2009/235 dladm Possible Values List

[James Carlson]

Garrett D'Amore writes:
> If the rest of the network is using 9000 bytes, and your device driver 
> uses a smaller value, then you'll have fragmentation or other network 
> breakage.

You usually end up with black holes, not mere fragmentation.

The nodes using the larger MTU will typically be unable to send large
packets to you, and little in the network will tell you that you've
got a problem.

(This is the well-known jumbogram issue, and is what Mike explicitly
said he doesn't need to solve.  He's interested only in solving the
"how does the user find out 'the' 'optimal' value for this driver?"
problem, and not how to make any interoperable solution.)

> I think exposing this as a single value to customers is a mistake. I 
> think knowledge of how to properly configure this value requires much 
> more advanced knowledge than we can expose in a single value -- and so 
> rightly belongs in documentation. Perhaps a man page. Perhaps a tuning 
> guide. I'm not sure, except that I feel pretty strongly that *this* is 
> *not* the right place.

As seb suggested, networking-discuss is probably a better place to
discuss the issues.  Maybe there is value in having a programmatic
interface (though I'm still wary of it), but I don't think this
project really can or should support it.

The proposals to graft it on the side look like hacks to me.

-- 
James Carlson, Solaris Networking              <james.d.carlson at sun.com>
Sun Microsystems / 35 Network Drive        71.232W   Vox +1 781 442 2084
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