Hi,
you are probably facing a routing issue, and you need to solve it by
using different network namespaces (netns).
In your current setup, you probably have routing for those DNS packets
to go through the sgsnemu iface, and once the ggsn puts them again in
the network stack after going through GTP, the kernel probably ends up
dropping the packet because it finds out some sort of loop.
In order to solve it, the easiest is to run sgsnemu under a different
netns, and set default routing inside that netns to the tun iface
created by sgsnemu. AFAIR, the netns can take care of creating the netns
and configuring it for you, check it's man page ("--defaultroute",
"--netns").
Hope this is useful to you,
Pau
--
- Pau Espin Pedrol <pespin(a)sysmocom.de>
http://www.sysmocom.de/
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