implemented lab1

.gitignore

@@ -0,0 +1,2 @@
+/.vscode
+__pycache__

lab0/network_topo.py

@@ -22,13 +22,27 @@
 #!/usr/bin/python
 
 from mininet.topo import Topo
+from mininet.link import TCLink
+from mininet.node import OVSBridge
 
 class BridgeTopo(Topo):
     "Creat a bridge-like customized network topology according to Figure 1 in the lab0 description."
 
-    def __init__(self):
 
-        Topo.__init__(self)
+    def build(self):
+        hosts = []
+        for i in range(1, 5):
+            hosts.append(self.addHost(f"h{i}"))
+
+        s1 = self.addSwitch("s1", cls=OVSBridge)
+        s2 = self.addSwitch("s2", cls=OVSBridge)
+
+        links = []
+        e1 = self.addLink(hosts[0], s1, cls=TCLink, bw=15, delay="10ms")
+        e2 = self.addLink(hosts[1], s1, cls=TCLink, bw=15, delay="10ms")
+        e3 = self.addLink(hosts[2], s2, cls=TCLink, bw=15, delay="10ms")
+        e4 = self.addLink(hosts[3], s2, cls=TCLink, bw=15, delay="10ms")
+        e5 = self.addLink(s1, s2, cls=TCLink, bw=20, delay="45ms")
 
         # TODO: add nodes and links to construct the topology; remember to specify the link properties
 

lab1/Readme.md

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+# Readme
+First thing in any window: `cd share/ans-ss26-labs/lab1`
+
+In first window: `ryu-manager ans_controller.py` or `ryu-manager ryu.app.ofctl_rest ans_controller.py` to use the `SwitchFlowTester`
+
+In second window: `sudo python3 run_network.py`
+
+From second window once network runs: `xterm h1` (h2, etc) to open host terminals
+
+In second window to restart network: `exit`, then `sudo mn -c`, which also kills the controller
+
+## Common troubleshooting commands
+Ping: `h1 ping h2 -c5` , `pingall`
+
+Check TCP/UDP connectivity: `iperf h1 h2 (-u)` , add -u for UDP
+
+See flow tables on node s1: `sudo ovs-ofctl dump-flows s1` (in separate window, not mininet)
+
+# RFC things to look at
+
+[RFC Link](https://datatracker.ietf.org/doc/html/rfc1812)
+
+### Page 39: Packet Drop Action
+In the following, the action specified in certain cases is to
+silently discard a received datagram.  This means that the datagram
+will be discarded without further processing **and that the router will
+not send any ICMP error message** (see Section [4.3]) as a result.
+However, for diagnosis of problems a router SHOULD provide the
+capability of logging the error (see Section [1.3.3]), including the
+contents of the silently discarded datagram, and SHOULD count
+datagrams discarded.
+
+Das heißt: packet drop action = keine extra ICMP error message action
+
+### Page 46: TTL
+Note in particular that a router MUST NOT check the TTL of a packet
+except when forwarding it.
+
+A router MUST NOT originate or forward a datagram with a Time-to-Live
+(TTL) value of zero.
+
+A router MUST NOT discard a datagram just because it was received
+with TTL equal to zero or one; if it is to the router and otherwise
+valid, the router MUST attempt to receive it.
+
+Auf Page 65 steht auch für IP Forwarding: The forwarder decrements (by at least one)
+
+Das heißt: Jedes packet was der router (controller in unserem fall) forwarded (d.h. nicht selber schreibt) muss ttl-1 haben, aber neue pakete (z.b. ICMP echo) nicht.
+Ich glaube aber dass der router die packets schon selber dropped wenn ttl 0 ist, das müssen wir nicht extra als match action rule machen, aber kann man evtl. testen
+
+### Page 49: Router IP origin + broadcast
+When a router originates any datagram, the IP source address MUST be
+one of its own IP addresses (but not a broadcast or multicast
+address).  The only exception is during initialization.
+
+For most purposes, a datagram addressed to a broadcast or multicast
+destination is processed as if it had been addressed to one of the
+router's IP addresses;
+
+### Page 58: ICMP Echo
+A router MUST implement an ICMP Echo server function that receives
+Echo Requests sent to the router, and sends corresponding Echo
+Replies.
+
+The IP source address in an ICMP Echo Reply MUST be the same as the
+specific-destination address of the corresponding ICMP Echo Request
+message.
+
+Data received in an ICMP Echo Request MUST be entirely included in
+the resulting Echo Reply.
+
+### Page 71: Router to Router
+Das müssen wir NICHT machen, weil nur 1 router:
+
+When a router is going to forward a packet, it must determine whether
+it can send it directly to its destination, or whether it needs to
+pass it through another router.  If the latter, it needs to determine
+which router to use.  This section explains how these determinations
+are made.