traceroute using different interfaces for inbound and outbound traffic

[rafajot]

Hi, I'm wondering if it would be possible to issue the (as)traceroute in a way that one interface is used for outgoing traffic and other interface (for example span port) would be used to listen for responses? I guess a bridge interface possibly could do the job but maybe there is a simpler solution to that problem with netsniff-ng.

[tklauser]

At the moment this is not possible without configuring a bridge interface (or possibly some other virtual interface method). Do you have a specific use case in mind for this feature which a Linux bridge can't deal with and strictly require astraceroute to support this?

[rafajot]

I need it because from time to time I have to forge IP for someone who can't/don't want to do the traceroute on the box I can't access in my organization.
I tried to achieve that goal using scapy but it didn't work for me. So at the moment I just create alias interface and use tcpdump on a span port on another interface.
Would bridge interface (with any tracreoute implementation) do the job? - Probably yes, I just need to test it in order not to break the production environment. Anyway obviously it would be very nice to have such functionality in traceroute ;-) (even though it would require root access)

[tklauser]

Ok, thanks for the info. I haven't tried with a bridge, but would suspect it should work.