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From: Matt Miller <matt@matthewjmiller.net>
Date: Wed, 13 Mar 2013 21:11:49 -0400
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Subject: Re: ip_output() Error Handling in tcp_output()
To: Chuck Swiger <cswiger@mac.com>
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On Wed, Mar 13, 2013 at 3:35 PM, Chuck Swiger <cswiger@mac.com> wrote:
> Hi--
>
> On Mar 13, 2013, at 8:21 AM, Matt Miller wrote:
>> If we have a connection that has received a SYN and ip_output()
>> returns, say, EHOSTUNREACH, is there anything that guarantees the
>> connection would always eventually be dropped if the condition
>> persists?
>
> If the local TCP stack is unable to reply with a SYN-ACK, then it hasn't established a connection yet because it cannot proceed through the 3WHS to ESTAB.  It will stay in LISTEN state.
>

Sorry, I should have been more specific: say the connection has
already progressed to at least ESTABLISHED or beyond when the
ip_output() error occurs.  So, we'll hit the TCPS_HAVERCVDSYN if block
below:

                case EHOSTDOWN:
                case EHOSTUNREACH:
                case ENETDOWN:
                case ENETUNREACH:
                        if (TCPS_HAVERCVDSYN(tp->t_state)) {
                                tp->t_softerror = error;
                                return (0);
                        }

Thanks,

Matt

> Regards,
> --
> -Chuck
>