[Click] DecIPTTL

[Bart Braem]

On 04 Dec 2008, at 14:11, Nikola Knežević wrote:

> If I have something like this:
>
> FromDevice(ed0) -> Strip(14)
> 		-> DecIPTTL
> 		-> ToDevice(ed1);
>
> system crashes in DecIPTTL. In simple_action, ip_header returns 0x0,
> which gets referenced later.
>
> If I change the configuration to:
> FromDevice(ed0) -> Strip(14)
> 		-> CheckIPHeader
> 		-> DecIPTTL
> 		-> ToDevice(ed1);
>
> then I don't have any problems. Why is this happening? I assume that
> CheckIPHeader sets the proper field of the Packet, but I don't see why
> Strip doesn't do that.



This is Clicks way of working efficiently with packets that have IP  
headers at different positions in the packet.
DecIPTTL expects the IP header annotation to be set and CheckIPHeader  
does that. Strip does not do anything with the IP header annotation.  
Normally you would use a MarkIPHeader element to mark the IP header.

Regards,
Bart Braem
-- 
Bart Braem
PATS research group - IBBT
Dept. of Mathematics and Computer Sciences
University of Antwerp
Campus Middelheim, G3.30
Middelheimlaan 1
B-2020 Antwerpen, Belgium
Phone: +32 (0)3 265.32.91
Fax: +32 (0)3 265.37.77
Web: www.pats.ua.ac.be