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Merge pull request cnp3#50 from qdeconinck/datalink
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Make a pass over the data-link technologies
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qdeconinck authored Apr 27, 2021
2 parents e0bed34 + 795ede6 commit 2dd32b9
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139 changes: 70 additions & 69 deletions exercises/lan.rst
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Expand Up @@ -10,8 +10,10 @@ Local Area Networks: The Spanning Tree Protocol and Virtual LANs

.. inginious:: stp-ports-state

.. inginious:: stp-ports-state-qcm

.. inginious:: q-stp-1

Exercises
---------

Expand All @@ -20,7 +22,7 @@ Exercises
.. figure:: /exercises/figures/ex-stp-switches.png
:align: center
:scale: 100

Fig. 1. A small network composed of Ethernet switches

2. Consider the switched network shown in Fig. 1. In this network, assume that the LAN between switches S3 and S12 fails. How should the switches update their port/address tables after the link failure ?
Expand All @@ -41,15 +43,15 @@ Exercises
\node[switch, right of=S3] (S7) {S10};
\node[switch, above of=S3] (S4) {S2};
\node[switch, below of=S3] (S9) {S4};

\path[draw,thick]
(S3) edge (S6)
(S3) edge (S7)
(S6) edge (S4)
(S3) edge (S6)
(S3) edge (S7)
(S6) edge (S4)
(S4) edge (S7)
(S3) edge (S9)
(S9) edge (S7)
(S3) edge (S7);
(S3) edge (S7);

4. Many enterprise networks are organized with a set of backbone devices interconnected by using a full mesh of links as shown in Fig.2. In this network, what are the benefits and drawbacks of using Ethernet switches and IP routers running OSPF ?

Expand All @@ -71,7 +73,7 @@ Exercises

versa


6. In the network represented in Fig. 4, can the host `H0` communicate with `H1` and vice-versa? Explain. Add whatever you need in the network to allow them to communicate.

.. figure:: /exercises/figures/ex-stp-routing_across_VLANs.png
Expand Down Expand Up @@ -99,9 +101,9 @@ Exercises
Simple network with redundant links

a. Show the messages used by the routers to discover their neighbors and establish adjacencies.

b. Show the messages that propagate the adjacencies of A during the flooding phase.

c. For each router compute its routing table once the flooding is over.

d. Consider that link `B-C` fails and that router `B` is the first to detect the failure. Router `B` will flood its updated link state packet through the entire network and all routers will recompute their forwarding table. Compute the successive updates to the routers RIB, assuming that router `C` receives the updated link-state packet from router B before detecting the failure himself.
Expand All @@ -124,19 +126,18 @@ IPMininet_ can also be used to configure the Spanning Tree protocol on Linux hos
\node[switch, right of=S9] (S7) {S7};
\node[switch, above of=S9] (S4) {S4};
\node[switch, below of=S9] (S3) {S3};

\path[draw,thick]
(S3) edge (S6)
(S3) edge (S7)
(S6) edge (S4)
(S3) edge (S6)
(S3) edge (S7)
(S6) edge (S4)
(S4) edge (S7)
(S3) edge (S9)
(S9) edge (S7)
(S3) edge (S7);


This network can be launched with the IPMininet_ script shown below. The entire
script is available from :download:`/exercises/ipmininet_scripts/stp.py`.
This network can be launched with the IPMininet_ script shown below. The entire script is available from :download:`/exercises/ipmininet_scripts/stp.py`.

.. code-block:: python
Expand All @@ -149,44 +150,44 @@ This network can be launched with the IPMininet_ script shown below. The entire
class MyTopology(IPTopo):
def build(self, *args, **kwargs):
# Switches with manually set STP priority
s3 = self.addSwitch("s3", prio=3, lo_addresses=["2001:1::4/64"])
s4 = self.addSwitch("s4", prio=4, lo_addresses=["2001:1::4/64"])
s6 = self.addSwitch("s6", prio=6, lo_addresses=["2001:1::6/64"])
s7 = self.addSwitch("s7", prio=7, lo_addresses=["2001:1::7/64"])
s9 = self.addSwitch("s9", prio=9, lo_addresses=["2001:1::9/64"])
# Hub
#hub1 = self.addHub("hub1")
# Links
self.addLink(s3, s9, stp_cost=1) # Cost changed for both interfaces
l37=self.addLink(s3, s7)
l37[s3].addParams(stp_cost=1) # cost changed for s3->s7
l37[s7].addParams(stp_cost=1) # cost changed for s7->s3
self.addLink(s9, s7) # default cost of 1
self.addLink(s6, s9)
self.addLink(s6, s4)
self.addLink(s7, s4)
super(MyTopology, self).build(*args, **kwargs)
def post_build(self, net):
for s in self.switches():
command="/usr/sbin/tcpdump -i any --immediate-mode -c 50 -w ./stp-"+s+"-trace.pcap stp"
p = net[s].popen(shlex.split(command))
super(MyTopology, self).post_build(net)
net = IPNet(topo=MyTopology())
def build(self, *args, **kwargs):
# Switches with manually set STP priority
s3 = self.addSwitch("s3", prio=3, lo_addresses=["2001:1::4/64"])
s4 = self.addSwitch("s4", prio=4, lo_addresses=["2001:1::4/64"])
s6 = self.addSwitch("s6", prio=6, lo_addresses=["2001:1::6/64"])
s7 = self.addSwitch("s7", prio=7, lo_addresses=["2001:1::7/64"])
s9 = self.addSwitch("s9", prio=9, lo_addresses=["2001:1::9/64"])
# Hub
# hub1 = self.addHub("hub1")
# Links
self.addLink(s3, s9, stp_cost=1) # Cost changed for both interfaces
l37 = self.addLink(s3, s7)
l37[s3].addParams(stp_cost=1) # cost changed for s3->s7
l37[s7].addParams(stp_cost=1) # cost changed for s7->s3
self.addLink(s9, s7) # default cost of 1
self.addLink(s6, s9)
self.addLink(s6, s4)
self.addLink(s7, s4)
super(MyTopology, self).build(*args, **kwargs)
def post_build(self, net):
for s in self.switches():
command="/usr/sbin/tcpdump -i any --immediate-mode -c 50 -w ./stp-"+s+"-trace.pcap stp"
p = net[s].popen(shlex.split(command))
super(MyTopology, self).post_build(net)
net = IPNet(topo=MyTopology())
try:
net.start()
IPCLI(net)
net.start()
IPCLI(net)
finally:
net.stop()
net.stop()
The ``addSwitch`` method creates an Ethernet switch. It assigns a random MAC address to each switch and we can configure it with a priority that is used in the high order bits of the switch identifier. We add one IP address to each switch so that we can connect to them on mininet_. In practice, IPMininet_ configures the :manpage:`brtcl(8)` software that implements the Spanning Tree protocol on Linux. We can then create the links, configure their cost if required and launch tcpdump_ to capture the Ethernet frames that contain the messages of the Spanning Tree protocol.
Expand All @@ -196,22 +197,22 @@ The network contains five nodes and six links.
.. code-block:: python
mininet> nodes
available nodes are:
available nodes are:
s3 s4 s6 s7 s9
mininet> links
s3-eth2<->s7-eth1 (OK OK)
s3-eth1<->s9-eth1 (OK OK)
s6-eth2<->s4-eth1 (OK OK)
s6-eth1<->s9-eth3 (OK OK)
s7-eth3<->s4-eth2 (OK OK)
s9-eth2<->s7-eth2 (OK OK)
s3-eth2<->s7-eth1 (OK OK)
s3-eth1<->s9-eth1 (OK OK)
s6-eth2<->s4-eth1 (OK OK)
s6-eth1<->s9-eth3 (OK OK)
s7-eth3<->s4-eth2 (OK OK)
s9-eth2<->s7-eth2 (OK OK)
By using :manpage:`brtcl(8)`, we can easily observe the state of the Spanning Tree protocol on the different switches. Let us start with ``s3``, i.e. the root of the Spanning Tree.

.. code-block:: console
mininet> s3 brctl showstp s3
s3
bridge id 0003.f63545ab5f79
Expand All @@ -223,7 +224,7 @@ By using :manpage:`brtcl(8)`, we can easily observe the state of the Spanning Tr
ageing time 300.00
hello timer 1.03 tcn timer 0.00
topology change timer 0.00 gc timer 77.90
flags
flags
s3-eth1 (1)
Expand All @@ -232,15 +233,15 @@ By using :manpage:`brtcl(8)`, we can easily observe the state of the Spanning Tr
designated bridge 0003.f63545ab5f79 message age timer 0.00
designated port 8001 forward delay timer 0.00
designated cost 0 hold timer 0.02
flags
flags
s3-eth2 (2)
port id 8002 state forwarding
designated root 0003.f63545ab5f79 path cost 1
designated bridge 0003.f63545ab5f79 message age timer 0.00
designated port 8002 forward delay timer 0.00
designated cost 0 hold timer 0.02
flags
flags
The first part of the output of the :manpage:`brctl(8)` command shows the state of the Spanning Tree software on the switch. The identifier of this switch is ``0003.f63545ab5f79`` and the root switch is itself. There is no root port on this switch since it is the root. The path cost is the cost of the path to reach the root switch, i.e. 0 on the root. Then the switch reports the different timers.

Expand All @@ -261,7 +262,7 @@ The state of switch ``s9`` is different. The output of :manpage:`brctl(8)` indic
ageing time 300.00
hello timer 0.00 tcn timer 0.00
topology change timer 0.00 gc timer 167.22
flags
flags
s9-eth1 (1)
Expand All @@ -270,23 +271,23 @@ The state of switch ``s9`` is different. The output of :manpage:`brctl(8)` indic
designated bridge 0003.f63545ab5f79 message age timer 20.00
designated port 8001 forward delay timer 0.00
designated cost 0 hold timer 0.00
flags
flags
s9-eth2 (2)
port id 8002 state blocking
designated root 0003.f63545ab5f79 path cost 1
designated bridge 0007.2a6f5ef34984 message age timer 19.98
designated port 8002 forward delay timer 0.00
designated cost 1 hold timer 0.00
flags
flags
s9-eth3 (3)
port id 8003 state forwarding
designated root 0003.f63545ab5f79 path cost 1
designated bridge 0009.7ecc45e18e5b message age timer 0.00
designated port 8003 forward delay timer 0.00
designated cost 1 hold timer 0.97
flags
flags
:manpage:`brctl(8)` also maintains a MAC address table that contains the Ethernet addresses that have been learned on each switch port.
Expand All @@ -310,7 +311,7 @@ Thanks to the traces collected by tcpdump_, we can easily analyze the messages e

.. figure:: /exercises/figures/stp-packet1.png




.. include:: /links.rst
16 changes: 8 additions & 8 deletions pkt/80211-cts.pkt
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@@ -1,11 +1,11 @@
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Control | Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Receiver Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CRC (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Control | Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Receiver Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CRC (cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
18 changes: 9 additions & 9 deletions pkt/80211-rts.pkt
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Expand Up @@ -2,13 +2,13 @@
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Control | Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Receiver Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Transmitter Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32 bits CRC |
| Frame Control | Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Receiver Address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Transmitter Address |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32 bits CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
28 changes: 14 additions & 14 deletions pkt/80211.pkt
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Expand Up @@ -2,21 +2,21 @@
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frame Control | Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address 1 (48 bits) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Address 2 (48 bits) |
| |
| Frame Control | Duration |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Address 3 (48 bits) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Sequence control |
| |
| Address 1 (48 bits) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Address 2 (48 bits) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Payload (0-2324 bytes) ~
| |
| |
| Address 3 (48 bits) +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Sequence control |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32 bits CRC |
| |
~ Payload (0-2324 bytes) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32 bits CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 changes: 2 additions & 2 deletions pkt/8021q.pkt
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Expand Up @@ -2,5 +2,5 @@
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Protocol Identifier | PCP |C| VLAN Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag Protocol Identifier | PCP |C| VLAN Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
26 changes: 13 additions & 13 deletions pkt/ip-80211.pkt
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ 802.11 header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SNAP/DSAP | SNAP/SSAP | Control | RFC 1042 |
| 0xAA | 0xAA | 0x03 | 0x00 |
| |
~ 802.11 header ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | |
| 0x800 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
~ IP packet ~
| |
| SNAP/DSAP | SNAP/SSAP | Control | RFC 1042 |
| 0xAA | 0xAA | 0x03 | 0x00 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32 bits CRC |
| Type | |
| 0x800 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| |
~ IP packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 32 bits CRC |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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