Evolution (Feb 09 2009)


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OzzFan
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Message 864554 - Posted: 12 Feb 2009, 3:45:27 UTC - in response to Message 864526.
Last modified: 12 Feb 2009, 3:58:34 UTC

I've been using 192.168.10.0/8 for a while now. Its different enough from home networks that I don't run into problems, but still in the Class C range. Sure, you can always subnet a Class A or Class B range, but I'm keeping it simple for now.

192.168.10.0/8 grabs more address space outside the RFC-1918 space than inside, including space allocated to BBN and to Level3.


I'm unaware that any entity is entitle to 192.168.10/8 exclusively since they are supposed to be open for private use. In fact, 192.168/16 is supposed to be open and completely inside RFC1918, which would include 192.168.10/8.

Classful routing is dead, so there is no practical difference between 192.168.10.0/24 and 10.10.10.0/24.


Very true, with the exception that you have to configure subnetting manually for the Class A Address to be /24, whereas 192.168.10.0 is /24 by default since it is a Class C Address. One does not have to mess with subnetting that way.

Even so, I am working for a very small company these days, so changing the entire network to a Class A Address instead of a Class C would be quite easy. I just prefer not to do it.
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Message 864555 - Posted: 12 Feb 2009, 3:47:57 UTC - in response to Message 864552.

The 169.254.x.x block is reserved for a different purpose, and under a different RFC.


APIPA, or Automatic Private IP Addressing. Used when a host cannot find a Dynamic Host Configuration Protocol server (DHCP server). APIPA addresses are non-routable on the internet, just like all three RFC1918 classes.

... as a general rule, when I see APIPA addresses, it is a symptom of some other problem. I've never found it to be useful.

I find them to be very useful. When I see one, I start inspecting cables and switches for problems, and I have always found one.

If you disable APIPA, you generally get 0.0.0.0 instead, which is just as useful.


Except in some networks where if a DHCP server is down for a subnet, the entire subnet will default to APIPA and still be able to communicate with each other because 169.254.x.x is still a valid IP address, whereas 0.0.0.0 is not. In some cases, having APIPA can keep limited productivity for employees whereas without APIPA they're forced to call someone in to check on it sooner rather than later. Either way, its definitely a problem, one just keeps thinks moving and the other does not.

In my environment, if the DHCP server is down, I've got bigger problems, and the other stuff doesn't matter.


Indeed, each network is unique. Some network management practices work well in some environments, and not so well in others. In fact, this is one of the main reasons why I prefer not to offer advice to Matt, because what works well for my network may not be so efficient for his own setup. I think this applies to areas beyond physical network layout as well, such as the actual configuration and setup of each server.
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Message 864576 - Posted: 12 Feb 2009, 5:58:48 UTC - in response to Message 864554.


192.168.10.0/8 grabs more address space outside the RFC-1918 space than inside, including space allocated to BBN and to Level3.


I'm unaware that any entity is entitle to 192.168.10/8 exclusively since they are supposed to be open for private use. In fact, 192.168/16 is supposed to be open and completely inside RFC1918, which would include 192.168.10/8.

The 192.168.0.0 block defined in RFC-1918 is a /16.

192.168.10.0/8 includes 192.1.0.0/16 which belongs to BBN, and 192.2.0.0/16 which belongs to Level3.

I didn't look any farther, but it is perfectly okay to allocate through 192.167.255.255 and from 192.169.0.0 on up.
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Message 864652 - Posted: 12 Feb 2009, 14:58:38 UTC - in response to Message 864554.
Last modified: 12 Feb 2009, 15:00:48 UTC

... 192.168.10/8 exclusively since they are supposed to be open for private use. In fact, 192.168/16 is supposed to be open and completely inside RFC1918, which would include 192.168.10/8. ...

A slight case of reversed numbers?...

The private network block is "192.168.0.0/16" (65536 ip addresses).

The 'entire internet' is "0.0.0.0/0". A 256 ip addresses section is such as "192.168.0.0/24".

A "/8" gives (32-8)^2 = (24)^2 = 16777216 ip addresses.

The "/n" is an addressing bit mask. Hence why in another net[work bit]mask convention you get common bit masks such as 255.255.255.0 ( = "/24" ).


... And then there is ipV6. No NAT needed. But when? If ever? Do we need a deadline date such as for moving from analog to digital TV broadcasts?...

Happy surfing!
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Message 864657 - Posted: 12 Feb 2009, 15:42:15 UTC - in response to Message 864652.

A slight case of reversed numbers?...


Not reversed numbers, but my failure to move the netmask the right way, partially from being tired last night (and partially from having a very pre-occupied brain lately) when I posted.

In fact, I should have stated that I use 192.168.10.0/24, not /8. My error should have been obvious because you can't use 192.168.10/8. If you have /8 CIDR, you can only use the first octet, i.e. 192.x.x.x. 192.168.10.0/8 is too specific and would be invalid.
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Message 864867 - Posted: 13 Feb 2009, 1:01:08 UTC - in response to Message 864657.

A slight case of reversed numbers?...


Not reversed numbers, but my failure to move the netmask the right way, partially from being tired last night (and partially from having a very pre-occupied brain lately) when I posted.

In fact, I should have stated that I use 192.168.10.0/24, not /8. My error should have been obvious because you can't use 192.168.10/8. If you have /8 CIDR, you can only use the first octet, i.e. 192.x.x.x. 192.168.10.0/8 is too specific and would be invalid.

Depends on if you're trying to describe just the network, or a machine that exists on the network and the network at the same time.

After all, when you type "192.168.10.254" and "255.255.255.0" into the IP settings, you are doing just that -- entering the machine number (254) and the network number (192.168.10) at the same time.

Which I'm sure you know -- but we do have others reading along.

For the record, I use 172.20.42.0/24 for much the same reasons. I like the middle block because most everyone else uses the first one, or the last one.
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Message boards : Technical News : Evolution (Feb 09 2009)

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