DaemonForums  

Go Back   DaemonForums > NetBSD > NetBSD General

NetBSD General Other questions regarding NetBSD which do not fit in any of the categories below.

 
 
Thread Tools Display Modes
Prev Previous Post   Next Post Next
  #1   (View Single Post)  
Old 9th March 2009
IdOp's Avatar
IdOp IdOp is offline
Too dumb for a smartphone
 
Join Date: May 2008
Location: twisting on the daemon's fork(2)
Posts: 1,027
Question Ethernet UP clobbers PPP

I've been having a bizarre problem with NetBSD i386 4.0.1 -release (and before that on 4.0 -release). After a bunch of trial and error, I found a solution to the problem. That's great insofar as "it works" now, but I still don't understand why the problem was happening, hence this post.

For now I just want to give a concise description of the setup, problem and solution, so that people can quickly see where it's going. Of course, I'd be glad to post more details as needed.

The setup is a box with a single modem and single network card (a Via Rhine II, interface vr0). The modem dials up to "the Internet" and vr0 connects to the local LAN. There is no NAT or IP forwarding going on; things are fairly much out of the box. Connections to the LAN work fine.

This was the problem: When connected with pppd to the Internet (interface ppp0), this connection does not work right when vr0 is UP. If I put vr0 DOWN, the ppp connection soon starts to work right. (This is from the box, not the LAN.) What do I mean by not right? Well, it seems DNS is working, but loading almost any web page will hang up after DNS and the request is sent -- unless maybe it is a very small web page.

Note, the same thing works just fine with Linux and OpenBSD, so it doesn't seem to be a hardware problem.

BTW the routing looks ok:
Code:
# route show | head
default            Remote-IP          UG
10.0.1.0/24        link#1             U
loopback           127.0.0.1          UGR
localhost          127.0.0.1          UH
Remote-Host        Local-IP           UH
(Hostname and IP addresses cloaked by me.)

The problem manifests as errors on the ppp0 interface:
Code:
# ifconfig -v ppp0
ppp0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1450
        input: 44 packets, 16992 bytes, 10 errors
        output: 50 packets, 3523 bytes
        inet Local-IP -> Remote-IP netmask 0xff000000
        inet6 fe80::250:baff:fe26:b0a3%ppp0 ->  prefixlen 64 scopeid 0x3
After a lot of frustration, the solution I found was: In the PPP setup, I'd been using MRU of 1280. Due to some of the symptoms above, I tried increasing it to the max of 1524, and the problem went away! After some experiments it seems that an MRU >= 1500 works, and anything less probably gives the problem. As an aside, the MTU of vr0 is of course 1500.

So the questions are, why on earth would the UP/DOWN state of the ethernet link affect the PPP connection, and only for too small MRU's? Could this cause other problems? Is there a better solution?

I'd be grateful for any insight anyone might have on this. Thank you.

Last edited by IdOp; 9th March 2009 at 02:29 AM.
Reply With Quote
 

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Broadcom BCM5906M 10/100 Ethernet Driver? revzalot Solaris 0 15th June 2009 05:47 PM
My D-Link DFE530TX ethernet adapter isnt found. Help! Quaxo OpenBSD Installation and Upgrading 15 10th February 2009 12:23 AM
broadcom ethernet jaideep_jdof NetBSD General 0 16th November 2008 05:33 PM
Activating/deactivating Ethernet card rex FreeBSD General 9 4th September 2008 07:00 PM
Installing software without Ethernet Card welkin FreeBSD Ports and Packages 2 27th July 2008 12:12 AM


All times are GMT. The time now is 11:44 AM.


Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Content copyright © 2007-2010, the authors
Daemon image copyright ©1988, Marshall Kirk McKusick