[Netkit.users] UML kernel versions

Csaba Kiraly kiraly a dit.unitn.it
Mer 14 Nov 2007 00:27:20 CET

Some IPv6 packets were messing up my tcpdump files, so I was looking for 
a way to get rid of these (it could be solved by some tcpdump filters, I 
know, but I wanted to avoid that). While searching with google, I have 
seen that some Debian users were also complaining about performance 
drops due to IPv6 packets.

On  the one hand, a way to disable IPv6 would allow for having "cleaner" 
labs. In theory, modules should work equivalent, even performance should 
be the same.
On the other hand, netkit is for networking experiments, so IPv6 support 
is essential. Kernel code debugging is also easier if it is compiled in 
instead of using modules.

As a consequence, I would say: don't change anything. Our mail is in the 
mail list archives, if someone faces the same problem, he will find it ;)


Massimo Rimondini wrote:
> Thank you Csaba for collecting this information. I can confirm most of 
> these issues have been addressed in the latest release.
> As for the memory amount, you can override the default value by 
> setting a different one either in the ~/.netkit/netkit.conf file or in 
> the environment variable NETKIT_MEMORY. However, we were already 
> thinking of raising the default value to solve some issues with the 
> new kernel. This change should make into the next release.
> You can attempt to disable IPv6 by removing any IPv6 address 
> associated to the network interfaces, but this may not still be 
> enough. I'm not sure switching to a kernel module would be a good 
> choice though: IP routing is something fundamental in Netkit, 
> therefore we chose to enable it by default. Do you have any specific 
> reason to call for the ability to completely disable IPv6?
> Regards,
> Massimo.
> Csaba Kiraly wrote:
>> Dear all,
>> I have been experimenting with many UML kernel version in the last 
>> months, and I wanted to write a mail about the experiences, but I see 
>> now that a new netkit-kernel version (2.3) was coming out.
>> It seems to run on many configurations where I wasn't able to run 
>> netkit, so worth upgrading.
>> With the previous one I had problems:
>> - running it on stock Fedora Core 6
>> - running it after upgrading the filesystem with new glibc
>> and the new one resolves these.
>> I still put here some of the findings briefly.
>> These issues are mostly related to UML, but of course influence 
>> Netkit as well:
>> Netkit refused to run for many reasons. I've seen dependence on:
>> 1, Host kernel version & config
>> 2, Host filesystem
>>    - e.g. existance of /etc/tls
>> 3, Guest kernel version
>> 4, Guest filesystem
>>    - I think the problem was the glibc version. After an upgrade with 
>> apt-get, it wasn't starting with the old (2.6.11 based) kernel
>> 5, Memory for VM
>>    - the default configured in Netkit seems to be too low in many 
>> cases! can it be changed?
>> One more issue that remains (at least for me) in the new kernel is 
>> that the kernel has IPv6 compiled in, which makes it quite difficult 
>> to turn it off. Do you know any good ways to turn it off? Would it be 
>> possible to have IPv6 as a module in the default kernel?
>> Regards
>> Csaba
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