Special Purpose IP Addresses
Video Activity
Join over 3 million cybersecurity professionals advancing their career
Sign up with
Required fields are marked with an *
or
Already have an account? Sign In »
Video Transcription
00:00
>> Now that we've covered some of
00:00
the basics of IP addressing,
00:00
the next thing I want to talk about is
00:00
the specific IP addresses
00:00
that are set apart for particular use.
00:00
The first set of IP addresses that we'll talk
00:00
about is one called RFC 1918.
00:00
If you'll remember from earlier,
00:00
RFCs contain the rules and
00:00
specifics of the TCP IP protocol.
00:00
What's been amendments to the protocol throughout
00:00
the years is a specific set
00:00
of IP addresses that are
00:00
determined to be just for internal use.
00:00
Meaning that if these addresses
00:00
appear out on the Internet,
00:00
the Internet routers to drop packets.
00:00
All my internal network,
00:00
I will almost always see an IP address on
00:00
the Ten Network or the 172.16
00:00
network through the 172.31
00:00
network or something on the 192.168 network.
00:00
Again, those are reserved just for internal devices.
00:00
The second bullet must be behind a NAT device.
00:00
NAT stands for network address translation.
00:00
If we have these private addresses
00:00
that can't go out in the Internet,
00:00
that's a problem because
00:00
my host need to go out on the Internet
00:00
and that's okay because
00:00
we have network address translation,
00:00
which essentially hides our internal IP addressing,
00:00
and allows our IP addresses that are going out to
00:00
the Internet to present with a different source address,
00:00
a public source address that's been
00:00
received from our Internet service provider.
00:00
We'll talk about that later
00:00
but I just want you to know if you're thinking
00:00
about how can I get on
00:00
the Internet? All of that is resolved.
00:00
This is behind your router
00:00
and it's a security benefit that you
00:00
have a set of internal IP addresses
00:00
that can't be routed on the Internet.
00:00
There's also a loopback address, which is 127.0.0.1.
00:00
Ultimately, sometimes you refer to it
00:00
as home because we mean my computer.
00:00
When I bing 127.0.0.1,
00:00
that's really testing my network card to
00:00
make sure that it can send and receive data.
00:00
Every now and then you have
00:00
that issue that you just can't figure out.
00:00
It never hurts to make sure that
00:00
your NIC is sending and receiving properly.
00:00
APIPA addresses.
00:00
Automatic IP addressing is what APIPA stands for.
00:00
When we're configured to get
00:00
an IP address from a DHCP server,
00:00
we talked about this in Chapter 1.
00:00
Client comes online and
00:00
send out a discovery message that says,
00:00
''Hey, is anybody out there on the DHCP server?''
00:00
The DHCP servers are going to offer an IP address.
00:00
We're going to respond and
00:00
acknowledge that the whole door of
00:00
phase we discussed with the DHCP section.
00:00
But what if the client sends out
00:00
the broadcast says, ''Hey,
00:00
is there anybody is a DHCP server and nobody answers?.
00:00
What if there is no DHCP server available?
00:00
That's okay because the client will auto configure
00:00
an IP address beginning with 169.254 something something.
00:00
That is much better than the way it used to be.
00:00
Back in the early Windows 98 days,
00:00
if a client couldn't get
00:00
an IP address from a DHCP server,
00:00
the address would be 0.0.0.0,
00:00
and you can't do anything on
00:00
the network with that type of address.
00:00
At least now client's auto configure
00:00
with this 169.254 address.
00:00
The DHCP server is down for everybody,
00:00
we can at least have some local communication.
00:00
That's a good step in
00:00
the right direction and that's referred to
00:00
as a APIPA address.
00:00
We've already talked about the network ID.
00:00
We said the network ID is an IP address
00:00
with the full host portion all set to zero.
00:00
We've also said that we don't assign
00:00
that network ID to any particular device,
00:00
but we do use it to summarize the network.
00:00
We might use it on access control lists,
00:00
on routers to describe a pathway to a certain route.
00:00
We might use it on firewalls to say
00:00
block all traffic to a particular network,
00:00
but it does not go to a specific device.
00:00
It's there to summarize.
00:00
We also have unicasting, multicasting, and broadcasting.
00:00
Unicasting is what we see the most and that's from
00:00
a single host going out to a one-to-one communication.
00:00
In this illustration,
00:00
I'm going from 172.16.4.1-172.16.4.253.
00:00
That's a one-to-one communication and that's unicasting.
00:00
If we have something like a video conference that
00:00
certain hosts are participating in or if we're
00:00
sending out an image of a Windows system only to
00:00
Windows devices might use a multicast.
00:00
Essentially the clients will have to have
00:00
special software to login to get
00:00
their multicast address and
00:00
describe to this group but it is a way we can
00:00
send them the same message or data to multiple computers.
00:00
Broadcasting goes to every host on a subnet.
00:00
The broadcast address is going to be
00:00
the network ID plus the host portion also to binary ones.
00:00
In this case, if you look at the diagram on the left,
00:00
we see a broadcast from the source to the destination.
00:00
What I would assume by looking at this is they're
00:00
using a 24-bit subnet mask and not
00:00
using the standard Class B address 172.16.4.255.
00:00
The 255 indicates all hosts on the subnet,
00:00
so the broadcast address is when
00:00
all hosts are said to binary ones.
00:00
Remember that your IP address is a client can't have
00:00
the host is all binary zeros or all binary ones.
00:00
Those are addresses that are reserved.
00:00
Special IP addresses.
00:00
What I want you to take away from this is
00:00
the 1918 private internal addresses,
00:00
the Ten Network, 172.16-172.31
00:00
and 192.168, the loopback address.
00:00
The entire range of 127 is
00:00
reserved for troubleshooting but specifically,
00:00
the loopback is often used as
00:00
127.0.0.1 and it's to test out your network.
00:00
We have network IDs which are used
00:00
to identify the network for routers,
00:00
firewalls, and whatever purpose
00:00
we need to summarize the network.
00:00
We then talked about APIPA addresses.
00:00
Anytime on the tests that you see a host with
00:00
a 169.254 address,
00:00
you know that it's trying to get an IP address from
00:00
DHCP but DHCP is not available.
00:00
That very well may be the problem in
00:00
question they're asking you to troubleshoot.
00:00
Finally, we have unicast,
00:00
one-on-one communication, multicast, one-to-many,
00:00
and broadcast, one to all.
00:00
Remember the broadcast address is going to be
00:00
the network ID plus all the host bits set to binary ones.
Up Next
Similar Content
