SDN Static Routing using Ryu Controller + Mininet

Course: UE24CS252B – Computer Networks, PES University
Project: SDN Mininet-based Simulation – Static Routing using SDN Controller
Controller: Ryu (OpenFlow 1.3)
Emulator: Mininet

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Problem Statement

Implement static routing paths in a Software-Defined Network using a Ryu controller that proactively installs flow rules into OpenFlow switches the moment they connect. Unlike dynamic/reactive controllers, all routes are explicitly defined by the controller — demonstrating full SDN control plane authority over the data plane.

The controller also runs a background monitor thread that reinstalls rules every 10 seconds, ensuring routing paths remain unchanged (regression-safe).

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Topology

h1 (10.0.0.1) --+
                 s1 -------- s2 -------- s3 --+-- h3 (10.0.0.3)
h2 (10.0.0.2) --+                             +-- h4 (10.0.0.4)

Node	IP Address	MAC Address	Connected To
h1	10.0.0.1/24	00:00:00:00:00:01	s1 port 1
h2	10.0.0.2/24	00:00:00:00:00:02	s1 port 2
h3	10.0.0.3/24	00:00:00:00:00:03	s3 port 1
h4	10.0.0.4/24	00:00:00:00:00:04	s3 port 2
s1	dpid=1	—	h1, h2, s2
s2	dpid=2	—	s1, s3
s3	dpid=3	—	h3, h4, s2

Port Mapping

Switch	Port 1	Port 2	Port 3
s1	h1	h2	s2
s2	s1	s3	—
s3	h3	h4	s2

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File Structure

SDN-Static-Routing/
├── static_routing.py      # Ryu controller – installs static flow rules
├── topology.py            # Mininet topology – 3 switches, 4 hosts
├── regression_test.py     # Regression test – verifies rules persist
└── README.md

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Design & Implementation

Controller Logic (static_routing.py)

• Proactive flow installation: On EventOFPSwitchFeatures (switch connect), the controller immediately pushes all flow rules — no waiting for packets.
• Match-Action rules: Each rule matches on eth_type=0x0800 (IPv4) + ipv4_dst and outputs to the correct port.
• ARP handling: ARP packets are flooded (OFPP_FLOOD) so hosts can resolve MACs.
• Regression monitor: A background hub.spawn thread reinstalls rules every 10 seconds — ensuring static routes persist even if rules are deleted.
• OpenFlow 1.3: Uses OFPFlowMod with priority, match, and action fields.

Static Routing Table

Switch s1 (dpid=1)

Priority	Match	Action
20	IPv4 dst=10.0.0.1	output port 1 (h1)
20	IPv4 dst=10.0.0.2	output port 2 (h2)
10	IPv4 (any)	output port 3 (→ s2)
5	ARP	FLOOD

Switch s2 (dpid=2)

Priority	Match	Action
20	IPv4 dst=10.0.0.1	output port 1 (→ s1)
20	IPv4 dst=10.0.0.2	output port 1 (→ s1)
20	IPv4 dst=10.0.0.3	output port 2 (→ s3)
20	IPv4 dst=10.0.0.4	output port 2 (→ s3)
5	ARP	FLOOD

Switch s3 (dpid=3)

Priority	Match	Action
20	IPv4 dst=10.0.0.3	output port 1 (h3)
20	IPv4 dst=10.0.0.4	output port 2 (h4)
10	IPv4 (any)	output port 3 (→ s2)
5	ARP	FLOOD

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Setup & Installation

Prerequisites

# Mininet
sudo apt install mininet -y

# Open vSwitch
sudo apt install openvswitch-switch -y

# Python 3.10 virtual environment (required — Ryu does not support Python 3.12)
sudo apt install python3.10 python3.10-venv -y
python3.10 -m venv ~/ryu-env
source ~/ryu-env/bin/activate

# Install Ryu with compatible dependencies
pip install pip==21.3.1 setuptools==59.6.0
pip install eventlet==0.30.2 dnspython==1.16.0 six==1.16.0
pip install ryu==4.34

Apply compatibility patches (one time only)

cat > ~/fix_eventlet.sh << 'EOF'
#!/bin/bash
SITE=~/ryu-env/lib/python3.10/site-packages
sed -i 's/base.is_timeout = property(lambda _: True)/pass  # patched/' $SITE/eventlet/timeout.py
sed -i 's/six.get_function_code(_original_pyio.open),/_original_pyio.open.__func__.__code__,/' $SITE/eventlet/greenio/py3.py
sed -i 's/from eventlet.wsgi import ALREADY_HANDLED/ALREADY_HANDLED = object()/' $SITE/ryu/app/wsgi.py
sed -i 's/collections.MutableMapping/collections.abc.MutableMapping/' $SITE/dns/namedict.py
echo "All patches applied!"
EOF
bash ~/fix_eventlet.sh

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Execution Steps

Step 1 — Start Ryu Controller (Terminal 1)

cd ~/sdn-static-routing
source ~/ryu-env/bin/activate
ryu-manager static_routing.py --observe-links

Wait until you see:

Static Routing Controller started

Step 2 — Start Mininet Topology (Terminal 2)

cd ~/Downloads/SDN-Static-Routing-main
sudo python3 topology.py

⚠️ Never run sudo mn -c while Ryu is running — it terminates ryu-manager.

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Test Scenarios & Expected Output

Scenario 1 — Full Connectivity (pingall)

mininet> pingall

Expected:

h1 -> h2 h3 h4
h2 -> h1 h3 h4
h3 -> h1 h2 h4
h4 -> h1 h2 h3
*** Results: 0% dropped (12/12 received)

Scenario 2 — Specific Path: h1 → h4

mininet> h1 ping -c 4 h4

Expected:

64 bytes from 10.0.0.4: icmp_seq=1 ttl=64 time=0.632 ms
64 bytes from 10.0.0.4: icmp_seq=2 ttl=64 time=0.118 ms
64 bytes from 10.0.0.4: icmp_seq=3 ttl=64 time=0.106 ms
64 bytes from 10.0.0.4: icmp_seq=4 ttl=64 time=0.089 ms
4 packets transmitted, 4 received, 0% packet loss
rtt min/avg/max/mdev = 0.089/0.236/0.632/0.228 ms

Path taken: h1 → s1 (port3) → s2 (port2) → s3 (port2) → h4

Scenario 3 — Flow Table Verification

mininet> sh ovs-ofctl dump-flows s1 -O OpenFlow13
mininet> sh ovs-ofctl dump-flows s2 -O OpenFlow13
mininet> sh ovs-ofctl dump-flows s3 -O OpenFlow13

Expected (s1):

priority=20,ip,nw_dst=10.0.0.1 actions=output:"s1-eth1"
priority=20,ip,nw_dst=10.0.0.2 actions=output:"s1-eth2"
priority=10,ip actions=output:"s1-eth3"
priority=5,arp actions=FLOOD

Scenario 4 — Throughput Measurement (iperf)

mininet> h4 iperf -s &
mininet> h1 iperf -c 10.0.0.4 -t 5

Scenario 5 — Regression Test

Open Terminal 3 while Mininet is still running:

sudo python3 regression_test.py

Expected:

=== BEFORE: Capturing flow rules ===
s1: 4 rules
s2: 5 rules
s3: 4 rules

=== Deleting all flow rules ===
Deleted rules on s1, s2, s3

Waiting 5s for controller to reinstall rules...

=== AFTER: Capturing flow rules ===
s1: 4 rules
s2: 5 rules
s3: 4 rules

=== Regression Result ===
s1: before=4 rules, after=4 rules → PASS
s2: before=5 rules, after=5 rules → PASS
s3: before=4 rules, after=4 rules → PASS

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Cleanup

mininet> exit
sudo mn -c

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References

1. Ryu SDN Framework Documentation — https://ryu.readthedocs.io/en/latest/
2. Mininet Walkthrough — https://mininet.org/walkthrough/
3. OpenFlow 1.3 Specification — https://opennetworking.org/wp-content/uploads/2014/10/openflow-spec-v1.3.0.pdf
4. Mininet Overview — https://mininet.org/overview/
5. Ryu GitHub — https://github.com/faucetsdn/ryu
6. PES University Course Material — UE24CS252B Computer Networks