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Masquerading stopped working when gone from kernel 2.4 to 22

Posted on 2001-09-13
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Hi,

I tried to move to the 2.4 kernel with great success apart from my external ISDN modem will not respond.  Followed all instructions and even asked another question on ee.  I've now given up and moved back to 2.2.12-20.  The modem respods properly but my ip masquerading seems to have gone a bit funny....

I can ping the linux server and ping through it to sites on the web but I can't use any other protocol. DNS, telnet, http etc all don't want to connect even direct to the server it's self, which is running named, a web server (orion) and obviously inetd for telnet et al.

I have upgraded to RH7.1 but downgraded back to the old 2.2 kernel since I can't get the modem to respond, which is when the problems started.
ipchains 1.3.10-7
iproute 2.2.4-10

Any ideas would be fantastic.  Thanks for your time,
Tim.
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Question by:tims
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by:ahoffmann
ID: 6485623
do you have a default route to the interface of your modem or ISDN?
check with:
   ifconfig -a; netstat -rn
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jlevie earned 800 total points
ID: 6485877
I'm not at all sure that you could sucessfully run a 2.2.x kernel on a system that had been upgraded to RedHat 7.1. More than just the kernel would have to be changed to go back to 2.2.x functionality. I suspect that you'll have to go back to the version of ipchains from the 7.0 distribution. And there may be other packages that you'll have to downgrade to get everything to work. It would seem safest to me to simply back up your data, and re-install 7.0 from scratch. At least that way you'd have a known configuration.

If the original system was in a sane state and the upgrade completed sucessfully. There's little reason for an external ISDN modem not to work. They look like standard Hayes compatible modems and respond to the 'AT' command set. The only cases I've seen where ordinary devices like COM ports. fairly standard NIC's, etc., failed to work after an upgrade to 7.1 have all involved a resource conflict. And that's usually because 7.1 will load the USB driver if it finds a USB controller on the system. The 2.2.x kernel didn't support USB and since it didn't load a driver there would be no conflict. Also support for PnP devices changed in 2.4 and that can cause problems on some configurations. Resource conflicts aren't difficult to detect. One can look at the output of 'dmesg | grep -i irq', the contents of /proc/pci & /proc/interrupts, and make a list of IRQ assignments. Any resource conflicts, two devices using the same IRQ, will become obvious. FWIW I have seen a couple of cases where an ungrade to a 2.4.x kernel broke some devices that weren't involved in a resource conflict. In one case PnP mode was enabled in the system BIOS (Linux doesn't like that) and in another the system BIOS was a old version. The obvious remedies were applied and all is well with those boxes now.

Now, if the system wasn't in a sane state when the upgrade was done things can get screwy. By that I mean a system that has had various RedHat packages replaced by non-RedHat rpms or packages relaced by locally compiled source distributions. If the replaced items are system type packages the upgrade process may not have completely upgraded the system as the corresponding RedHat wasn't found during the upgrade.  
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Author Comment

by:tims
ID: 6494240
It was the irq problem.  An old isa modem was irq5 - the same as the serial port.

Thanks for the detailed answer, it had to be in there somewhere!
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