An example that may be a little too contrived:
H1
|
|//
B-------A
/ // \
/ |
| |
C D
| |
| |
\ \\ /
E--------F
|\\
|
H2
A,B,C,E,F are in one site (on the left); A, D, and F are in another site (or
no site). H1 is connected to A, and H2 is connected to F.
It's fairly clear how to allow A and F to not advertise site-local
addresses across the boundary (at least, as long as it coincides with a
routing protocol boundary, e.g. OSPF area). However, if H1 knows that
H2 is witchin the same site, H1 is allowed to use its site-local source
address to send to H2's global address. However, along the H1-A-D-F-H2
path, A would have to drop the packet because it has a site-local address
and is trying to cross a site boundary.
Although this example is a bit contrived, it comes close to describing
the topology at AT&T, with Research split between the coasts and both
a private link (e.g. the internal site link) and links to the AT&T
internal network (which is still organizational-internal, so it's
reasonable to speak an IGP).
Bill
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