[Bro] Dropped packets in PF_RING install

[Nicholas SIow]

Hi Bro,


We have an install of bro running on a single machine with PF_RING load balancing.

Previously we were seeing a huge amount of dropped traffic — in the realm of ~90% average packet loss per hour. The history column in our `conn.log` was trash as expected, with only one or two letters per connection.

After some tweaking (adding memory & upping # of bro processes & changing PF_RING buffer size), the logs look much better and the packet loss is drastically reduced, to about 0.5%-1% loss per hour. However, both `broctl netstats` and `cat /proc/net/pf_ring/*eth0*` report some packet loss still.

Is the sub-1% packet loss we’re seeing expected/optimal or are there additional tweaks that we could add to push this down to 0%?

### some notes ###

> both `tcpdump -nn -s0 -vv -i eth0 -w /dev/null` and the pfcount.c utility from pf_ring report 0% packet loss. It’s not until we start using bro that we start seeing dropped packets.

> we’re currently using 16 bro processes pinned to 16 of 32 total processors

> PF_RING buffer size is currently 65536

> packet loss does seem to go down during low-traffic hours but during the day when traffic is 2.5-3 gbps is when the dropped packet count peaks (while still being a small percentage of the overall traffic)


Let me know if you guys have any thoughts on this, thanks!


- - -
Nicholas Siow
Washington University in St. Louis :: Information Security 
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