
+     name worker0
+     worker 0
+     limit 0
+     rate 1.2e7
+     size 128-128
+     tx-interface FortyGigabitEthernet2/0/0
+     node FortyGigabitEthernet2/0/0-output
+     data { IP4: 1.2.40 -> 3cfd.fed0.b6c8
+            UDP: 192.168.40.10 -> 192.168.50.10
+            UDP: 1234 -> 2345
+            incrementing 114
+     }
+ }
+
+ packet-generator new {
+     name worker1
+     worker 1
+     limit 0
+     rate 1.2e7
+     size 128-128
+     tx-interface FortyGigabitEthernet2/0/1
+     node FortyGigabitEthernet2/0/1-output
+     data { IP4: 1.2.4 -> 3cfd.fed0.b6c9
+            UDP: 192.168.41.10 -> 192.168.51.10
+            UDP: 1234 -> 2345
+            incrementing 114
+     }
+ }
+
+ comment { delete return traffic on sight }
+
+ ip route add 192.168.50.0/24 via drop
+ ip route add 192.168.51.0/24 via drop
+```
+
+Note 1: the destination MAC addresses shown in the configuration (e.g.
+3cfd.fed0.b6c8 and 3cfd.fed0.b6c9) **must** match the vpp UUT port MAC
+addresses.
+
+Note 2: this script assumes that /etc/vpp/startup.conf and/or the
+command-line in use specifies (at least) two worker threads. Uncomment
+"workers 2" in the cpu configuration section of /etc/vpp/startup.conf:
+
+```
+ ## Specify a number of workers to be created
+ ## Workers are pinned to N consecutive CPU cores while skipping "skip-cores" CPU core(s)
+ ## and main thread's CPU core
+ workers 2
+```
+
+Any plausible packet generator script - including one which replays
+pcap captures - can be used.
+
+
+UUT Setup Script
+----------------
+
+The vpp UUT uses a couple of static routes to forward traffic back to
+the traffic generator:
+
+```
+ set int ip address FortyGigabitEthernet2/0/0 192.168.40.1/24
+ set int ip address FortyGigabitEthernet2/0/1 192.168.41.1/24
+ set int state FortyGigabitEthernet2/0/0 up
+ set int state FortyGigabitEthernet2/0/1 up
+
+ ip route add 192.168.50.10/32 via 192.168.41.2
+ ip route add 192.168.51.10/32 via 192.168.40.2
+```