[j-nsp] GRE on MX - weird performance issue

[Brandon Ross]

On Tue, 18 Dec 2012, Luca Salvatore wrote:

> I have a MX5 and a MX10 router connected over the Internet via a GRE 
> tunnel.  When I do a file transfer between the two sites that these 
> routers connect it looks like there is some form of rate-limiting going 
> on.  My transfer speed flat lines at about 300KB.
>
> However I know it is not a bandwidth issue because I can have multiple 
> file transfers going on at once and they all sit at about 300KB.  So 
> this shows me that I have enough bandwidth to push lots of traffic at 
> once, but each single stream of traffic never gets much faster than 
> 300KB.

This sounds like the classic example of a Bandwidth-Delay product problem. 
I suggest careful study of this page:

http://www.psc.edu/index.php/networking/641-tcp-tune

> I've tried different MTU settings on the GRE interface without much 
> change, was thinking of adjusting the MSS but can't seem to figure that 
> out on the MX.

MSS is a function of the end stations, not of a normal router, but you are 
on the right track.  Adjusting the MSS of the end stations on each side 
will help improve performance, most likely.

-- 
Brandon Ross                                      Yahoo & AIM:  BrandonNRoss
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