Generating traffic with VPP =========================== Vpp includes a fairly capable network simulator plugin, which can simulate real-world round-trip times and a configurable network packet loss rate. It’s perfect for evaluating the performance of a TCP stack under specified delay/bandwidth/loss conditions. The “nsim” plugin cross-connects two physical interfaces at layer 2, introducing the specified delay and network loss parameters. Reconfiguration on the fly is OK, with the proviso that packets held in the network simulator scheduling wheel will be lost. Configuration ------------- Configuration by debug CLI is simple. First, specify the simulator configuration: unidirectional delay (half of the desired RTT), the link bandwidth, and the expected average packet size. These parameters allow the network simulator allocate the right amount of buffering to produce the requested delay/bandwidth product. :: set nsim delay 25.0 ms bandwidth 10 gbit packet-size 128 To simulate network packet drops, add either “packets-per-drop ” or “drop-fraction [0.0 … 1.0]” parameters: :: set nsim delay 25.0 ms bandwidth 10 gbit packet-size 128 packets-per-drop 10000 Remember to configure the layer-2 cross-connect: :: nsim enable-disable <interface-1> <interface-2> Packet Generator Configuration ------------------------------ Here’s a unit-test configuration for the vpp packet generator: :: loop cre set int ip address loop0 11.22.33.1/24 set int state loop0 up loop cre set int ip address loop1 11.22.34.1/24 set int state loop1 up set nsim delay 1.0 ms bandwidth 10 gbit packet-size 128 packets-per-drop 1000 nsim enable-disable loop0 loop1 packet-generator new { name s0 limit 10000 size 128-128 interface loop0 node ethernet-input data { IP4: 1.2.3 -> 4.5.6 UDP: 11.22.33.44 -> 11.22.34.44 UDP: 1234 -> 2345 incrementing 114 } } For extra realism, the network simulator drops any specific packet with the specified probability. In this example, we see that slight variation from run to run occurs as it should. :: DBGvpp# pa en DBGvpp# sh err Count Node Reason 9991 nsim Packets buffered 9 nsim Network loss simulation drop packets 9991 ethernet-input l3 mac mismatch DBGvpp# clear err DBGvpp# pa en DBGvpp# sh err sh err Count Node Reason 9993 nsim Packets buffered 7 nsim Network loss simulation drop packets 9993 ethernet-input l3 mac mismatch