On Tue, Feb 12, 2019 at 10:26 AM Erik Kline <[email protected]> wrote: > > I think in that case it's just ensuring the MTU given to the customer > via their access link can be carried through their network without, or > which a minimum of, fragmentation. > > I finally found some text to which I was referred, in 3GPP TS 29.060 > (GTP) v15.2.0 section 13.2: > > All backbone links should have MTU values that exceeds the sum of > the maximum value plus the size of the tunnel headers (IP header, UDP > and GTP header) in order to avoid fragmentation in the backbone. > > In this case the "fit for purpose" is clearly delineated as "carrying > GTP traffic". > > I'll have to think about better text that "fit for purpose". Can we > say that network operators who can characterize effectively the MTU > requirements of traffic traversing their network should factor in > whatever overhead their operational model requires so as to minimize, > or preferably eliminate, the need for fragmentation. > Erik,
If they do that, I would hope that they include some headroom in their MTU requirements to allow for extensibility. An operator doesn't want to be stuck in a bad situation in the future when trying to deploy a new protocol, like segment routing, that is potentially considerable and highly variable overhead. Tunnels have some mitigating circumstances wrt fragmentation. Often they are used in limited domains where an operator can ensure that all the intermediate nodes properly handle fragments and the network is firewalled to limit attacks on reassembly. In such an environment, fragmentation is much more viable than on the open Internet. It still might be advantageous to limit the use fragmentation, but it's not a requirement to eliminate it completely (that may be a much harder prospect in practice). Tom > Operators that can't characterize the MTU requirements of their > customer traffic can decide if they're going to try or not, or care or > not. :-) > > On Tue, 13 Nov 2018 at 12:35, Ron Bonica <[email protected]> wrote: > > > > Hi Erik, > > > > Could you refine the recommendation a little bit? If an ISP were to ask, > > "What MTU is fit for my purpose?", how would we answer? > > > > Ron > > > > > > > Ron, > > > > > > Related to this section, at the mic I was suggesting perhaps including > > > some > > > simple text recommending that network operators SHOULD take efforts to > > > make sure the MTU(s) on their network(s) are "fit for purpose", i.e. > > > sized to > > > avoid fragmentation to the extent possible. > > > > > > I'm not sure yet how to better express that notion. It seems obvious and > > > anodyne, but it can be useful to have these things captured for reference > > > by > > > non-IETF documents. > > ***************************** > > > > _______________________________________________ > > Int-area mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/int-area > > _______________________________________________ > Int-area mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/int-area _______________________________________________ Int-area mailing list [email protected] https://www.ietf.org/mailman/listinfo/int-area
