Subject: Re: PMTUD blackhole detection, need a flag bit
To: None <email@example.com>
From: Kevin Lahey <firstname.lastname@example.org>
Date: 05/09/2001 13:20:03
In message <email@example.com>firstname.lastname@example.org writes
> i guess i need a flag bit onto a routing table, for PMTUD blackhole
> detection. the problem i have is expressed in the following comment
> * XXX: RTV_MTU is overloaded, since the admin can set it
> * to turn off PMTU for a route, and the kernel can
> * set it to indicate a serious problem with PMTU
> * on a route. We should be using a separate flag
> * for the kernel to indicate this.
> not sure if PMTUD blackhole detection is a generic sys/net problem,
> or a problem just for sys/netinet. anyway we have RTV_MTU behavior
> already in sys/net so I guess it is okay to add another bit for
> PMTUD blackhole detection.
I'm not sure what other protocols could benefit from PMTUD BHD right
now, but it certainly seems like a general, rather than IP-specific
problem. Putting new flags into the route metrics makes alot of sense
to me (but then, I wrote the comment above).
At some point, I considered having several flags -- a sort of,
"We think we've detected a black hole, and we're trying various
sized packets to see what gets through," and a "We've successfully
got packets of this size through". That seems like overkill, since
we can just turn off PMTUD on the route altogether, I guess.