Attention is currently required from: pespin.

laforge has posted comments on this change by pespin. ( 
https://gerrit.osmocom.org/c/osmo-ggsn/+/38500?usp=email )

Change subject: doc: Document MTU features in User Manual and example config 
files
......................................................................


Patch Set 5:

(2 comments)

File doc/manuals/chapters/running.adoc:

https://gerrit.osmocom.org/c/osmo-ggsn/+/38500/comment/3dfa86e0_2df359db?usp=email
 :
PS5, Line 57: When running osmo-ggsn, the user must take network Maximum 
Transmission Unit
            : (MTU) into consideration, and configure it based on network 
specific setup.
I think this is too strong a statement.  There's nothing inherently wrong with 
IP fragmentation.  It's just sub-optimal.  People operating a 2G or 3G lab 
network probably never even remotely need to worry about that, as the 
bandwidth/pps is so low.

Yes, in general, IP fragmentation is usually avoided by network administrators 
(irrespective of GTP).  But in some cases it may very well be a valid decision 
to say "no, we prefer to eat the overhead of the fragmentation if we can get an 
inner MTU of 1500 to our clients".  For example, if you use some weird protocol 
or equipment that doesn't properly handle lower MTUs, or if you are worried 
about too many problems with path MTU blackholes, etc.

So IMHO the documentation should make it clear that all of this is an 
optimization problem, not a "I must get this right to make it work at all" kind 
of topic.


https://gerrit.osmocom.org/c/osmo-ggsn/+/38500/comment/1ef51759_6533398a?usp=email
 :
PS5, Line 122: OsmOGGSN
* spelling (OsmO vs Osmo)
* TCP MSS clamping of course only works for TCP. There are other protocols out 
there that may or may not have different mechanisms.

In general, it might be a good idea to also explicitly state that if it's 
possible to increase the outer link MTU to accomodate an inner tunnel MTU of 
1500, it is much preferred over all this smaller inner MTU, MSS clamping, etc.



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