[streaming] SAP problem

[Marshall Eubanks]

On Oct 16, 2007, at 4:30 AM, Tomasz Szewczyk wrote:

> Rémi Denis-Courmont pisze:
>> Le Monday 15 October 2007 16:26:16 Tomasz Szewczyk, vous avez écrit :
>>
>>> I just tried to start multicast stream announced by SAP/SDP with VLC
>>> 0.8.6c. The problem is that SAP message contains (almost) random
>>> Originating Source IP address. I captured the SAP packet (with  
>>> wireshark).
>>>
>>
>> Which address do you mean? the originating address (o=) is purely  
>> informational, so while it should not be random, it should not  
>> matter either.
>>
>> I recall some bug whereby the source filter specification  
>> contained the destination multicast address instead of the source  
>> - I thought that was fixed in 0.8.6c, but you can try the  
>> development tree if not.
>>
>> Could you paste the faulty SDP please?
>>
>>
> Here is the example (output from Cisco)
>
> Session Name: psnc-test
>  Description:
>  Group: 233.35.152.11, ttl: 0, Contiguous allocation: 0

Note the ttl. A ttl of zero will not propagate.

>  Uptime: 00:00:25, Last Heard: 00:00:00
>  Announcement source: 120.1.62.0, destination: 224.2.127.254
>  Created by: - 339647032040 898 IN IP4 150.254.210.89
>  Phone number:
>  Email:
>  URL:
>  Media: video 1234 RTP/AVP 33
>


Here is what is in the file, which agrees with the above, except for  
the source address

o=- 339888892459 1797 IN IP4 150.254.210.89
s=psnc-test
c=IN IP4 233.35.152.11
t=0 0
a=tool:vlc 0.8.6c
a=recvonly
a=type:broadcast
m=video 1234 RTP/AVP 33


>
> I attached the SAP packet captured with wireshark. I think SDP  
> contains correct information but take a look at SAP Originating  
> Source value. It differs form IP packet source and "o=" value in  
> SDP message. Moreover, the SAP originating source field changes  
> everytime when the streaming is stopped and started again (Stop/ 
> Play buttons).
>
> I think this could cause that some routers can discard the SAP  
> message with wrong address. For instance the SAP is "vissible" on  
> first-hop cisco router, but it doesn't appear on neighboring  
> juniper router.

A ttl of zero will not go anywhere.

Change the ttl, and report back. That's a SAP problem, not an SDP  
problem.

Regards
Marshall


>
> Tomek
>
> <capture.zip>
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