It's not an old kernel, or the card, or tcpdump....it's the way the
socket option is used on linux. I checked the linux kernel source.
When SO_NO_CHECK is set it uses:
0=normal default, generate UDP checksum.
1=do not send checksums, set it to 0
This is a send only option. It does not change the way asterisk recives
UDP packets. The asterisk default is to NOT send UDP checksums with RTP....
I guess I should have looked into it a little more....so I'll say it's
not a bug, it's a choice. With no checksum there is a chance of 2 bytes
less in a compressed packet (cRTP) and the kernel (or hardware) does not
have to compute the checksum. So this whole thing is a non-issue.
FYI: Code from the Linux kernel.....if no check sum than it skips it and
just sends the packet.
if (sk->sk_no_check == UDP_CSUM_NOXMIT) {
skb->ip_summed = CHECKSUM_NONE;
goto send;
}
>
>Michael Loftis wrote:
>
>> This is a possibility, there are a decent number of hardware supported
>> offload engines built into ethernet cards nowadays....though I don't
>> know how many support UDP...but if yours does then you could end up
>> without UDP checksums until it actually goes out on the wire.
>
>Very true... nearly every decent Ethernet card nowadays does IP
>checksums on its own, many of them probably do UDP checksums as well.
Andrew
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