github-mirror/route0
1
0
Fork 0
mirror of https://github.com/Wojtek242/route0.git synced 2024-11-23 23:45:25 +01:00
Code Issues Packages Projects Releases Wiki Activity

Editorial fixes to intro lesson

Browse Source
This commit is contained in:
Wojciech Kozlowski 2019-04-08 21:13:08 +02:00
parent 2cb1d89e77
commit a9787d6932
1 changed files with 34 additions and 25 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

59
lessons/introduction-to-route-0.md
View File

@ -16,6 +16,7 @@ communication. The convention in Route 0 is to name routers with a name that
starts with the letter `R` and hosts with a name starting with `h`. starts with the letter `R` and hosts with a name starting with `h`.
You can launch the network by running You can launch the network by running
``` ```
sudo python route0.py --topology one_rtr --scenario basic sudo python route0.py --topology one_rtr --scenario basic
``` ```
@ -27,33 +28,36 @@ addresses and default routes.
Once the CLI prompt appears let us inspect Mininet's representation of the Once the CLI prompt appears let us inspect Mininet's representation of the
network by running network by running
``` ```
net net
``` ```
in the command prompt. The output tells us about all the nodes in the network in the command prompt. The output tells us about all the nodes in the network
and the connections between them. We can see that `R1`'s `R1-eth1` interface and the connections between them. We can see that `R1`'s `R1-eth1` interface
is connected to `h1_1`'s `h1_1-eth1` interface and `R1-eth2` is connected to is connected to `h1_1`'s `h1_1-eth1` interface and `R1-eth2` is connected to
`h1_2`'s `h1_2-eth1` interface. You can visualise the network by copy-pasting `h1_2`'s `h1_2-eth1` interface. You can visualise the network by copy-pasting
the output into this [web the output into this [web
tool](https://achille.github.io/mininet-dump-visualizer/) though its usefulness tool](https://achille.github.io/mininet-dump-visualizer/) though this is of
is limited for small networks such as this. limited usefulness for small networks such as this.
## Basic IP commands ## Basic IP commands
Let us now inspect the network using some basic Linux commands. The three main Let us now inspect the network using some basic Linux commands. The three main
commands we will use to investigate the state on the nodes are `ip commands we will use to investigate the state on the nodes are `ip addr`, `ip
address`, `ip route`, and `ping`. To run any of these commands on a particular node, route`, and `ping`. To run any of these commands on a particular node, you
you need to prefix it with the node's name in the Mininet CLI. For example, to need to prefix it with the node's name in the Mininet CLI. For example, to see
see all the interfaces and their addresses on `R1` you would run all the interfaces and their addresses on `R1` you would run
``` ```
R1 ip address R1 ip addr
``` ```
There is also an older obsolete command `ifconfig` which is still commonly There is also an older obsolete command `ifconfig` which is still commonly
used. However, all information available through `ifconfig` is available used. However, all information available through `ifconfig` is available
through the `ip` commands. through the `ip` commands.
### ip address ### ip addr
This command lists all addresses assigned to the interfaces on the given This command lists all addresses assigned to the interfaces on the given
device. This includes the Ethernet address as well as all IPv4 and IPv6 device. This includes the Ethernet address as well as all IPv4 and IPv6
@ -61,7 +65,7 @@ addresses. For the purposes of these lessons we are only interested in the
IPv4 addresses which are displayed as either `x.x.x.x` or `x.x.x.x/y`. IPv4 addresses which are displayed as either `x.x.x.x` or `x.x.x.x/y`.
The first thing to notice when running this command (especially on `R1`) is The first thing to notice when running this command (especially on `R1`) is
that there are multiple IP addresses assigned to a single device. This is that there may be multiple IP addresses assigned to a single device. This is
because IP addresses are bound to network interfaces not devices. Furthermore, because IP addresses are bound to network interfaces not devices. Furthermore,
it is also possible to assign multiple IP addresses to a single interface. You it is also possible to assign multiple IP addresses to a single interface. You
will notice that the `lo` interface on `R1` actually has two IP addresses. will notice that the `lo` interface on `R1` actually has two IP addresses.
@ -69,32 +73,36 @@ will notice that the `lo` interface on `R1` actually has two IP addresses.
### ip route ### ip route
The `ip route` command is used to list all the routes installed on a particular The `ip route` command is used to list all the routes installed on a particular
node. The basic format of a route is `x.x.x.x/y via z.z.z.z` which says that node. The basic format of a route you will see at the moment is of the form
to reach the IP network `x.x.x.x/y` you must go via the address `z.z.z.z` which `x.x.x.x/y dev if-name` which means that in order to reach `x.x.x.x/y` you must
should belong to an interface on a directly connected neighbour. Note that you go via the network connected to the interface `if-name`.
won't see such routes in this network setup, because the network is too simple.
The host nodes have a default route installed which looks like `default via The host nodes have a default route installed which looks like `default via
z.z.z.z` which means that the node should route all traffic it doesn't have a z.z.z.z` which means that the node should route all traffic it doesn't have a
more specific route for via `z.z.z.z`. more specific route for via `z.z.z.z`. The IP address `z.z.z.z` should then
resolve to an interface via a routing entry like the one in the previous
paragraph. If it doesn't, the packet will fail to be forwarded.
In the network we have running you will also see routes of the form `x.x.x.x/y Another basic format of a route is `x.x.x.x/y via z.z.z.z` which says that to
dev if-name` which means that in order to reach `x.x.x.x/y` you must go via the reach the IP network `x.x.x.x/y` you must go via the address `z.z.z.z`. This
network connected to the interface `if-name`. works similarly to the default route, but is more specific. Note that you
won't see such routes in this network setup, because the network is too simple.
### ping ### ping
The command `ping` sends a special IP packet to the specified destination to The `ping` command sends a special IP packet to the specified destination to
verify connectivity with that end-host. Connectivity is verified if a response verify connectivity with that end-host. Connectivity is verified if a response
is received. Try sending a ping from `h1_1` to an IP address on `h1_2` by to the ping request is received. Try sending a ping from `h1_1` to an IP
running address on `h1_2` by running
``` ```
h1_1 ping 10.2.0.1 h1_1 ping 10.2.0.1
``` ```
The address `10.2.0.1` is the IPv4 address assigned to the interface The address `10.2.0.1` is the IPv4 address assigned to the interface
`h1_2-eth1` on `h1_2`. The command will keep pinging the specified destination `h1_2-eth1` on `h1_2`. You can check this using the `ip addr` command on
every second. To stop press `Ctrl+C`. Now try pinging the other way. The `h1_2`. The `ping` command will keep pinging the specified destination every
second. To stop press `Ctrl+C`. Now try pinging the other way. The
intermediate node `R1` knows how to forward the traffic between the two hosts, intermediate node `R1` knows how to forward the traffic between the two hosts,
because it is directly connected to both of them. because it is directly connected to both of them.
@ -103,14 +111,15 @@ because it is directly connected to both of them.
Before moving on to the next lesson it would be good to introduce a Before moving on to the next lesson it would be good to introduce a
particularly useful tool in studying networks, Wireshark, by using it to look particularly useful tool in studying networks, Wireshark, by using it to look
at pings from `h1_1` to `h1_2`. Wireshark is a tool that lets you capture and at pings from `h1_1` to `h1_2`. Wireshark is a tool that lets you capture and
inspect packets sent and received over all interfaces on a device. inspect packets sent and received over any interface on a device. Furthermore,
Furthermore, it is able to present them in a human readable form rather than it is able to present them in a human readable form rather than simply dumping
simply dumping the binary representation directly from the wire. the binary representation directly from the wire.
Start by running the command to trigger `h1_1` to send pings to `h1_2`. Now Start by running the command to trigger `h1_1` to send pings to `h1_2`. Now
open a new terminal window and navigate to the `route0` directory. We will use open a new terminal window and navigate to the `route0` directory. We will use
the `attach.py` helper script to run Wireshark on `R1` and `h1_2`. Let's start the `attach.py` helper script to run Wireshark on `R1` and `h1_2`. Let's start
with `R1` by running with `R1` by running
``` ```
sudo python attach.py --node R1 --cmd wireshark sudo python attach.py --node R1 --cmd wireshark
``` ```