Security Basics mailing list archives

[OT] IP Address scheme for branch office


From: martin <martiniscool () gmail com>
Date: Wed, 11 Nov 2009 12:12:48 +0000

Hi All

this isn't really a security quesiton, more of a network question, but
I hope somebody can help.  I'm working in an environment where the
network designe was inherited from people who were here a long long
time before I started !!  Obviously the network design is dated and
neets a bit of a re-think

Currently, we have WAN links to all of our branch office.  The WAN
links are MPLS links which are managed by a 3rd party.  Currently we
have 10 24-bit subnets assigned to each office.  eg,
192.168.0.0/24-192.168.9.0/24 is assigned to office 1,
192.168.10.0-192.168.19.0/24 is assigned to office 2 etc.  Each one of
the 10 subnets is for a specific purpose, eg subnet 5 is for desktops
(in the second example it would be subnet 15 etc), 9 is for guests etc
etc.

Additionally, now we'd like to segment the network further in each
branch and create a separate segment for servers etc.  The problem
with the design above, is that there's no easy way to route all the
subnets for a particular office using just one route.  Additionally,
each time we need to setup a new subnet at a branch office, we have to
get the MPLS provider to add a new route for that subnet.  I know we
could set up the routes for all 10 offices in advance, but for reasons
too difficult to explain here, we don't want to go down that route !!

The easiest way (that I can see) of re-designing the network to
minimize the routes is to give each office 8 24-bit subnets instead of
10.  Then we can cover each office with one route using a /21 route on
the MPLS routers.  The problem with this, is that each office will no
longer have a "5" subnet - the first office will have 192.168.0.0/24 -
192.168.7.0/24, the second office will have
192.168.8.0/24-192.168.15.0/24 but the 3rd will have 192.168.16.0-23
... so there's no 5 subnet !!

The reason we like to keep certain subnets for different usage is to
make it easier for our helpdesk staff to remember.

I'd appreciate any suggestions anybody has on how to make this eaiser,
or how you do this in your own environment

Thanks in advance
M

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