[c-nsp] Redundancy vs. Paranoia

[John Neiberger]

I'm toying around with a handful of designs and I'm trying to get a
better feel for the level of redundancy that would be considered sane so
I thought I'd check here for some opinions. The designs in question
generally deal with 6500s, 7600s, and 7200s, and the goal is to design a
redundant routing and switching system with excellent failover
characteristics. However, things can quickly get out of hand and I think
they end up becoming more complex than necessary.

Here's one of the things I'm pondering: how do I decide which is
"better", a single 6513 with dual sups and dual power supplies or two
6513s? At what point do you jump from a single box to two boxes? Does it
make sense to even bother with making two separate boxes fully
redundant?

I've got a 6513 as a core switch (L3, native IOS) and a 7513 as our
core router for WAN and mainframe connectivity. Once our need for a CIP
goes away (within a year) I've been toying with the idea of replacing
the 7513 with two 7204VXRs. I need to terminate two DS3s and an ATM T1,
so that part of the design is fairly simple.

On the other side of the room I have a single 6513 with dual sups and
my boss wants to me consider getting an additional 6513 for redundancy,
and he wants them to be designed in such a way that they are both active
for various tasks. So, now I'm faced with having multiple 6513s and
multiple 7204VXRs.

A new idea that just occurred to me is that I could replace everything
with two 7609s that would house modules for WAN connectivity and
security, and have a fiber gig module that breaks out to some high
performance 48-port 10/100/1000 switches for our data center servers.
Those switches could have an uplink to each 7609 for redundancy. I just
started pondering this new design so I haven't really thought it
through, but it might be easier to implement initially, easier to
maintain in the long run, and it would actually be a simpler, more
elegant design, which I like.

Any thoughts? How much paranoia is too much? :)  And how much
redundancy is too much?

Thanks,
John
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