Re: obtaining ip address

Thanks for the reply.

>From some digging about, it looks like I should be able to grab the ip from
"pdu->agent_addr" but I'm getting null when trying to print it out and
test.  So that didn't work.

Then it looked like I may be able to get my hands on the sockaddr_in's by
doing (in the callback):

netsnmp_transport *t = (netsnmp_transport *)(session->callback_magic);
//callback_magic was given the transport variable earlier
netsnmp_udp_addr_pair *pp = (netsnmp_udp_addr_pair *)(t->data);

where netsnmp_udp_addr_pair is a struct:
typedef struct netsnmp_udp_addr_pair_s {
     struct sockaddr_in remote_addr;
     struct in_addr local_addr;
} netsnmp_udp_addr_pair;


However, this was returning NULL as well! i.e. t->data was null and
accordingly t->data_length is 0.  Maybe I'm not setting up the
transport/session variables properly or something?  Here's the gist of what
I have:

in main():
netsnmp_session *ss;
netsnmp_transport *transport;
transport = netsnmp_transport_open_server(
"snmptrap", "udp:162");
ss = snmptrapd_add_session(transport);



my snmptrapd_add_session() function:

static netsnmp_session *
snmptrapd_add_session(netsnmp_transport *t)
{
    netsnmp_session sess, *session = &sess, *rc = NULL;

    snmp_sess_init(session);
    session->peername = SNMP_DEFAULT_PEERNAME;  /* Original code had NULL
here */
    session->version = SNMP_DEFAULT_VERSION;
    session->community_len = SNMP_DEFAULT_COMMUNITY_LEN;
    session->retries = SNMP_DEFAULT_RETRIES;
    session->timeout = SNMP_DEFAULT_TIMEOUT;
    session->callback = trap_handler_callback;
    session->callback_magic = (void *) t;  //this is where I give it the
transport variable
    session->authenticator = NULL;
    sess.isAuthoritative = SNMP_SESS_UNKNOWNAUTH;

    rc = snmp_add(session, t, NULL, NULL);
    if (rc == NULL) {
        snmp_sess_perror("exteritytrapd", session);
    }
    return rc;
}

Can anyone see anything that I'm doing wrong?

Thanks,
Tom


On Wed, Feb 16, 2011 at 10:46 AM, Abraham Varricatt <
[email protected]> wrote:

> On Wed, Feb 16, 2011 at 2:29 PM, th exterit <[email protected]> wrote:
>
>> Unfortunately I do not have a choice.  Also, we have a specific network
>> setup where traps are broadcast on the LAN by specific devices with a known
>> OID.  I'm not sure I need worry about those cases you brought up but I could
>> be wrong.  So there is definitely no way to grab the IP from the callback or
>> some such?
>>
>
> A creative (and un-tested) method, is to run multiple agents on different
> ports. If this is just a small LAN network with a handful of agents, you
> could simply have the different agents send the traps to different pots on
> the snmp-manager system. That way, depending on which port the request came
> in, you could isolate which agent sent the message.
>
> A possible limitation of this, is that we have no way of protecting the
> setup against spoofing. Also, I haven't had the need to work with snmp traps
> (yet), so take my advice with a grain of salt.
>
> -Abraham V.
>

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