Multicast and hardware checksum

Multicast and hardware checksum

[Baruch Even]

Hello,

I have a machine on which I have an applications that sends multicast 
through eth interface with hardware tx checksum enabled. On the same 
machine I have mrouted running that routes the multicast traffic to a 
set of ppp interfaces. The packets that are received by the client have 
their checksum fixed on some number which is incorrect. If I disable tx 
checksum on the eth device the packets arrive with the proper checksum.

I still haven't followed the code paths to see how to fix this, maybe 
someone knows the relevant code and can find it faster.

Baruch

Re: Multicast and hardware checksum

[Herbert Xu]

Baruch Even <baruch@ev-en.org> wrote:
> 
> I have a machine on which I have an applications that sends multicast 
> through eth interface with hardware tx checksum enabled. On the same 
> machine I have mrouted running that routes the multicast traffic to a 
> set of ppp interfaces. The packets that are received by the client have 
> their checksum fixed on some number which is incorrect. If I disable tx 
> checksum on the eth device the packets arrive with the proper checksum.

Where is the client? On the same machine or behind a PPP link?

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: Multicast and hardware checksum

[Baruch Even]

Herbert Xu wrote:
> Baruch Even <baruch@ev-en.org> wrote:
>> I have a machine on which I have an applications that sends multicast 
>> through eth interface with hardware tx checksum enabled. On the same 
>> machine I have mrouted running that routes the multicast traffic to a 
>> set of ppp interfaces. The packets that are received by the client have 
>> their checksum fixed on some number which is incorrect. If I disable tx 
>> checksum on the eth device the packets arrive with the proper checksum.
> 
> Where is the client? On the same machine or behind a PPP link?

The clients are behind the ppp links.

As far as IGMP and multicast handling everything works, the packets are 
even forwarded over the ppp links but they arrive to the client with a 
bad checksum. I don't have the trace in front of me but I believe it was 
the UDP checksum that failed.

Baruch

Re: Multicast and hardware checksum

[Herbert Xu]

On Fri, Jun 08, 2007 at 02:02:27PM +0300, Baruch Even wrote:
> 
> As far as IGMP and multicast handling everything works, the packets are 
> even forwarded over the ppp links but they arrive to the client with a 
> bad checksum. I don't have the trace in front of me but I believe it was 
> the UDP checksum that failed.

What kind of a ppp device is this?

If you run a tcpdump either side of the ppp link do you see the same
UDP checksum value?

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Re: Multicast and hardware checksum

[Baruch Even]

Herbert Xu wrote:
> On Fri, Jun 08, 2007 at 02:02:27PM +0300, Baruch Even wrote:
>> As far as IGMP and multicast handling everything works, the packets are 
>> even forwarded over the ppp links but they arrive to the client with a 
>> bad checksum. I don't have the trace in front of me but I believe it was 
>> the UDP checksum that failed.
> 
> What kind of a ppp device is this?
> 
> If you run a tcpdump either side of the ppp link do you see the same
> UDP checksum value?

This is a pptp link. I've checked the checksum on the receive side, I 
don't know on the sender side and I'll only be able to try it on Sunday.

Baruch

Re: Multicast and hardware checksum

[Baruch Even]

Baruch Even wrote:
> Herbert Xu wrote:
>> On Fri, Jun 08, 2007 at 02:02:27PM +0300, Baruch Even wrote:
>>> As far as IGMP and multicast handling everything works, the packets 
>>> are even forwarded over the ppp links but they arrive to the client 
>>> with a bad checksum. I don't have the trace in front of me but I 
>>> believe it was the UDP checksum that failed.
>>
>> What kind of a ppp device is this?
>>
>> If you run a tcpdump either side of the ppp link do you see the same
>> UDP checksum value?
> 
> This is a pptp link. I've checked the checksum on the receive side, I 
> don't know on the sender side and I'll only be able to try it on Sunday.

For completeness, the clients are Windows XP clients and the server is a 
  Linux machine. The tunnel is mppe encrypted so I believe that what 
goes out on the client is the same as what got in on the server.

Baruch