NAT44 performance testing with TRex

Setup:

        TRex host                             VPP host
----------------------------      ---------------------------------------------
|                          |      |                                           |
| 04:00.0/172.16.1.2/port 0|<---->|04:00.1/172.16.1.1/TenGigabitEthernet4/0/1 |
|                          |      |                                           |
| 04:00.1/172.16.2.2/port 1|<---->|04:00.0/172.16.2.1/TenGigabitEthernet4/0/0 |
|                          |      |                                           |
----------------------------      ---------------------------------------------

How to use TRex:
1) Copy configuration file to /etc/trex_cfg.yaml or use --cfg option in next step
2) Start TRex as a server 'sudo ./t-rex-64 -i'
3) Connect with console './trex-console'
4) Resolve destination addresses 'reset ; service ; arp ; service --off'
5) Start traffic to open sessions in2out 'start -f stl/nat_10ks.py -m 10mbps -p 1' or out2in 'start -f stl/nat_out2in_10ks.py -m 10mbps -p 0'
6) After all sessions are opened update stream rate to 100% 'update -a -m 100%'
7) Show dynamic statistic 'tui'
8) Exit dynamic statistic 'q'
9) Stop traffic 'stop -a'
10) Sessions per second (slowpath) test 'reset ; service ; arp ; service --off; start -f stl/nat_ses_open.py -m 100% -p 1 -d 1' and 'show nat44' in VPP CLI to see number of opened sessions

VPP config files:
in2out testing nat_dynamic
for out2in testing generate config using 'nat_static_gen_cfg.py N'

References:
https://github.com/cisco-system-traffic-generator/trex-core/blob/master/doc/trex_stateless.asciidoc
https://github.com/cisco-system-traffic-generator/trex-core/blob/master/doc/trex_console.asciidoc
https://wiki.fd.io/view/VPP/NAT#NAT44
