[plug] Modem MRU setting and VPN dropouts

[Lucas van Staden]

Hi,

I have had an interesting issue, and solved it (for now) by adjusting 
the MRU setting on my modem.
And I don't really understand why...
I have googled a bit, but cannot find a clear answer to why this helped.

Ok, so the issue:

I connect a vpn to my work servers. Since yesterday, the VPN drops as 
soon as I try and push large data accross (in this example I am doing a 
svn commit)

Dec 22 07:28:18 multivac pppd[5406]: Plugin 
/usr/lib/pppd/2.4.5//nm-pptp-pppd-plugin.so loaded.
Dec 22 07:28:18 multivac pppd[5406]: pppd 2.4.5 started by root, uid 0
Dec 22 07:28:18 multivac pppd[5406]: Using interface ppp0
Dec 22 07:28:18 multivac pppd[5406]: Connect: ppp0 <--> /dev/pts/1
Dec 22 07:28:22 multivac pppd[5406]: CHAP authentication succeeded
Dec 22 07:28:22 multivac pppd[5406]: MPPE 128-bit stateless compression 
enabled
Dec 22 07:28:24 multivac pppd[5406]: local  IP address 10.0.105.36  Dec 
22 07:28:24 multivac pppd[5406]: remote IP address 10.0.105.72  Dec 22 
07:28:24 multivac pppd[5406]: primary   DNS address 10.0.16.10
Dec 22 07:28:24 multivac pppd[5406]: secondary DNS address 10.0.32.30

Here I tried to do a vpn commit

Dec 22 07:29:18 multivac pppd[5406]: Modem hangup
Dec 22 07:29:18 multivac pppd[5406]: Connect time 0.9 minutes.
Dec 22 07:29:18 multivac pppd[5406]: Sent 7467 bytes, received 118449 
bytes.
Dec 22 07:29:18 multivac pppd[5406]: Connection terminated.
Dec 22 07:29:20 multivac pppd[5406]: Exit.

I tried the VPn on two pc's here (one running Ubuntu Karmic, and the 
Other Linux Mint based on Ubuntu Jaunty). On both machine the same issue 
occured, which led me to look at the router as the issue.

As I was grabbing at straws, I changed the MRU from 1400 to 1500 (on the 
modem D-link G604T, running the latest RouterTech firmware), and now my 
VPN stays up, but I have this in my syslog (and it is filling up fast)

Dec 22 08:31:23 multivac pptp[5836]: nm-pptp-service-5831 
log[decaps_gre:pptp_gre.c:414]: buffering packet 87723 (expecting 87672, 
lost or reordered)
Dec 22 08:31:23 multivac pptp[5836]: nm-pptp-service-5831 
log[decaps_gre:pptp_gre.c:414]: buffering packet 87724 (expecting 87672, 
lost or reordered)
Dec 22 08:31:23 multivac pptp[5836]: nm-pptp-service-5831 
log[decaps_gre:pptp_gre.c:414]: buffering packet 87725 (expecting 87672, 
lost or reordered)
Dec 22 08:31:23 multivac pptp[5836]: nm-pptp-service-5831 
log[decaps_gre:pptp_gre.c:414]: buffering packet 87726 (expecting 87672, 
lost or reordered)
Dec 22 08:31:23 multivac pptp[5836]: nm-pptp-service-5831 
log[decaps_gre:pptp_gre.c:414]: buffering packet 87727 (expecting 87676, 
lost or reordered)
Dec 22 08:31:23 multivac pptp[5836]: nm-pptp-service-5831 
log[decaps_gre:pptp_gre.c:414]: buffering packet 87728 (expecting 87676, 
lost or reordered)
Dec 22 08:31:23 multivac pptp[5836]: nm-pptp-service-5831 
log[decaps_gre:pptp_gre.c:414]: buffering packet 87729 (expecting 87676, 
lost or reordered)


Additionally to note is that I have had issues with my broadband for the 
last 2 weeks, with 1 week of near no internet. Bigpond claims the issue 
is now resolved, but since then, this new vpn issue

Any comments or suggestions?
What exactly is the MRU setting doing? (on google I find a lot of MTU 
references, but the router only has a MRU setting)
 From the syslog, I can see that it is not happy, but at least I can 
work now.

TIA
Lucas