[Xorp-hackers] A problem with the Router Alert option

[Ben Greear]

On 09/11/2012 10:29 AM, Nenad Vukmirovic wrote:
> I have a question about raw IPv4 packet input/output.
>
> I am working on a new XORP module (protocol) which uses raw IPv4 IO and
> relies on the Router Alert option to work properly. I have managed to send
> packets with that option (flag) set to ON successfully so far. I have also
> received packets that have the destination IP address of my router (in the
> IP header).
>
> However, it seems I cannot receive packets (with the Router Alert flag
> turned on) whose destination IP address doesn't match any address on my
> router.
>
> I have checked that those packets arrive at my router and that my router
> forwards them to their final destination, but those packets don't get
> inspected by my protocol (running on the router).
>
> Does anyone know if FEA is capable of letting such packets into the
> protocol to be inspected automatically? If it is, what part of my code
> should I change to make it work?

Not sure, but the 'io_ip_socket.cc' file is likely the place to
start looking.

You might have to create a socket that listens for all packets
and then uses a pcap-filter to deliver only the RA packets to
user-space?

Thanks,
Ben

>
> Yours faithfully,
> Nenad Vukmirovic
>
>
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-- 
Ben Greear <greearb at candelatech.com>
Candela Technologies Inc  http://www.candelatech.com