RE: New Version Notification for draft-bonica-6man-frag-deprecate-00.txt

["Tony Hain" <[e-mail]>]

Mark Andrews wrote:
> One needs to get the L4 information the firewall/loadbalancer uses in
*each*
> fragment.

This is a manufactured requirement to allow devices that can't do a full
reassembly to operate in under a policy of 'verify the entire packet'.
Unfortunately, it doesn't even do that since it doesn't actually detect
overlapping fragments if it is just verifying that the L4 information is the
same. 

Load balancers just need to get over it, and use something more/other than
the L4 in the hash. The FL was intended to provide a consistent value over
the life of an L4 session, so why not use that instead of developing yet
another new option? Wait,,, that doesn't exist in IPv4, so it can't be used
because that would require learning something different...

> For UDP this is the source and destination ports.  Create a new skipable
hop-
> by-hop option that contains a copy of these values and add it along with a
> fragment header when fragmenting UDP packets.

I have no problem with that concept, but why when there are other ways of
accomplishing the task? Simply to mirror IPv4 is not a valid reason...

> 
> For TCP ensure that the IP layer informs the TCP layer if it would have to
> fragment the packet. i.e. don't send fragmented TCP packets.

So TCP is never allowed to have a long-lived session ... Or routes are not
allowed to flap. Which is it? You either tear down tcp and renegotiate mss
every time routes flap to a path with a lower mtu, or you send fragments. It
is easy to say the core is >=1500 now, but what happens with a mix of
1500/4k/9k/32k/... over the life of IPv6? Are routes never allowed to flap
with larger MTUs? Do you require every TCP implementation to do dynamic MSS,
and try to get that deployed within a decade to two?

> 
> For ICMPv6 ???
> 
> For IPv4 if DF=0 fragment the Ipv4 packet to fit in inside 1280 IPv6
packets
> destination reassembles.
> For IPv4 if DF=1 return IPv4 PTB
> 
> For XXX ????