[c-nsp] four L3 devices, three ports

[Mark Kent]

This is the first of what could be an annnoying sequence of questions.
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Here is the scenario:

  {ISP1}  {ISP2}

  [7301]  [7301]

  [4948]  [4948]

    {servers}

and the question is What's the best way to hook them up,
using only the three built-in gige ports?

Ignore the servers.  What I run now is this:

  {ISP1}  {ISP2}
    |        |
  [7301]-a-[7301]
    |        |
    b        c
    |        |
  [4948]-d-[4948]

a is ptp L3.
b,c,d are pruned-vlan trunks

I do ospf among the four L3 devices in the vlan,
with point-to-multipoint costs set.

Link a carries ibgp, and also is in the one ospf area.

I did this because I have this general feeling that if you've got two
edge routers then you should plug them in directly to each other,
no electronics in between.  And once I decided that, it nailed
down how to hook up the rest.  This works.

But...  I've been thinking about this:

  {ISP1}  {ISP2}
    |        |
  [7301]  [7301]
    |   \  /  |
    b    \/   c
    |   / \   |
  [4948]-d-[4948]

completely with L3 numbered ptp links (possibly not d).

Stupid?  Good?  Better than the square approach?
(I know, cisco says to avoid squares).

Thanks,
-mark