[Bug 197511] BPF --> Interactions with Dhclient, Tcpdump, and Network Connections (Ping)

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=197511

            Bug ID: 197511
           Summary: BPF --> Interactions with Dhclient, Tcpdump, and
                    Network Connections (Ping)
           Product: Base System
           Version: 10.1-STABLE
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Only Me
          Priority: ---
         Component: bin
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: garytivey512 at gmail.com

Have noticed on a recent install of FreeBSD 10.1 network firewall (pf) ,by
accident, that if I enable tcpdump on the external interface, I can easily
obtain an IP address via Dhclient on a Comcast cable network. If I close the
Tcpdump program, I can no longer ping external ip's such as google dns, or the
IPV6 endpoint of a 6-4 tunnel. Once I restart the Tcpdump program, all
connectivity is restored. I believe the code in common is the bpf (Berkley
Packet Filter). 

Have observed the same behavior using FreeBSD 9.3 on the same hardware.
Seems rather odd that I need to have tcpdump running all the time on this
firewall. Condition is persistant through reboots. Devices noted in /dev are
bpf, and bpf0. Should there be more bpf devices? I remember a while back the
kernel options allowed a number option... is that still the case?

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