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Re: Access to sub network unreachable.



On Sat, 2009-01-10 at 12:59 +1100, Simon Slater wrote:
> On Fri, 2009-01-09 at 16:56 -0800, Rick Stevens wrote:
> 
> > No, the /24 covers EITHER 192.168.0.xxx or 192.168.1.xxx, but not both.
> > To treat both as a single network you need a /23 netmask.
> > 
> > A netmask tells the system how many bits of the network address make up
> > the NETWORK part.  
> 
> This is where my misunderstanding was.
> 
> > The remaining bits make up the host identifier.  An 
> > IPV4 address is 32 bits.  A /24 (or 255.255.255.0) netmask says the 
> > first 24 bits (the first three octets) make up the network part.  
> 
> What then, is a sub-net?
> 
> > In my
> > graphic below, the netmask stuff is shown in by "x"s and the bits under
> > the "x"s make up the network address:
> > 
> > netmask:	xxxxxxxx.xxxxxxxx.xxxxxxxx.-------- (255.255.255.0 /24)
> > binary addr:	11000000.10101000.00000000.00000001 (192.168.0.1)
> > binary addr:	11000000.10101000.00000001.00000001 (192.168.1.1)
> > 
> > So you can see that they're separate networks.  Now, with a /23 netmask:
> > 
> > netmask:	xxxxxxxx.xxxxxxxx.xxxxxxx-.-------- (255.255.254.0 /23)
> > binary addr:	11000000.10101000.00000000.00000001 (192.168.0.1)
> > binary addr:	11000000.10101000.00000001.00000001 (192.168.1.1)
> > 
> > You can see here that they're the same network now, and you're using 9
> > bits as the host identifier.
> 
> Okay, for a small private network of up to 2 dozen boxes, is there a
> standard or convention for selecting the final numbering system,  eg
> 192.168.0.101 to 125 vs 192.168.9.1 to 25 ?  Is there a need to
> distinguish between computer,printer or router in the numbering
> heirarchy?
> > 
> > Also note that the netmask must be consecutive 1 bits...the first 0 bit
> > marks the end of the netmask. 255.255.254.0 is OK (the last octet is
> > 11111110 binary), but 255.255.253.0 isn't (the last octet is 11111101)
> > and would be treated the same as 255.255.255.252 (a /22 or 11111100).
> > 
> > Does it make sense now?
> 
> Getting there!
----
small network is less than 254 devices (routers, printers, computers,
servers, etc.)...should just be a class C network (subnet mask
255.255.255.0)

192.168.0.1 through 192.168.0.254

typically routers would be either top or bottom...
192.168.0.1 or 192.168.0.254

My own typical setup...

router 192.168.x.254

servers
192.168.x.1 through 192.168.x.19

printers
192.168.x.20 through 192.168.x.39

vpn/other
192.168.x.80 through 192.168.x.99

computers (dhcp)
192.168.x.100 through 192.168.x.199

miscellaneous devices (cameras, managed switches, etc.)
192.168.x.200 through 192.168.x.253

Craig


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