Re: MTU size

Hi James,

In addition to my previous mail (sorry I accdiently sent only you instead
in group) I have also some message in my dmesg output as:

ppp: compressor dropped pkt
mppe_compress[31]: osize too small! (have: 1404 need: 1408)
mppe_compress[31]: osize too small! (have: 1404 need: 1408)
mppe_compress[19]: osize too small! (have: 1404 need: 1408)
mppe_compress[19]: osize too small! (have: 1404 need: 1408)
mppe_compress[19]: osize too small! (have: 1404 need: 1408)
mppe_compress[19]: osize too small! (have: 1404 need: 1408)
mppe_compress[19]: osize too small! (have: 1404 need: 1408)
mppe_compress[19]: osize too small! (have: 1404 need: 1408)
mppe_compress[19]: osize too small! (have: 1404 need: 1408)
mppe_compress[46]: osize too small! (have: 1404 need: 1408)
__ratelimit: 9 callbacks suppressed
ppp: compressor dropped pkt
mppe_compress[33]: osize too small! (have: 1404 need: 1408)
ppp: compressor dropped pkt
mppe_compress[33]: osize too small! (have: 1404 need: 1408)
ppp: compressor dropped pkt
mppe_compress[33]: osize too small! (have: 1404 need: 1408)
ppp: compressor dropped pkt
mppe_compress[33]: osize too small! (have: 1404 need: 1408



Thanks James,

these is only few users who are having issue, I will monitor their vpn
connection and change the MTU size if needed. But where can I make change
the MTU in VPN server ? is it in /etc/ppp/ip-up file ?

And, I see constantly following in the ppp.log files, could you please give
me some hint or direction on resolving these issue ?

Nov 17 15:59:58 myvpn pptpd[32735]: MGR: dropped small initial connection
Nov 19 17:58:50 myvpn pptpd[32735]: MGR: dropped slow initial connection
Nov 19 19:35:16 myvpn pptpd[32735]: MGR: dropped slow initial connection
Nov 20 10:57:20 myvpn pptpd[32735]: MGR: dropped small initial connection
Nov 20 20:45:19 myvpn pptpd[32735]: MGR: dropped small initial connection


Nov 17 08:32:17 myvpn pppd[27865]: Protocol-Reject for unsupported protocol
0xb5
Nov 17 08:32:17 myvpn pppd[27865]: rcvd [LCP ProtRej id=0x73 d2 f5 79 0b 84
9c a4 ed 92 9c eb 76 88 e1 ce 0c 93 22 aa d3 03 ec 86 d0 91 3c d2 36 73 ea
37 7b ...]
Nov 17 08:32:17 myvpn pppd[27865]: Protocol-Reject for unsupported protocol
0xd2f5



Nov 21 11:05:37 myvpn pppd[15722]: RADATTR plugin wrote 8 line(s) to file
/var/run/radattr.ppp4.
Nov 21 11:05:37 myvpn pppd[15722]: sent [CHAP Success id=0x78
"S=28725A4220EC643C53787A58E22D4023A0B0C796"]
Nov 21 11:05:37 myvpn pppd[15722]: sent [CCP ConfReq id=0x1 <mppe +H -M +S
-L -D -C>]
Nov 21 11:05:37 myvpn pppd[15722]: rcvd [CCP ConfReq id=0x1 <mppe -H +M +S
+L -D -C>]
Nov 21 11:05:37 myvpn pppd[15722]: Refusing MPPE stateful mode offered by
peer
Nov 21 11:05:37 myvpn pppd[15722]: MPPE required but peer negotiation failed

Nov 19 16:13:33 myvpn pptpd[7669]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:13:42 myvpn pptpd[7679]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:13:52 myvpn pptpd[7689]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:14:02 myvpn pptpd[7710]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:14:11 myvpn pptpd[7734]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:14:24 myvpn pptpd[7744]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:14:34 myvpn pptpd[7754]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:14:47 myvpn pptpd[7765]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)
Nov 19 16:14:58 myvpn pptpd[7775]: CTRL: PTY read or GRE write failed
(pty,gre)=(6,7)





On Tue, Nov 19, 2013 at 8:30 PM, James Cameron <[email protected]> wrote:

> Summary:
>
> The MTU should be left at 1500, or lowered to whatever works.
> You have to test with many many IP addresses to find the right MTU.
>
> Detail:
>
> When IP packets are sent over PPP, they grow slightly.  When the
> packets are then sent over GRE, they grow some more.  This growth
> makes them too big to fit in the usual 1500 limit.
>
> Normally, when everything is working correctly, the packets are split
> into two parts and sent one after the other, and then reassembled at
> the other side.
>
> Sometimes, the need to split the packets cannot be determined at the
> server or the client, because the need is recognised by a node in the
> network between the server and the client.  The need is transmitted in
> a separate message, called an ICMP Fragmentation Needed.  This message
> comes from a third-party to either the server or the client.
>
> Further, sometimes this message is blocked, by accident, by policy, by
> security.  When that happens, the server or the client don't know that
> their original packet didn't get through, and so the connection
> freezes.
>
> If lowering the MTU fixes the symptom, then it is a reasonable guess
> that the above description is the problem.
>
> You can find more on this at
> http://en.wikipedia.org/wiki/Path_MTU_Discovery
>
> On Tue, Nov 19, 2013 at 12:31:15PM +0000, Khapare Joshi wrote:
> > Just curios what MTU size ppp server should be configured ?
> >
> > I see some of those ppp client has
> >
> >  UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1396  Metric:1
> >
> > UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1496  Metric:1
> >
> > Why this is ? should not be 1500 for every client that connect to vpn ?
> >
> > So the problem is some of my users can connect to my VPN server but they
> could
> > not get anything such as website outside my company as an example.
>
> --
> James Cameron
> http://quozl.linux.org.au/
>

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