Hi. Here is a script snippet which detects the interface containing the default route. I would guess that this is usually the interface the user will want to monitor.
DEFAULTDEV="`ip route | grep default | \
sed -e 's/.*dev //;s/ *src.*//' | \
sort -u`"
Perhaps this helps further improving on this issue. The above requires
the iproute package to be installed. An alternative using net-tools
would look like this:
DEFAULTDEV="`route -n | grep -E '0.0.0.0 *[0-9.]* *0.0.0.0' | \
awk '{print $8;}'`"
Unfortunately, there are setups which carry multiple default routes (and
those setups can work). In these setups, the iproute version above
returns multiple device entries seperated by spaces. The net-tools
version might fail in those setups (multiple default routes can only be
set with the iproute 'ip' tool), I don't know.
However, the iproute version should return usable default values in most
setups, as long as a single default route exists. If there is no default
route, it will simply return an empty string, which could lead to
further tests.
Regards,
Sven
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