Re: SNMPD v5.8 Error opening specified endpoint

On Sat, Aug 25, 2018 at 3:45 PM Martin Frlin <[email protected]> wrote:

> If you specify trapsink line in form localhost:<port> it does not bind a
> socket because it does not set a source in the piece of code I have linked.
>

I was suggesting adding "-s 127.0.0.1:<some high level port>" to your
trapsink line, like

trapsink -s 127.0.0.1:62134 localhost public
and
trapsink -s 127.0.0.1:0 localhost public

Regarding why it binds to port 161 I don't understand your comment. I know
> that destination port will be 162 because that is where the snmptrapd
> listens (by default).
>

The code that's being used to turn "localhost" into a transport spec thinks
it's being used for an SNMP listener, not a clientaddr, so it defaults to
port 161.  This looks like it's a bug that was added in 5.8, and partially
worked around with the new "clientaddrUsesPort" configuration that you
found but as you found that's also buggy.


> If someone can explain the reasoning why is binding happening if trapsink
> is on localhost and not if it is on remote and why it always binds on port
> 161 thus creating a problem I could make a patch that resolves this issue.
>

I don't quite know why this behavior is desirable.  From the comment, I
*think* the intent to address the problem that a socket that is bound to a
port will receive packets destined to that port, so if you bind to
0.0.0.0:62134 and someone sends you a packet to port 62134 that socket will
receive it.  This isn't much of a problem since snmpd never reads from this
port.  The intention is to bind to localhost:0, which will cause the kernel
to pick a port, but due to the bug I mentioned above it tries to use
localhost:161.

  Bill

V V pet., 24. avg. 2018 ob 19:57 je oseba Bill Fenner <[email protected]>
> napisala:
>
>> On Thu, Aug 23, 2018 at 9:24 AM Martin Frlin <[email protected]>
>> wrote:
>>
>>> Ok, additional information.
>>> Compare this line in v5.8:
>>> https://sourceforge.net/p/net-snmp/code/ci/master/tree/agent/agent_trap.c#l358
>>> with this line
>>> https://sourceforge.net/p/net-snmp/code/ci/v5.7.3/tree/agent/agent_trap.c#l251
>>>
>>> You will see that v5.7 does not set a source. And because it does not
>>> set a source it does not bind.
>>>
>>> But maybe we want to bind? (Source says we want to reduce open ports but
>>> I don't understand this)
>>>
>>> Ok, but why bind on port 161? If understand correctly we want to SEND
>>> traps. So we should bind localhost:<random high level port> ->
>>> localhost:162 (address of our snmptrapd), but this does not happen.
>>> Instead we get (note that netsnmp prints to->from):
>>> netsnmp_udpbase: binding socket: 9 to UDP: [0.0.0.0]:0->[127.0.0.1]:161
>>> netsnmp_udpbase: socket 9 bound to UDP: [127.0.0.1]:162->[127.0.0.1]:161
>>>
>>> So why is socket bound on port 161 instead of some random high level
>>> port? I didn't find where in code port 161 is set.
>>>
>>
>> It comes from the code that parses transport specifications.  But it's
>> assuming that it's parsing a destination, not a source.  Even if you told
>> that code that you were doing the lookup in the context of a trap, it would
>> use 162.
>>
>> So I think the solution is that either port is unbound or random high
>>> level port is chosen for binding.
>>>
>>> I've also tried to set
>>> clientaddr 127.0.0.1:<some high level port>
>>> clientaddrUsesPort yes
>>> because documentation says this will be used for clients but it also
>>> does not work.
>>>
>>
>> Can you try adding "-s 127.0.0.1:<some high level port>" to your
>> trapsink line instead?  You can also try ":0".
>>
>> I found a few bugs in the clientaddr changes before 5.8 went out, but I
>> don't use trapsink so didn't notice this one.  There are a bunch of hacks
>> in the clientaddr support that would clearly have been better to push into
>> the transport parsing instead.
>>
>>   Bill
>>
>>
>>> V V čet., 23. avg. 2018 ob 11:47 je oseba Martin Frlin <
>>> [email protected]> napisala:
>>>
>>>> If you have line:
>>>> trapsink     localhost public
>>>> in your config v5.8 fails to start. Meanwhile v5.3 starts with no
>>>> problems.
>>>>
>>>> Am I missing something or is this a bug?.
>>>>
>>>> This output was generated using exactly the same config
>>>> v5.8
>>>> # snmpd -Dnetsnmp_udpbase -Lo -f
>>>> registered debug token netsnmp_udpbase, 1
>>>> Log handling defined - disabling stderr
>>>> netsnmp_udpbase: open remote UDP: [127.0.0.1]:162->[0.0.0.0]:0
>>>> netsnmp_udpbase: binding socket: 9 to UDP: [0.0.0.0]:0->[127.0.0.1]:161
>>>> netsnmp_udpbase: socket 9 bound to UDP: [127.0.0.1]:162->[127.0.0.1]:161
>>>> Turning on AgentX master support.
>>>> netsnmp_udpbase: open local UDP: [127.0.0.1]:161->[0.0.0.0]:0
>>>> netsnmp_udpbase: set IP_PKTINFO
>>>> netsnmp_udpbase: binding socket: 8 to UDP: [0.0.0.0]:0->[127.0.0.1]:161
>>>> netsnmp_udpbase: failed to bind for clientaddr: 98 Address already in
>>>> use
>>>> Error opening specified endpoint "udp:127.0.0.1:161"
>>>> Server Exiting with code 1
>>>>
>>>>
>>>> v5.3
>>>> # snmpd -Dnetsnmp_udpbase -Lo -f
>>>> registered debug token netsnmp_udpbase, 1
>>>> Log handling defined - disabling stderr
>>>> netsnmp_udpbase: open remote UDP: [127.0.0.1]:162->[0.0.0.0]:0
>>>> netsnmp_udpbase: client open UDP: [127.0.0.1]:162->[0.0.0.0]:0
>>>> Turning on AgentX master support.
>>>> netsnmp_udpbase: open local UDP: [127.0.0.1]:161->[0.0.0.0]:0
>>>> netsnmp_udpbase: set IP_PKTINFO
>>>>
>>>
>>> ------------------------------------------------------------------------------
>>> Check out the vibrant tech community on one of the world's most
>>> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
>>> _______________________________________________
>>> Net-snmp-users mailing list
>>> [email protected]
>>> Please see the following page to unsubscribe or change other options:
>>> https://lists.sourceforge.net/lists/listinfo/net-snmp-users
>>>
>>

------------------------------------------------------------------------------
Check out the vibrant tech community on one of the world's most
engaging tech sites, Slashdot.org! http://sdm.link/slashdot

_______________________________________________
Net-snmp-users mailing list
[email protected]
Please see the following page to unsubscribe or change other options:
https://lists.sourceforge.net/lists/listinfo/net-snmp-users