infufrgs-2019-01

INF UFRGS 2019/1 Sample Code

Introduction

This directory contains sample code to help students of INF01002 Communication Protocols (2019/1) and CMP182 Computer Networks (2019/01) of the Institute of Informatics (INF) of the Federal University of Rio Grande do Sul (UFRGS) with learning the basics of P4 programming.

It consists of a simple IPv4 and Tunnel forwarding application. myprogram.p4 is used to program switches to do processing related to IPv4 forwarding and a simple tunneling technique. master-controller.py installs myprogram.p4 into switches and configures them with the necessary rules to do IPv4 forwarding and also to use a special tunnel for traffic between two hosts in the topology. stats-controller.py periodically reads some counters of the switches and shows this information to the user. topology.json defines the topology of the testbed network emulated for this sample directory. The topology of the emulated network is shown bellow and is composed of three switches (s1, s2, s3) configured in a triangle, each connected to one host (h1, h2, and h3). The hosts are assigned IPs of 10.0.1.1, 10.0.2.2, and 10.0.3.3.

Running the sample code

1. In your terminal application, open three shells.

2. In the first shell, run: make, This will:

   • compile myprogram.p4, and
   • start a Mininet instance with three switches (s1, s2, and s3) configured in a triangle, each connected to one host each connected to one host (h1, h2, and h3).
   • The hosts are assigned IPs of 10.0.1.1, 10.0.2.2, and 10.0.3.3.

3. You should now see a Mininet command prompt. Make h1 send ICMP messages to h2 with command h1 ping h2. Since at this moment no program and no forwarding rule have been installed into the switches, the ICMP packets will not reach h2.

4. To program the switches we will now launch the (master) controller. In the second opened shell, run: ./master-controller.py.

   The procedure of the master controller is divided into four phases. The first phase will simply install the myprogram.p4 code into switches. Since no forwarding rule has been configured into switches, ICMP packets will still not reach h2 in this Phase #1.

5. After having started the master controller, we may now run the stats controller. This controller periodically reads counter values from switches to help us see what are the switches doing tunneling. To launch the stats controller, in the third shell, run ./stats-controller.py. Initially it will print something similar to the following every other second.

   ----- Reading tunnel counters -----
   s1 MyIngress.ingressTunnelCounter 200:   0 packets --      0 bytes
   s3 MyIngress.forwardTunnelCounter 200:   0 packets --      0 bytes
   s2 MyIngress.egressTunnelCounter  200:   0 packets --      0 bytes
   
   s2 MyIngress.ingressTunnelCounter 100:   0 packets --      0 bytes
   s3 MyIngress.forwardTunnelCounter 100:   0 packets --      0 bytes
   s1 MyIngress.egressTunnelCounter  100:   0 packets --      0 bytes
   

6. Next, go back to the master controller shell and press ENTER. This controller will start the second phase. In this phase, the controller will populate the switches IPv4 forwarding tables with the necessary rules for every host in the topology to be able to send and receive packets from all of the other hosts.

   The ping session between hosts h1 and h2 should now start to work. Note that the TTL values reported by the ICMP messages is 62, which reflects the fact that there are two hops (s1 and s2) in the shortest path from h1 to h2. Note also, in the third shell, that all counters still have value 0, since no tunneling has yet been configured on the switches.

7. Go back to the second shell and press ENTER to start the third master controller phase. This phase modifies some of the rules on the IPv4 forwarding table and configures new rules on the Tunneling table. This results in the creation of the orange tunnel using the shortest path from h1 to h2 shown in the figure below.

   

   Traffic from h1 to h2 will now be forwarded using this tunnel. myprogram.p4 configures switches to decrease the TTL value of packets by 2 (instead of 1) when doing tunneling. Note that, now, the TTL values reported by the ICMP messages is 60, reflecting this TTL decreasing logic. The stats controller will also start showing values different from 0 since the ICMP packets are now being forwarded through the tunnel. More specifically, ingress and egress counters at s1 and s2 will have valeus greater than zero.

   The rules created and modified at each phase of the master controller are shown in this section of this README.

8. Finally, in the second shell press ENTER to start the fourth and final phase. In this phase, the master controller reconfigures the tunnel created in the previous phase to use the alternate path s1->s3->s2 (shown in the figure below) from h1 to h2. With this new configuration, the TTL reported by the ICMP messages will now be 58, indicating packets are being routed through the three-hop tunneled path (64 - 2x3 = 58). The forwarding counters in s3 will now start to be reported by the stats controller with values greater than 0.

   

This ends this step-by-step tutorial.

Table Rules by Phase

Phase 1

This phase only installs myprogram.p4 into switches, so only default program-defined drop() rules are created.

Switch S1

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
default	drop()	NEW

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
default	drop()	NEW

Switch S2

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
default	drop()	NEW

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
default	drop()	NEW

Switch S3

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
default	drop()	NEW

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
default	drop()	NEW

Phase 2

Switch S1

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	ipv4_forward(dstAddr="00:00:00:00:01:01", port=1)	NEW
10.0.2.2/32	ipv4_forward(dstAddr="00:00:00:02:02:00", port=2)	NEW
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:03:03:00", port=3)	NEW
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
default	drop()	UNCHANGED

Switch S2

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	ipv4_forward(dstAddr="00:00:00:01:01:00", port=2)	NEW
10.0.2.2/32	ipv4_forward(dstAddr="00:00:00:00:02:02", port=1)	NEW
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:03:03:00", port=3)	NEW
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
default	drop()	UNCHANGED

Switch S3

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	ipv4_forward(dstAddr="00:00:00:01:01:00", port=2)	NEW
10.0.2.2/32	ipv4_forward(dstAddr="00:00:00:02:02:00", port=3)	NEW
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:00:03:03", port=1)	NEW
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
default	drop()	UNCHANGED

Phase 3

Switch S1

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	ipv4_forward(dstAddr="00:00:00:00:01:01", port=1)	UNCHANGED
10.0.2.2/32	myTunnel_ingress(dst_id=200)	MODIFIED
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:03:03:00", port=3)	UNCHANGED
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
100	myTunnel_egress(dstAddr="00:00:00:00:01:01", port=1)	NEW
200	myTunnel_forward(port=2)	NEW
default	drop()	UNCHANGED

Switch S2

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	myTunnel_ingress(dst_id=100)	MODIFIED
10.0.2.2/32	ipv4_forward(dstAddr="00:00:00:00:02:02", port=1)	UNCHANGED
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:03:03:00", port=3)	UNCHANGED
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
100	myTunnel_forward(port=2)	NEW
200	myTunnel_egress(dstAddr="00:00:00:00:02:02", port=1)	NEW
default	drop()	UNCHANGED

Switch S3

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	ipv4_forward(dstAddr="00:00:00:01:01:00", port=2)	UNCHANGED
10.0.2.2/32	ipv4_forward(dstAddr="00:00:00:02:02:00", port=3)	UNCHANGED
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:00:03:03", port=1)	UNCHANGED
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
default	drop()	UNCHANGED

Phase 4

Switch S1

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	ipv4_forward(dstAddr="00:00:00:00:01:01", port=1)	UNCHANGED
10.0.2.2/32	myTunnel_ingress(dst_id=200)	UNCHANGED
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:03:03:00", port=3)	UNCHANGED
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
100	myTunnel_egress(dstAddr="00:00:00:00:01:01", port=1)	UNCHANGED
200	myTunnel_forward(port=3)	MODIFIED
default	drop()	UNCHANGED

Switch S2

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	myTunnel_ingress(dst_id=100)	UNCHANGED
10.0.2.2/32	ipv4_forward(dstAddr="00:00:00:00:02:02", port=1)	UNCHANGED
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:03:03:00", port=3)	UNCHANGED
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
100	myTunnel_forward(port=3)	MODIFIED
200	myTunnel_egress(dstAddr="00:00:00:00:02:02", port=1)	UNCHANGED
default	drop()	UNCHANGED

Switch S3

Table ipv4_lpm

Match (ipv4.dstAddr)	Action and Parameters	Status
10.0.1.1/32	ipv4_forward(dstAddr="00:00:00:01:01:00", port=2)	UNCHANGED
10.0.2.2/32	ipv4_forward(dstAddr="00:00:00:02:02:00", port=3)	UNCHANGED
10.0.3.3/32	ipv4_forward(dstAddr="00:00:00:00:03:03", port=1)	UNCHANGED
default	drop()	UNCHANGED

Table myTunnel_exact

Match (myTunnel.dst_id)	Action and Parameters	Status
100	myTunnel_forward(port=2)	MODIFIED
200	myTunnel_forward(port=3)	MODIFIED
default	drop()	UNCHANGED