Subject: From: Date:

Re: [ECS] Local address masks ? Ingo Pakleppa Mon, 18 Dec 2000 21:21:07 -0800

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There are actually a number of IP addresses with special meaning:

A number of addresses are indeed reserved for private use (meaning, all 
Internet routers should refuse to forward these - you are pretty much 
guaranteed that traffic with these addresses will not go beyond your 
network). These addresses are:

one class A address:  10.x.x.x
16 class B addresses: 172.16.x.x through 172.31.x.x
255 class C addresses: 192.168.0.x through 192.168.255.x

(notice that the 192.168.x.y addresses are actually not one but 255 
separate networks - not important for your purposes, but it can throw 
somebody else a curve).

The following addresses also have special meanings (the list may not be 
complete:

127.x.x.x - any address that starts with 127 is considered a loopback 
address, and they all have the same meaning. Although typically only 
127.0.0.1 is being used, you could assign any other address, too, if your 
network is implemented properly.

224.x.x.x through 255.x.x.x are multicast IP addresses (I believe they are 
also called class D or class E, I don't remember). They are essentially not 
used at all, and intended for things like streaming audio or video 
distribution. The most important point about these addresses is that they 
would not allow bidirectional communication.

Any address that *ends* with 0 (more precisely, where the machine portion 
of the IP address is 0) identifies one network as a whole. For instance, 
address 192.168.7.0 (assuming that the subnet mask is 255.255.255.0, which 
it should be) would identify the network 192.168.7.x - you can never have a 
machine with that IP address. And any address where the machine portion is 
all 1 (for instance, 192.168.7.255 in the same example) is a broadcast 
address that allows you to send something to *all* machines on the network. 
DHCP uses that, for instance, and Microsoft networks can also use that IP 
address heavily.

Ingo

At 11:13 AM 12/18/2000 -0500, Mark Gilmore wrote:
>Hi all,
>When a LOCAL network is in use, ECS will erroneously detect an
>ISP connection if it detects ANY host address other than 127.0.0.1.
>So I was thinking that I could have ECS ignore OTHER local network
>addresses IF I new what addresses (or address "mask") were commonly
>used.
>PAUL M. said that 127.168.x.x is common.
>Would I be SAFE in ignoring this address
>(or another suggested address mask) ?
>I.E. is there a commonly-used local network address mask
>that could NEVER be used for a true ISP connection ?
>Thanks,
>--
>Mark Gilmore
>Omnipotence (ECS home automation software)
>http://omnipotencesoftware.com
>423-745-0026
>Hours: Mon-Sat, 9AM-8PM/EST

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