Its funny, I read the list faithfully, but go months without having anything to say or ask. And then come three things in a row!
A friend asked for help, and when I looked at his (business) setup I found the following.
One moderate spec machine, now a few years old and in need of renewal, with two network cards. One card is DHCP to the one-port router, which goes to the ADSL connexion, which is fairly lightly used. This is getting an address in the range 192.168.0.x, as usual.
the other card is set up for static addressing, runs off an independent hub, and its using the range 172.16.0.1, with a subnet mask of 255.255.0.0.
I was all set to find that there was some huge network behind this, but in fact all there is is two printers. Yes, this network has one computer and two printers and appears to be using an internal Class B address for it, if I understand the situation correctly.
This was set up by a local computer store after apparently a great deal of head scratching.
Well, I too am scratching my head and trying to figure out could anyone have a legitimate reason (ie not simply they failed to understand networking) for doing this. Like, if I really wanted to have the two printers on a separate net, why not just use a subnet mask of 255.255.255.128 and get two subnets that way? But in any case, why make life complicated with subnets, why would I not just assign them addresses in the 192.168.0.x range. What I usually have done in these situations (but I'm an amateur at this stuff nowadays) is put the printer on a static address of 192.168.0.100, have the router assign addresses to the computers in the low numbers, and everyone seems to print just fine. There are only two printers and one computer here, so what could the problem be?
It seems that the simplest thing to do is take all this stuff out and use a 5 port router/modem, and just make the two printers 101 and 102, why would this not work?
Is this missing something obvious?
Cheers
Al
the other card is set up for static addressing, runs off an independent hub, and its using the range 172.16.0.1, with a subnet mask of 255.255.0.0.
Could there be a historical reason - could the computer that has two network cards originally only have the 172 one and a modem dial up address, that over time was upgraded (without any thought to the overall network structure), maybe first to a usb-adsl modem, then to a router. Someone not understanding might have gone "oh the router dosnt support the 172 address range" and :. without looking at the other networkand whether the printers could be moved, just added a new network card.
James
James Taylor wrote:
Could there be a historical reason
Another possibility is that the printers came from a different environment (eg second hand from a large office) and came pre-configured with 172.* addresses, and nobody knows how to change the IP addresses in the printers.
Peter Alcibiades wrote:
One moderate spec machine, now a few years old and in need of renewal, with two network cards. One card is DHCP to the one-port router, which goes to the ADSL connexion, which is fairly lightly used. This is getting an address in the range 192.168.0.x, as usual.
the other card is set up for static addressing, runs off an independent hub, and its using the range 172.16.0.1, with a subnet mask of 255.255.0.0.
I was all set to find that there was some huge network behind this, but in fact all there is is two printers. Yes, this network has one computer and two printers and appears to be using an internal Class B address for it, if I understand the situation correctly.
This is commonplace for people that don't fully understand the subnets, they see that there is a class B range on 172.16.0.0 and for some reason assume that it is mandatory that this needs to be a class B subnet, also I think a lot of GUI network configuration stuff will actually default to that if you specify an address in the class B range.
The same people moan at me for operating a class C range on 10.200.0.0 at home (mostly to avoid some clients internal subnets so I don't run into routing issues with VPN's) , stating that it should be class A
Like, if I really wanted to have the two printers on a separate net, why not just use a subnet mask of 255.255.255.128 and get two subnets that way? But in any case, why make life complicated with subnets, why would I not just assign them addresses in the 192.168.0.x range. What I usually have done in these situations (but I'm an amateur at this stuff nowadays) is put the printer on a static address of 192.168.0.100, have the router assign addresses to the computers in the low numbers, and everyone seems to print just fine. There are only two printers and one computer here, so what could the problem be?
It seems that the simplest thing to do is take all this stuff out and use a 5 port router/modem, and just make the two printers 101 and 102, why would this not work?
Yes for that size network I would agree. The consumer grade of router tends to struggle if ask the NAT to deal with two many hosts on the private side but for such a small number of machines it would be fine.
I think in this case the most likely thing is that the 172.16.0.0 network already existed and then they added the router, not really knowing what was going on and rather than put one in the others range they ended up with the above arrangement. That or possibly the system was originally on a no-nat broadband service so they could only have one address on the "public" NIC.
Is this missing something obvious?
Not that I can see...believe me I have seen this and worse many times (including the recent new client who has a "private" subnet starting at 11.22.33.0)
I think in this case the most likely thing is that the 172.16.0.0 network already existed and then they added the router, not really knowing what was going on and rather than put one in the others range they ended up with the above arrangement. That or possibly the system was originally on a no-nat broadband service so they could only have one address on the "public" NIC.
This is my thoughts exactly - the number of "technicians" who operate a "dont understand it + its working = leave it alone" isn't always a good thing ... before you know it: http://sysadminday.com/images/horror/Backbone.jpg
Is this missing something obvious?
Not that I can see...believe me I have seen this and worse many times (including the recent new client who has a "private" subnet starting at 11.22.33.0)
Before "internet access" really became common, there where lots of places which that did non standard ip addresses - I think a lot of people had upgraded from various network architectures (Netboi, ethernet, token ring etc) and without looking into any specs of IP, they understood the principles of subnets and just picked random numbers for their private networks.
Oh the difficulty some of these manufacturers had when they decided to give connectivity to all workstations, and realized that basically every machine (industrial machines as well as computers) had to be changed from their static addresses because they had just made 1/256th (or more) of the internet disappear from their sights.
James
James Taylor wrote:
This is my thoughts exactly - the number of "technicians" who operate a "dont understand it + its working = leave it alone" isn't always a good thing ... before you know it: http://sysadminday.com/images/horror/Backbone.jpg
On the other hand, the adage "If it aint broke, don't fix it" is often relevant! :-) Steve
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James Taylor -
Mark Rogers -
Peter Alcibiades -
steve-ALUG＠hst.me.uk -
Wayne Stallwood