RINA - scott whaps at the nanog hornets nest :-)

Sat Nov 6 21:52:26 UTC 2010

> 
> He was referring to the updated RFC 4821.
> 
> " In the absence of ICMP messages, the proper MTU is determined by
> starting
>     with small packets and probing with successively larger packets.
> The
>     bulk of the algorithm is implemented above IP, in the transport
> layer
>     (e.g., TCP) or other "Packetization Protocol" that is responsible
> for
>     determining packet boundaries."
> 
> It is designed to support working without ICMP. It's draw back is the
> ramp time, which makes it useless for small transactions, but it can
be
> argued that small transactions don't need larger MTUs.
> 
> 
> Jack

That is also somewhat mitigated in that it operates in two modes.  The
first mode is what I would call "passive" mode and only comes into play
once a black hole is detected.  It does not change the operation of TCP
until a packet disappears.  The second method is the "active" mode where
it actively probes with increasing packet sizes until it hits a black
hole or gets an ICMP response.