Pysnmp openServerMode with IPv6

Question

I try to start a SNMP Agent with pysnmp. for IPv4 and IPv6 bind, it works pretty fine with localhost ('127.0.0.1' and '::1')

but when I try to use other IPv6 IP which I fetched from interface, it failed due to

[vagrant@test SOURCES]$ sudo python snmp_agent.py enp0s8
Traceback (most recent call last):
  File "snmp_agent.py", line 172, in <module>
    master_agent_startup(ifname=sys.argv[1])
  File "snmp_agent.py", line 101, in master_agent_startup
    (get_ipv6_address(interface_name), SNMP_AGENT_PORT))
  File "/usr/lib/python2.7/site-packages/pysnmp/carrier/asyncore/dgram/base.py", line 50, in openServerMode
    raise error.CarrierError('bind() for %s failed: %s' % (iface, sys.exc_info()[1],))
pysnmp.carrier.error.CarrierError: bind() for ('fe80::a00:27ff:fe9e:9c16', 8001) failed: [Errno 22] Invalid argument

This is the output from the interface 'enp0s8':

[vagrant@test SOURCES]$ ifconfig enp0s8
enp0s8: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 172.20.20.26  netmask 255.255.255.0  broadcast 172.20.20.255
        inet6 fe80::a00:27ff:fe9e:9c16  prefixlen 64  scopeid 0x20<link>
        ether 08:00:27:9e:9c:16  txqueuelen 1000  (Ethernet)
        RX packets 874053  bytes 115842841 (110.4 MiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 862314  bytes 114652475 (109.3 MiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

This is the code piece I used for IPv6 bind:

def get_ipv6_address(ifname):
    return netifaces.ifaddresses(ifname)[netifaces.AF_INET6][0]['addr'].split('%')[0]

config.addSocketTransport(snmpEngine, udp.domainName,
                          udp.UdpTransport().openServerMode(
                              (get_ipv4_address(interface_name), SNMP_AGENT_PORT))
                          )
config.addSocketTransport(snmpEngine, udp6.domainName,
                          udp6.Udp6SocketTransport().openServerMode(
                              (get_ipv6_address(interface_name), SNMP_AGENT_PORT))
                          )

From pysnmp sample, it seems the parameter inside "openServerMode()" is just a tuple of IP and port. And from output error I suppose there is no error for given IP and port. so why it failed due to Invalid argument? Could you @Ilya Etingof or some other pysnmp expert help me with it?

Thanks.

UPDATE: I try to bind it with given suggestion, but is still doesn't work. the bind command was run from a new installed CentOS. but it still failed: [root@test ~]# ifconfig

eth1: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.10.20.4  netmask 255.255.255.0  broadcast 10.10.20.255
        inet6 fe80::f816:3eff:fee1:5475  prefixlen 64  scopeid 0x20<link>
        ether fa:16:3e:e1:54:75  txqueuelen 1000  (Ethernet)
        RX packets 12242  bytes 962552 (939.9 KiB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 12196  bytes 957826 (935.3 KiB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

[root@test ~]# python
Python 2.7.5 (default, Oct 11 2015, 17:47:16)
[GCC 4.8.3 20140911 (Red Hat 4.8.3-9)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import socket
>>> s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM, 0)
>>> addr_and_port = ('fe80::f816:3eff:fedb:ba4f', 8001)
>>> s.bind(addr_and_port)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python2.7/socket.py", line 224, in meth
    return getattr(self._sock,name)(*args)
socket.error: [Errno 22] Invalid argument
>>>
[1]+  Stopped                 python
[root@test ~]# netstat -anp | grep 8001
[root@test ~]#

One more update: I suppose the bind is failed due to my environment has some issue with IPv6 configuration. As I'm only able to get one IPv4 address by using "socket.getaddrinfo()" method.

Br, -Dapeng Jiao

Answer 1

You could get this error if attempted to bind the same socket more than once. But I can't see that is the case in your code.

That .openServerMode() method does no magic -- it just calls .bind() on socket object. For inspiration, does this work in at your Python prompt?

from pysnmp.carrier.asyncore.dgram import udp6

addr_and_port = ('fe80::a00:27ff:fe9e:9c16', 8001)
udp6.Udp6SocketTransport().openServerMode(addr_and_port)

or even:

import socket

s = socket.socket(socket.AF_INET6, socket.SOCK_DGRAM, 0)
addr_and_port = ('fe80::a00:27ff:fe9e:9c16', 8001)
s.bind(addr_and_port)

My hope is that tests like these may help you figuring out the problem...