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Re: Access to sub network unreachable.



On Fri, 2009-01-09 at 21:07 -0700, Craig White wrote:
> 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
> 
Thanks, these are the sort of guides I was after.

-- 
Hooroo,
Simon
Registered Linux User #463789. Be counted at: http://counter.li.org/



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