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- In this video I will tell you about

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run time network configuration,

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and how that works.

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So first you need to understand

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how nodes obtain an IP address.

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On servers, IP address
configuration is set statically,

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using tools like NMCLI or NMTUI.

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On workstations, IP address configuration

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typically is handed out to a DHCP server.

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DHCP is Dynamic Host
Configuration Protocol.

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That is a server that has been created by

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the owner of the network to make sure that

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if you connect to a network,
you get an IP address.

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Which is the ID that you need in order

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to communicate on the local network.

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If you wanna do troubleshooting,

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the IP command is used to set,

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and check runtime network configuration.

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When I'm talking about
runtime network configuration,

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what I mean is network configuration

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that is not persistent.

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In order to work with runtime
network configuration,

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you need to know which
tool you should use.

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Many people would say If config.

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Well I can tell you IF config is obsolete.

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It uses outdated methods for addressing

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and displaying networking,
and for that reason

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doesn't display accurate
information anymore.

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You should not use IF config,

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and on many distributions you won't

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even find IF config anymore.

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That's how it's supposed to be,

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because in the late 1990's,

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yes that's more than 20 years ago,

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the Linux network stack
has changed significantly,

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and in order to deal
with these significant

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changes, net tools was needed.

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And for that reason, IF
config is obsolete right now.

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An IP is the main command
for managing networking.

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Now here we have a demo,

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and in this demo I have listed

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the commands that you should know

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in order to troubleshoot and analyze

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your network configuration.

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Let me just demonstrate.

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So to start with I'm going to use

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sudo IP A.

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IP A in fact is short for

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IP ADDR show,

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but why would you want to type

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IP ADDR show if you can also type IP A.

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Look IP A is giving us the same.

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As you can see, we have ENS 33.

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ENS 33 is a network
interface that I am using.

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Now if you want to add
IP addresses in runtime,

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you use IP ADDR add DEV,

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followed by ENS 33 in this guys.

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And then you specify the IP address

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including the subnet mass
that you want to use.

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Uh oh. Operation not permitted.

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Is that so? Of course because
we need sudo superpowers

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in order to do something like this.

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Now if you want to verify
that this was successful,

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sudo IP A, and that will show you

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the secondary IP address has been added.

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Hey how about IF config?

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I told you that's obsolete, I know.

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But I also know that some people

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are kind of attached to it.

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The problem with IF config is that

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IF config has never been reworked

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to address the IP stack in the right way.

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So if you use sudo IF config,

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you don't see the IP
address that I just signed.

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It's here, but IF config
just cannot show it.

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And in case you really don't believe,

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lets do a man IF config and there we go.

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This program is obsolete.

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Use IP ADDR,

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IP link instead.

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That's all about IF config.

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One more thing.

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IF config is obsolete on Linux,
on all Linux distributions.

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If you are using Mac
IOS, you might confuse

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Mac IOS for Linux. It is not.

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Mac IOS is a BXD Unix distribution.

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And on that operating system
different rules apply.

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And one of these rules is that on

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Mac IOS IF config is
still the default utility.

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But this course is about Linux,

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so IP it is.

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Now if your link is down then
its not functional anymore.

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So probably direct the FURU sudo IP link,

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set ENS 33 up again.

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In some cases, this may help.

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Especially if you change
some configuration

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that needs to be rewrote.

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Next up is IP route show.

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The thing is that in IP
you have a routing table,

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and in the routing table at least

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you should have a default route.

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An IP route show allows you
to see this default route.

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In case you do not have a default route

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then you can use IP route at default via.

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But you know what, I'm
not going to do that.

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Because that would only
confuse my IP stack.

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I have a default route.

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It's working so there's
no need to change it.