Re: Multicast and UDP checksums

[christos%astron.com@localhost (Christos Zoulas)]

In article <50315ED7.6030203%netbsd.org@localhost>,
Frank Kardel  <kardel%netbsd.org@localhost> wrote:
>Hi,
>
>while debugging ntp multicast issues I found a strange behaviour on 6.99.5.
>
>ntpd in machine A (amd64, wm interface) sends multicast packets to 
>224.0.1.1.
>
>tcpdump on machine B (amd64, wm interface) sees both packets types
>fine (no complaints about the checksum).
>
>ntpd on machine B never sees the multicast packets, because they get 
>dropped due to 'bad checksum' in the udp4_realinput() path.
>
>ntpd on machine B sees the plain broadcast packets, because the checksum
>is fine.
>
>Any ideas why the ntp multicast packets get dropped, but tcpdump
>finds nothing wrong about them ?

Do you have hardware checksumming on, on either side?

christos