[P4-dev] INT demo issue - Bad UDP checksum for packets headed to monitor

Rakesh Kumar kumar19 at illinois.edu
Tue May 9 22:13:46 EDT 2017

Hey All,

I was trying to recreate the INT demo on a Ubuntu 14.04 LTS VM and followed
the instructions here:

The network comes up, the hosts are able to connect to each other (i.e.
pings and iperfs between them work), but the web application does not see
any counter updates (i.e. the time series all sit at 0).

So, I tried debugging it. Ultimately, I used tcpdump on each host and
verified that there are UDP packets being sent to the monitor at (IP address for the interface on the native host). These
packets never make it to the destination interface and have a bad UDP
checksum. This explains why the counters are zero, because of course there
are no updates reaching the monitor. But I don't have many ideas about how
to fix this?

Any ideas on what might be causing this? Is it normal/expected behavior due
to some header modifications?

Thanks and Regards,


P.S: Is there a slack where devs hangout if I needed more interactive help
about anything?
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