On 11/29/2010 02:16 PM, Iñaki Baz Castillo wrote:
2010/11/29 marius zbihleimarius.zbihlei@1and1.ro:
Kamailio does not use ICMP replies to check if a host is reachable on a UDP sendto(). This means that ICMP port unreachable errors are not handled by K and so the same host is retried on TM retransmits.
AFAIR using raw sockets checking ICMP notifications would be possible (not yet implemented, but possible as I remember from a thread with Andrei).
Possible, but not easily implementable, as ICMP Host unreachable are sent asynchronously from the kernel. Also the current sendto() call does not guarantee delivery on all Unixes (Linux should be fine), connected UDP sockets are to be used instead.
IMHO this would be very useful because if a UDP port is unreachable and there is a ICMP notification about it, the proxy should generate an internal 503 (transport error) rather than a 408 (fr_timer timeout).
Well, this means that we should disable dns_failover (or equivalents) completely and handle ICMP errors in failure_route blocks(just test if the transaction issued a 503). If I recall RFC 3263 , this would mean another server discovery (as the new request generates a new transaction) so again there is the possibility that the broken host is selected. If we use this dns fallback(IMHO this is a nice feature- I personally rely on this) how do we decide to generate a 503 ?
If the host is already a IP address, that it would be ok to send a 503, as no DNS failover is possible.
Ideas?
Marius