Charter ARP Leak

John Kristoff jtk at
Mon Jan 5 17:28:00 UTC 2015

On Mon, 29 Dec 2014 14:23:56 -0500 (EST)
Jay Ashworth <jra at> wrote:

> From an intermediate routing standpoint, though, it would be easier
> to add an *adjacent* block, not one halfway across the address space,
> no?

One never knows how the address space is carved up.  Changing what
were once deemed reasonable addressing ideas, ultimately becoming
grossly suboptimal, often loses out to competing interests.

A long time ago, I arrived at a network where there were two major
sites with many LANs at each site. Generally speaking each LAN was a
department, but a department spanned both sites.  Each department/LAN
at a site started off with less than a /25 worth of nodes.

This was apparently all done at a time when RIPv1 was the norm and
multiple subnet sizes were not widely deployed if even available in the
gear deployed.

The arrangement I inherited was such that a department was assiged
a /24, with the lower half (a /25) network at one site, and the upper
half at the other.  As long as the organization's assigned /16 always
used /25's per network and departments split between sites fit into
the /25 things might have been fine for awhile. By the time I arrived
the address space was impossibly fragmented with some router
interfaces having many secondaries as departments arose, grew, split,
ceased to exist and new sites came online.  This had the now
predictable effect of turning a seemingly nice day one addressing plan
into a fragmented and secondary mess. That was over 15 years
ago and there are still remnants of the originally addressing plan in

I wouldn't be too surprised or even too concerned about these sorts of
configurations that appear poorly designed in hindsight. They are
natural for most any complex system as it evolves.  It is all part of
the fun.


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