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Re: Using x.x.x.0 and x.x.x.255 host addresses in supernets.
- From: James R. Cutler
- Date: Tue Jan 08 16:54:25 2008
I am astounded at seeing this discussion. I have not seen this much
disavowing of CIDR addressing since 2003 or before.
At least these arguments against .0 and .255 IPv4 addresses are based
on perceived cost of operations, not ignorance of effective network
number vs effective host number. Now, if we can get Microsoft to
really support TCP/IP, we can make much progress. Of course,
ubiquitous deployment of IPv6 will fix all that.
Especially on proxied enterprise networks, use all the addresses
available base on the effective network address having host number of
0 and the broadcast address being an effective host address of all
ones. We have had much success with this approach for some large
customer networks. Also, if your router OS works in a classful
manner, tell the vendor to fix it. We got CIDR years and years ago.
Note, the referenced Microsoft article uses the phrase, "the client
may have difficulty communicating", not will.
On Jan 8, 2008, at 4:12 PM, David Schwartz wrote:
Historically, .0 and .255 have been avoided because a lot of servers
(windows) wouldn't work using that as a host address or would flag it
as invalid if you tried to connect to it or a myriad of other
problems. Note that this was a limitation of the host, not
anything to
do with the network or any of the network equipment.
This issue has not existed with any prevelance for quite some time
and
almost everything of recent manufacture is quite happy to be assigned
in a supernet as well as on the .0 and .255 addresses.
So my oppinion is don't hesistate to use it until you find a real,
reproducible problem.
-Wayne
I have seen networks where traffic to these addresses was filtered
in an
attempt to mitigate broadcast address amplification. Typically, end
users
filter their inbound Internet traffic to their own addresses. They
know they
don't use .0 or .255 addresses and they found this is a quick way
to prevent
any nodes on their internal network from being used as amplifiers
without
having to audit/fix their entire internal network.
As we know, the "workaround" may remain in their edge router(s)
long after
it has outlived its usefulness.
A few years ago, I noticed that an ISP blocked all traffic from its
customers bound for any .0 or .255 address to prevent drones from
flooding
those addresses. I doubt this is typical, but I bet it's still
around in at
least a few places.
If you're seriously considering using these addresses, these are other
possible issue you need to consider.
DS
James R. Cutler
[email protected]
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