Can I use the first IP in a subnet, for instance 192.168.0.0?
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@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@JaredBusch said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
In my DHCP scope (for a /22 subnet), I created several address pools which omit the network and broadcast addresses, so they won't be assigned.
Even if they are in scope, those two should never be able to be assigned. It would be a broken DHCP implementation that allowed it regardless. Since hitting the broadcast should cause all the machines to respond, it would wreak havoc with your system if that happened.
How many address pools did you make? There is only one network and broadcast number.
Like @Pete-S I use a /22. I was referring to what would be a traditional network and broadcast of a /24, of which there are a few. For instance, If I have a 192.168.0.0/22, it would span 192.168.0.0-192.168.3.255. I omit 192.168.0.255, 1.0, 1.255, 2.0, 2.255 and 3.0
That is wrong, those are not network or broadcast addresses in that subnet. They are simply network addresses for hosts.
Correct. I know that. I saw something a long time ago that said that some devices can't handle those, so I blocked them out. Don't remember where, but it didn't hurt.
Maybe in the late 1990s there were still garbage services that weren't IPv4 compatible yet. But that can't possibly be the case today, no one would be able to use those things.
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@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@JaredBusch said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
In my DHCP scope (for a /22 subnet), I created several address pools which omit the network and broadcast addresses, so they won't be assigned.
Even if they are in scope, those two should never be able to be assigned. It would be a broken DHCP implementation that allowed it regardless. Since hitting the broadcast should cause all the machines to respond, it would wreak havoc with your system if that happened.
How many address pools did you make? There is only one network and broadcast number.
Like @Pete-S I use a /22. I was referring to what would be a traditional network and broadcast of a /24, of which there are a few. For instance, If I have a 192.168.0.0/22, it would span 192.168.0.0-192.168.3.255. I omit 192.168.0.255, 1.0, 1.255, 2.0, 2.255 and 3.0
That is wrong, those are not network or broadcast addresses in that subnet. They are simply network addresses for hosts.
Correct. I know that. I saw something a long time ago that said that some devices can't handle those, so I blocked them out. Don't remember where, but it didn't hurt.
Maybe in the late 1990s there were still garbage services that weren't IPv4 compatible yet. But that can't possibly be the case today, no one would be able to use those things.
That's good that is no longer a thing.
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@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@JaredBusch said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
In my DHCP scope (for a /22 subnet), I created several address pools which omit the network and broadcast addresses, so they won't be assigned.
Even if they are in scope, those two should never be able to be assigned. It would be a broken DHCP implementation that allowed it regardless. Since hitting the broadcast should cause all the machines to respond, it would wreak havoc with your system if that happened.
How many address pools did you make? There is only one network and broadcast number.
Like @Pete-S I use a /22. I was referring to what would be a traditional network and broadcast of a /24, of which there are a few. For instance, If I have a 192.168.0.0/22, it would span 192.168.0.0-192.168.3.255. I omit 192.168.0.255, 1.0, 1.255, 2.0, 2.255 and 3.0
That is wrong, those are not network or broadcast addresses in that subnet. They are simply network addresses for hosts.
Correct. I know that. I saw something a long time ago that said that some devices can't handle those, so I blocked them out. Don't remember where, but it didn't hurt.
Maybe in the late 1990s there were still garbage services that weren't IPv4 compatible yet. But that can't possibly be the case today, no one would be able to use those things.
That's good that is no longer a thing.
Yeah, can't have been for a really long time. Since nearly everyone, especially outside of the SMB, has been using non-/24 for decades now, they'd run into it constantly. And since it causes a "not compatible with the Internet protocol" issue, it's hard for anyone to defend it
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@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
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@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
Yeah, 10Base-T and BNC was early 1990s. By 1997 we were already way, way past that stuff even in small, cheap deployments.
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@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
Yeah, 10Base-T and BNC was early 1990s. By 1997 we were already way, way past that stuff even in small, cheap deployments.
I finally got to retire that thing last year.
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@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
Yeah, 10Base-T and BNC was early 1990s. By 1997 we were already way, way past that stuff even in small, cheap deployments.
I finally got to retire that thing last year.
What? WTF was it hooked to?
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@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
Yeah, 10Base-T and BNC was early 1990s. By 1997 we were already way, way past that stuff even in small, cheap deployments.
I finally got to retire that thing last year.
What? WTF was it hooked to?
They make BNC to RJ 45 adapters
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@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
Yeah, 10Base-T and BNC was early 1990s. By 1997 we were already way, way past that stuff even in small, cheap deployments.
I finally got to retire that thing last year.
What? WTF was it hooked to?
A dot matrix printer that printed checks from our ERP system. I got a brand new identical replacement printer (when the original one was dying) that had an ethernet port and the VAR couldn't get it to work properly. So, I had to end up connecting it back to the ancient directjet via centronics. My new switches didn't support 10Base-T, so I had to setup a 5-port switch and connect it to that. PITA.
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@JaredBusch said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
Yeah, 10Base-T and BNC was early 1990s. By 1997 we were already way, way past that stuff even in small, cheap deployments.
I finally got to retire that thing last year.
What? WTF was it hooked to?
They make BNC to RJ 45 adapters
This one actually had both connectors. I just used the RJ45.
Edit: It was similar to this one, but mine had 3 parallel ports.
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@Pete-S said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
Is it possible / bad practice to use the first address in the network, for instance 192.168.0.0 (netmask 255.255.255.0) ?
If I remember correctly a long time ago it wasn't possible but nowadays it is. I never use it but when you have small subnets like /29 it could be nice.
@Pete-S : The short answer is No. The longer answer is that it depends on the math.
In 192.168.0.0/24, 192.168.0.0 is the network address... 192.168.0.255 is the broadcast address.
In a 192.168.0.0/23, 192.168.0.0 is the network address, and 192.168.1.255 is the broadcast address.... 192.168.1.0 is a usable IP address in that network.
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@dafyre said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@Pete-S said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
Is it possible / bad practice to use the first address in the network, for instance 192.168.0.0 (netmask 255.255.255.0) ?
If I remember correctly a long time ago it wasn't possible but nowadays it is. I never use it but when you have small subnets like /29 it could be nice.
@Pete-S : The short answer is No. The longer answer is that it depends on the math.
In 192.168.0.0/24, 192.168.0.0 is the network address... 192.168.0.255 is the broadcast address.
In a 192.168.0.0/23, 192.168.0.0 is the network address, and 192.168.1.255 is the broadcast address.... 192.168.1.0 is a usable IP address in that network.
No that’s not how that works. The first address in a subnet is never usable. The last address in a subnet is never usable. There is no in between. Every single subject has exactly one first address and exactly one last address.
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@JaredBusch said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@dafyre said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@Pete-S said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
Is it possible / bad practice to use the first address in the network, for instance 192.168.0.0 (netmask 255.255.255.0) ?
If I remember correctly a long time ago it wasn't possible but nowadays it is. I never use it but when you have small subnets like /29 it could be nice.
@Pete-S : The short answer is No. The longer answer is that it depends on the math.
In 192.168.0.0/24, 192.168.0.0 is the network address... 192.168.0.255 is the broadcast address.
In a 192.168.0.0/23, 192.168.0.0 is the network address, and 192.168.1.255 is the broadcast address.... 192.168.1.0 is a usable IP address in that network.
No that’s not how that works. The first address and a subnet is never usable. The last address and a subnet is never usable. There is no in between. Every single subject has exactly one first address and exactly one last address.
That is what he is saying. The network is 192.168.0.0, so 192.168.1.0 is usable.
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@JaredBusch said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@dafyre said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@Pete-S said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
Is it possible / bad practice to use the first address in the network, for instance 192.168.0.0 (netmask 255.255.255.0) ?
If I remember correctly a long time ago it wasn't possible but nowadays it is. I never use it but when you have small subnets like /29 it could be nice.
@Pete-S : The short answer is No. The longer answer is that it depends on the math.
In 192.168.0.0/24, 192.168.0.0 is the network address... 192.168.0.255 is the broadcast address.
In a 192.168.0.0/23, 192.168.0.0 is the network address, and 192.168.1.255 is the broadcast address.... 192.168.1.0 is a usable IP address in that network.
No that’s not how that works. The first address in a subnet is never usable. The last address in a subnet is never usable. There is no in between. Every single subject has exactly one first address and exactly one last address.
He pointed that out.
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@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@JaredBusch said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@dafyre said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@Pete-S said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
Is it possible / bad practice to use the first address in the network, for instance 192.168.0.0 (netmask 255.255.255.0) ?
If I remember correctly a long time ago it wasn't possible but nowadays it is. I never use it but when you have small subnets like /29 it could be nice.
@Pete-S : The short answer is No. The longer answer is that it depends on the math.
In 192.168.0.0/24, 192.168.0.0 is the network address... 192.168.0.255 is the broadcast address.
In a 192.168.0.0/23, 192.168.0.0 is the network address, and 192.168.1.255 is the broadcast address.... 192.168.1.0 is a usable IP address in that network.
No that’s not how that works. The first address in a subnet is never usable. The last address in a subnet is never usable. There is no in between. Every single subject has exactly one first address and exactly one last address.
He pointed that out.
Yes in a very confusing way by starting off the short answer is......
There is only one answer to the question
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OK, I did some more research and made some test. I believe most people got this one wrong and for reasons that are historical.
Assume we have the network 192.168.1.0/24.
Subnet mask 255.255.255.0. The address range is 192.168.1.0 to 192.168.1.255.192.168.1.0 is a valid host IP - contrary to what most people believe.
192.168.1.255 is reserved for directed broadcast.Why?
An IP like 192.168.1.0 used to be excluded from use by a host in the past. This was obsoleted in conjunction with the introduction of classless subnets, CIDR. Mentioned in 1995, RFC 1878, which also obsoleted something related, which was the exclusion of certain subnets called subnet zero and the all-ones subnet.
In the past IPs like 192.168.1.0 has also been used as a broadcast address but that practice is also obsolete. RFC 1812 (also 1995) states that 192.168.1.255 should be used for directed broadcast in the 192.168.1.0/24 network and that 192.168.1.0 is forbidden to use for that purpose.
Problem when something becomes obsolete is that you still have old equipment, old protocols and old habits in use. So it takes many years before you can actually stop doing certain things that were needed in the past.
To test the state of things today I spun up some VMs. I used 172.16.0.0/24 as my network.
No problem setting 172.16.0.0 as IP address on CentOS or Debian for example. Everything works as you would expect.
You could however see some remnants of the past, like this:
As mentioned above, it was a long time since that was considered a broadcast address.Windows 7 was however another story. You can't enter 172.16.0.0 as a valid IP address in network settings. But you can do it on the command line with netsh. And then it shows up as expected. Network works as expected too.
So all in all, it is technically OK to use the first IP as an host IP. It's not reserved anymore and hasn't been for more than two decades. Protocols that used that IP for broadcast or reserved for the network address are not in use anymore.
The biggest risk is probably to run into applications where they on purpose don't allow you to enter a specific "invalid" IP address.
That said, it would probably be very confusing for most people.
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Another fun little tidbit is that when you get to small size network such as /31 (2 IP addresses) then there are no broadcast address and of course no network address. RFC 3021 from year 2000 - for point to point links.
I wonder if Windows 7 for instance would complain in the GUI trying to enter that...
Update: Of course it didn't work in Windows 7 GUI either.
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@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@wrx7m said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
@scottalanmiller said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
1990s there were still garbage services
I do remember that I was not able to change the SNM on an old HP jetdirect print server that we had connected to some dot matrix printers via centronics connectors. It was 10base-T and also had a BNC connector on it.
Yeah, 10Base-T and BNC was early 1990s. By 1997 we were already way, way past that stuff even in small, cheap deployments.
I finally got to retire that thing last year.
What? WTF was it hooked to?
Seriously? I had a wide cartridge dot matrix printer in use until last year that had that same HP jet direct box. The printer had a centronix connector on it. In fact I just gave the printer to a client because I couldn't sell it. Instead of just trashing it, I gave it to a client who had the same printer - so now they have a backup.
I'm guessing most of those dot matrix printers sold today have built in NICs, but even 10 years ago I could and did buy dot matrix that had parallel ports on them instead of built in NICs.
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@Pete-S said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
Another fun little tidbit is that when you get to small size network such as /31 (2 IP addresses) then there are no broadcast address and of course no network address. RFC 3021 from year 2000 - for point to point links.
I wonder if Windows 7 for instance would complain in the GUI trying to enter that...
Update: Of course it didn't work in Windows 7 GUI either.
Interesting about the no broadcast addresses - at what point are broadcasts addresses dropped from CIDR notation?
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@Pete-S said in Can I use the first IP in a subnet, for instance 192.168.0.0?:
Another fun little tidbit is that when you get to small size network such as /31 (2 IP addresses) then there are no broadcast address and of course no network address. RFC 3021 from year 2000 - for point to point links.
Good point.
