Hi Joe, > -----Original Message----- > From: Joe Touch [mailto:[email protected]] > Sent: Friday, June 17, 2016 11:19 AM > To: Templin, Fred L <[email protected]>; Vincent Roca > <[email protected]> > Cc: [email protected]; [email protected] > Subject: Re: [Int-area] Comments for draft-ietf-intarea-tunnels-02 > > > > On 6/17/2016 10:32 AM, Templin, Fred L wrote: > > Hi Vincent, > > > > Although Joe and I may not agree on all points (yet), I am pretty sure that > > one point we do agree on is that tunnels will ultimately need to account for > > fragmentation of one form or another. Without fragmentation, nested > > tunnels within tunnels can only recurse so far until an MTU underrun > > is encountered. And, without fragmentation, tunnels cannot support a > > minimum MTU if they traverse links with sufficiently small MTUs even > > if there is no nesting. > Yup.
It has taken a long time for us to bring this realization to the community, but I think we are coming to a consensus understanding. > > It is true that one possibility is for the tunnel to simply shut down if it > > encounters an MTU underrun meaning that one or more destinations > > will simply become unreachable. But, that sort of arrangement may not > > be acceptable for safety-critical communications where destinations > > should be made reachable through any means available. > Yes - this is the only end-run that seems to work within the constraints > of existing specs. It does have a downside, though - it basically works > like "the tree in the forest". Until it actually falls, there's no point > in preventing its use. However, once it falls, it cannot get "back up" > again - if it did, it would act like a link that requires a different MTU. > > So it's "optimistic" with a fairly bad failure mode. IMO, its' the only > safe way to deploy non-reassembling tunnels, even in a "controlled" > environment -- because "controlled" is only true as long as it can be > known, and the "shut-down" approach serves a a monitor to enforce that > control. As an eternal optimist, that kind of failure mode really bums me out. We definitely can't use it for airplane comms where we have to ensure safety of flight even over data links that have sub-Mbps throughput and hence fragmentation may be the only option. But, I guess in other environments if you hit the MTU wall there is no choice but to go belly-up... Thanks - Fred [email protected] > Joe _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
