[OpenVPN home] [Date Prev] [Date Index] [Date Next]
[OpenVPN mailing lists] [Thread Prev] [Thread Index] [Thread Next]
Google
 
Web openvpn.net

Re: [Openvpn-users] Tunnel MTU


  • Subject: Re: [Openvpn-users] Tunnel MTU
  • From: "James Yonan" <jim@xxxxxxxxx>
  • Date: Thu, 12 Jun 2003 11:39:51 -0000

Carsten,

Yes, OpenVPN passes potentially large packets (>1500) to sendto and relies on
the kernel to fragment.

OpenVPN also has a new feature (in the current development version 1.4.1.4)
that does fragmentation internally.  Look for --mtu-dynamic in the archives
for more info.

James

Carsten Burstedde <bursted@xxxxxxxxxxxxxxx> said:

> Thanks James.
> 
> These was the MTU information I was missing (and on second reading, I 
> found it in the archives, too).  It seems to work.  Does linux fragment 
> automatically when a 1500 byte packet comes in on the ethernet and 
> either goes out regularly over pppoe (mtu 1492) or through the tunnel 
> (br0=eth0,tap0 -> 1500 + extra_mtu + openvpn overhead -> udp (1492))? 
> Does openvpn just pass <= 1608 byte datagrams to send/sendto(2)?
> 
> I might write a short doc on Debian and my star-like setup once I sorted 
> everything out and a serious windows-lan-game-test has passed, trying 
> not to duplicate Chuck's infos.
> 
> Carsten
> 
> > Check the archives for more posts about ethernet bridging.
> > 
> > Also, make sure to use --tun-mtu 1500 --tun-mtu-extra 64 when you bridge a tap
> > dev with a physical ethernet device.  Don't use 1300.
> 
> >>I am planning to bridge two or more LANs behind dial-up linux routers 
> >>together, in a star-like setup.
> >>
> >>         my router          server            another router
> >>  LAN -- eth0 tap0 ------- tap0 tap1 ---------- tap0 eth0 -- LAN
> >>           \br0/             \br0/                \br0/
> >>                           tap2 etc.
> >>                   etc. -----/
> >>
> >>The tunnel UDP connections go over PPPoE(th1) links (DSL), the server is 
> >>located somewhere on the internet (high bandwidth).
> >>
> >>Do I have to set the mtu to 1300 for each and every participating 
> >>interface, i.e. eth0, br0 and tap0 on the routers and tapx and br0 on 
> >>the server? And also on all machines sitting in the various LANs? That 
> >>would be a lot of administrative effort.
> >>
> >>Currently, I set up the bridges with eth0 and mtu at boot time and execute
> >>   ifconfig $1 mtu $2 up
> >>   brctl addif br0 $1
> >>in the up-scripts.
> 
> -- 
> Carsten Burstedde <bursted@xxxxxxxxxxxxxxx>
> GPG fingerprint
>     3B2B BA5E A3A1 0A5F 4AD8
>     D515 4429 5406 061B A3F9
> 
> 
> 
> -------------------------------------------------------
> This SF.NET email is sponsored by: eBay
> Great deals on office technology -- on eBay now! Click here:
> http://adfarm.mediaplex.com/ad/ck/711-11697-6916-5
> _______________________________________________
> Openvpn-users mailing list
> Openvpn-users@xxxxxxxxxxxxxxxxxxxxx
> https://lists.sourceforge.net/lists/listinfo/openvpn-users
> 



-- 




____________________________________________
Openvpn-users mailing list
Openvpn-users@xxxxxxxxxxxxxxxxxxxxx
https://lists.sourceforge.net/lists/listinfo/openvpn-users