Access to sub network unreachable.
Simon Slater
pyevet at aapt.net.au
Sat Jan 10 12:10:18 UTC 2009
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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