> What are others' opinions on this issue?

I'm actually thinking that the most desirable default behavior 
for routers is one that discourages use of SLs unless they're
explicitly configured.  So I am inclined to believe that a
router (or a multi-interface host when acting as a router) should 
by default treat every interface as if it were in a separate site,
and therefore refuse to forward SLs at all.

to enable SLs at a router the admin should have to label 
*each* separate interface with a site-id.   

similarly, hosts should not configure SLs by default.

that way, in the absence of any configuration, SLs simply don't
work at all.  apps on correctly-configured hosts aren't exposed 
to them because they aren't configured on any of their interfaces.
if any host does try to send packets to them, or source packets
from them, they don't get past the first router.

this also seems to produce the "right" behavior for people who
believe that SLs provide some security - default policy is to deny
all SL traffic, then you can explicitly decide when to permit it. 

I also think it produces the most desirable end-state should we 
reach consensus to deprecate/discourage SLs - if routers 
discourage SL by default then they'll continue to do the right
thing by default when it's generally realized that they were a
bad idea anyway, and they'll continue to be backward compatible
for those who invested in them.

Keith

p.s. actually I believe that routers should refuse to forward
SLs if they know of any route to any routable prefix, in order
to enforce the restriction that SLs should not be used except
on isolated networks.  so the above could be considered a 
fallback position.
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