mailing list archives
splitting up a /20 (was: Class B Address)
From: William Allen Simpson <wsimpson () greendragon com>
Date: Tue, 06 Jun 2000 14:09:40 -0400
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Matt Cramer wrote:
My company has a /20 out of the traditional Class C space. We want to use
those addresses rather than the addresses our ISP would give us. We have
asked the ISP if they can announce a /24 out of that block, and they have
said "sure". However, I have read here about announcement filtering.
Will certain providers filter that /24? We have two reasons for using our
own space. First, we can get redundancy by connecting with two ISPs and
having them both announce the network (or have one announce if the other
Multi-homing redundancy is a good thing, assuming that you have undertaken
multiple service entrances to your facilities, and prevented your circuits
from being "groomed" into the same cable elsewhere. Several such concerns
have been described recently on this list.
Otherwise, your multi-homing makes no sense. Experience has shown that
failures are more likely to occur in your local facilities than in
Second, we can carve up our /20 in /24s and use them for different
Internet POPs for our company (e.g. one in the states, one in Europe, one
in the Pacific Rim, etc.).
A /20 that is split up into /24s should be filtered!
REMEMBER: IP addresses are related to network TOPOLOGY, not your company
administration. Dividing a set of "related" addresses into unrelated
topology (split by oceans) increases the routing costs of everyone else.
I am primarily a security person but unfortunately our LAN and WAN people
know less about this than I so I am trying to decide what we should do.
Any help or information about the logical design I mentioned would be
What you should do is this: look up the adjacent /20 and offer to
give them the addresses. They might make better use of them.
(I cannot tell which /20 you might be talking about, as you don't seem
to use them for your DNS, using ATT, PSI, and others instead.)
BTW: I see that your company is a major DNS polluter, registering many
business terms in .com .net and .org, and pirating the ArmstrongSucks
.com .net .org. No actual servers seem to be present.... Are there
really international .net operators that hate Armstrong? And your
company funds and hosts the discussion?
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- Re: Class B Address Matt Cramer (Jun 06)
- splitting up a /20 (was: Class B Address) William Allen Simpson (Jun 06)