+--+
+------------+s2+------------+
| +--+ |
| |
| |
| +--+ |
| +---+s3+----+ |
+--+--+ | +--+ | +--+--+
+--+ | +-----+ +----+ | +--+
|h1+------+ s1 | | s6 +-----+h2|
+--+ | +-----+ +----+ | +--+
+--+--+ | +--+ | +--+--+
| +---+s4+----+ |
| +--+ |
| |
| |
| +--+ |
+------------+s5+------------+
+--+
In this example we implement a layer 3 forwarding switch that is able to load balance traffic
towards a destination across equal cost paths. To load balance traffic across multiple ports we will implement ECMP (Equal-Cost
Multi-Path) routing. When a packet with multiple candidate paths arrives, our switch should assign the next-hop by hashing some fields from the
header and compute this hash value modulo the number of possible equal paths. For example in the topology above, when s1 has to send
a packet to h2, the switch should determine the output port by computing: hash(some-header-fields) mod 4. To prevent out of order packets, ECMP hashing is done on a per-flow basis,
which means that all packets with the same source and destination IP addresses and the same source and destination
ports always hash to the same next hop.
Run the topology:
sudo p4run
Monitor all the interfaces connecting s1 to the 4 middle switches. You can use tshark, tcpdump:
sudo tshark -i s1-eth2
(Do the same with the other three interfaces).
Send packets with random ports from h1:
mx h1
python send.py 10.0.6.2 1000