collisions on tun interfaces ...

[YongHyeon PYUN]

On Fri, Apr 29, 2011 at 09:46:34PM +0300, Zeus V Panchenko wrote:
> YongHyeon PYUN (pyunyh at gmail.com) [11.04.29 21:29] wrote:
> > On Fri, Apr 29, 2011 at 12:52:31PM +0300, Zeus V Panchenko wrote:
> > > Hi,
> > > 
> > > may somebody epxplain it for me, what can cause collisions on tun
> > > interfaces created by ppp(8) and openvpn?
> > > 
> > > > uname -a
> > > FreeBSD 8.2-STABLE #0 i386
> > > 
> > > > netstat -i
> > > Name    Mtu Network       Address              Ipkts Ierrs Idrop    Opkts Oerrs  Coll
> > > tun0   1492 <Link#7>                        18940349     0     0 15737760     0 45668
> > > tun0   1492 A.B.C.D A-B-C-D.domain          15623965     -     - 12429351     -     -
> > > tun1   1500 <Link#8>                        12721670     0     0  9957662     0 11161
> > > tun1   1500 E.F.G.H E-F-G-H.vpn     	        6454     -     -   445751     -     -
> > > 
> > > 
> > > rl0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> metric 0 mtu 1500
> > >      options=3808<VLAN_MTU,WOL_UCAST,WOL_MCAST,WOL_MAGIC>
> > >      ether 00:30:4f:67:cf:81
> > >      media: Ethernet autoselect (100baseTX <full-duplex>)
> > >      status: active
> > > tun0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1492
> > >       options=80000<LINKSTATE>
> > >       inet A.B.C.D --> A1.B1.C1.D1 netmask 0xffffffff 
> > >       Opened by PID 3943
> > > tun1: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1500
> > >       options=80000<LINKSTATE>
> > >       inet E.F.G.H --> E1.F1.G1.H1 netmask 0xffffffff 
> > >       Opened by PID 1387
> > > 
> > > tun0 is created by ppp(8)
> > > 
> > > in /etc/ppp.conf is:
> > > default:
> > >  set log Phase Chat LCP IPCP CCP tun command
> > >  set server /var/run/ppp/internet "" 0177
> > >  set device PPPoE:rl0
> > >  set speed sync
> > >  enable lqr echo
> > >  set lqrperiod 30
> > >  set login
> > >  set ctsrts off
> > >  add default HISADDR
> > >  set timeout 0
> > >  set redial 0 0
> > >  set cd 5
> > > 
> > > tun1 is created by OpenVPN with configuration:
> > > client
> > > dev tun1
> > > proto udp
> > > ...
> > > 
> > > so, what can cause the collisions and can i fix them?
> > > 
> > 
> > It seems tun(4) just increments collision counter whenever it
> > can't enqueue packet. Because it's not collision at all I think
> > it's a bug that had been there from day 1. Just nuking updating the
> > counter will address the issue. You still can get the previous
> > collision counter of tun(4) with d option of netstat which shows
> > number of packets dropped due to send queue full.
> 
> thanks, and is there way to influence that?
> 

Sending lots of packets within short interval may overflow
interface's send queue. Try sending UDP packets with netperf and
see what counters are changed during the test with something like
"netstat -ndI tun0 -w 1".