Episode: 4623
Title: A brief infodump on the Broadcast Address and Routing
Source: https://hub.hackerpublicradio.org/ccdn.php?filename=/eps/hpr4623/hpr4623.mp3
Transcribed: 2026-07-31 16:15:21 (official HPR transcript)

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This is Hacker Public Radio Episode 4623, for 2026-04-22
Today's show is entitled, "A brief infodump on the Broadcast Address and Routing"
The host is Jon The Nice Guy and the duration is 00:05:46
The flag is Clean, and the license is CC-BY-SA
The summary is "Jon gives a little information on what the Broadcast address is and IPv4 Routing in general"
You are listening to a show from the Reserve Queue.
This show was submitted in March 2025 to cover occasions like this
where there are gaps in the schedule.
kind of her public radio, this is John the Nice guy.
On the HP after-minute use for January 20, 2025,
Ken, Kevin, and some girl in the internet
were talking about network dresses.
As this was part of my job for several years,
I thought so.
I'd talk about it for a couple of minutes.
All my pain networks, now years,
all we refer to as CIDR or CIDA based dressing.
Ciloft and see these expressed as slash 24,
slash 16 and so on.
This is how many ones are in the binary representation
of the local portion of this network.
Windows is one of the last remaining platforms
refer to these as net masks.
And it's expressed them as four octets
in decimal representation of those ones.
So slash 24 is 24 ones in a row or 255252550.
slash 16 is 25252550 and so on.
What does this have to do with networks and networking?
It's actually technically two pieces to this.
The first is for broadcasts or how a node
with an IPv4 address asks all the local nodes
in an IPv4 network address range
how to find other things.
The other is for routing.
But let's talk about broadcasts, right?
So back when IPv4 or just TCPIP as we knew it then
was being developed to integrate into operating systems,
most developers read the request for the comments document
about this new IPp protocol and put the address
that the device should contact to talk to all the hosts
on the local network segment or the broadcast addresses
it better known as the last available IP address in their subnet.
In a slash 24, that would be the dot 255 address in the subnet.
The engineer's at, from memory, I think it was either
some microsystems or DEC, read the same document
and call that address the network address
and made it the first available IP address on the subnet,
the dot zero.
In the end, broadcast address one out,
in the IPv4 networks and the network address was left history.
But there were at least for quite a long time,
still just enough of those legacy systems knocking around.
That it was always seen as a bit of a risk
to allow the network address back into the pool of addresses.
The broadcast address is most often seen in printer setups
or for app address requests,
but as largely been thought as largely for an out of favor,
in preference to multi-casts.
In fact, so much so, the IPv6 seems to have dropped broadcast
address entirely.
Broadcast address, rather entirely,
and uses multi-cast for almost everything now.
But why does the number of bits matter?
Now, this comes back to routing.
Routing is where a host works out
what the most specific route is to get to give an IP address.
One of the typical home network, this is fairly binary.
You have a default gateway, usually on either dot one
or dot two, five, four in your slash to any font network.
And most of the traffic goes to that.
In networks which need a higher level or HA routes are set up,
you may see up to three IP addresses being used by your router
with some method of mapping the virtual address
of the next top gateway to a physical device.
That said, even on a simple home network,
there are at least two other networks which are used.
And that's your local or loopback interface,
which is able to use all the addresses in the range,
one, two, seven, and zero, zero, zero slash eight.
But typically only binds to one, two, seven, zero, zero, one.
And the network you're connected to, which doesn't require routing.
Most hand routers use one, nine, two, one, six, eight,
zero, zero, slash, twenty, four, or one, two, one, six, eight,
one, dot zero, slash, twenty, four.
In order to work out how to get to the next top,
next top, I appear address, you're trying to reach.
The computer turns both the IP address you're trying to reach.
And all the CIDR masks in the routing table
into binary numbers, and then match is the one,
which most specifically, which is most specifically accurate,
to work out what to do with it.
So for example, if you have an IP address of 10 dot zero dot zero dot one,
then you're in that work,
slash eight, rather than your network mask is zero, zero, zero,
one, zero, one, zero.
If you're trying to find another address in that network,
you only need to match the first eight bits.
And the dress of 11 dot zero dot zero dot one doesn't match,
because the first eight bits, zero, zero, zero, zero,
one, zero, one, one doesn't match the one
of your routed network.
More specific groups will take longer to match,
which is why some other routing tables on the corner works
dedicate whole CPU cores to matching parts of the routing table.
It's also in the pre-IPV for exhaustion days.
IP addresses were typically sold in large blocks,
usually to single geographic regions.
So the only had to match a large supernet or a large block
of subnet, rather, in one go, not lots of smaller subnet.
Now once you understand this about IPV4, IPV6 works,
pretty much the same way for routing,
except the address space is four times larger,
with the number of net bits in the network area,
being 128 as opposed to IPV4's 32 bits.
I just wanna thank the janitors for triggering
this little bit of an info dump,
and I hope it's been of interest to you.
This is John the Nice guy, sign it off from HPR.
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