introduce
SNMP stands for simple network management protocol. This is a way for servers to share information about their current status and a channel for administrators to modify predefined values. SNMP is a protocol implemented on the application layer of the network stack (click here to learn about the network layer). The protocol was created to collect information from very different systems in a consistent manner.
You can read more about SNMP, OID, and SNMP methods in the links above. To summarize, the script uses:
- snmp version 2c
- snmp walk is the main method to obtain data from snmp
- The data obtained from the device is obtained from a specific OID (more lldp OIDs can be found in here (found)
Link Layer Discovery Protocol( LLDP ) It is a vendor neutral layer 2 protocol. Sites connected to a specific LAN segment can use this protocol to announce their identity and functions, and receive the same information from physically adjacent layer 2 peers.
Using python to combine SNMP and LLDP
The purpose of my program is to return the neighbor data (local and remote ports + neighbor name) of all switches in the file by using Python 3.6 and providing a switch data file (community string, snmp port and switch ip).
Sample profile:
community_string1, snmp_port1, ip1 community_string2, snmp_port2, ip2 community_string3, snmp_port3, ip3
Sample output:
[
{
"name1": {
"ip": "ip1",
"neighbours": [
{
"neighbour_name1": "neighbour_name1",
"local_port1": "local_port1",
"remote_port1": "remote_port1"
},
{
"neighbour_name2": "neighbour_name2",
"local_port2": "local_port2",
"remote_port2": "remote_port2"
},
{
"neighbour_name3": "neighbour_name3",
"local_port3": "local_port3",
"remote_port3": "remote_port3"
},
]
},
"name2": {data here},
"name3": {data here},
}
]
Interpretation output
- name1 represents the switch name in the first line of the configuration file (retrieve PARENT_NAME_OID by executing snmp walk for)
- ip1 The first line from the configuration file represents the IP of the switch (this is obtained from the configuration file)
- Neighbors are retrieved through snmp using a specific OID (see the following code).
I think this JSON output format is the most relevant, but if you have a better idea, I'd like to hear it.
code
Now, the code is a little messy, but it uses pysnmp You can use pip It receives the configuration file as a CLI parameter, parses it, and processes the information in it.
import argparse
import itertools
import os
import pprint
from pysnmp.hlapi import *
NEIGHBOUR_PORT_OID = '1.0.8802.1.1.2.1.4.1.1.8.0'
NEIGHBOUR_NAME_OID = '1.0.8802.1.1.2.1.4.1.1.9'
PARENT_NAME_OID = '1.0.8802.1.1.2.1.3.3'
class MissingOidParameter(Exception):
"""
Custom exception used when the OID is missing.
"""
pass
def is_file_valid(filepath):
"""
Check if a file exists or not.
Args:
filepath (str): Path to the switches file
Returns:
filepath or raise exception if invalid
"""
if not os.path.exists(filepath):
raise ValueError('Invalid filepath')
return filepath
def get_cli_arguments():
"""
Simple command line parser function.
"""
parser = argparse.ArgumentParser(description="")
parser.add_argument(
'-f',
'--file',
type=is_file_valid,
help='Path to the switches file'
)
return parser
def get_switches_from_file():
"""Return data as a list from a file.
The file format is the following:
community_string1, snmp_port1, ip1
community_string2, snmp_port2, ip2
community_string3, snmp_port3, ip3
The output:
[
{"community": "community_string1", "snmp_port": "snmp_port1", "ip": "ip1"},
{"community": "community_string2", "snmp_port": "snmp_port2", "ip": "ip2"},
{"community": "community_string3", "snmp_port": "snmp_port3", "ip": "ip3"},
]
"""
args = get_cli_arguments().parse_args()
switches_info = []
with open(args.file) as switches_info_fp:
for line in switches_info_fp:
line = line.rstrip().split(',')
switches_info.append({
'community': line[0].strip(),
'snmp_port': line[1].strip(),
'ip': line[2].strip(),
})
return switches_info
def parse_neighbours_ports_result(result):
"""
One line of result looks like this:
result = iso.0.8802.1.1.2.1.4.1.1.8.0.2.3 = 2
Where the last "2" from the OID is the local port and the value
after '=' is the remote port (2)
"""
if not result:
raise MissingOidParameter('No OID provided.')
value = result.split(' = ')
if not value:
return 'Missing entire value for OID={}'.format(result)
else:
oid, port = value
local_port = re.search(r'{}\.(\d+)'.format(NEIGHBOUR_PORT_OID[2:]), oid).group(1)
if port:
remote_port = re.search(r'(\d+)', port).group(1)
else:
remote_port = 'Unknown'
return 'local_port', local_port, 'remote_port', remote_port
def parse_parent_name(result):
"""
One line of result looks like this:
result = iso.0.8802.1.1.2.1.3.3.0 = Switch01
The name of the parent is "Switch01"
"""
if not result:
raise MissingOidParameter('No OID provided.')
value = result.split(' = ')
if not value:
return 'Missing entire value for OID={}'.format(result)
else:
return 'Unknown' if not value[-1] else value[-1]
def parse_neighbour_names_results(result):
"""
One line of result looks like this:
result = iso.0.8802.1.1.2.1.4.1.1.9.0.2.3 = HP-2920-24G
The name of the parent is "Switch01"
"""
if not result:
raise MissingOidParameter('No OID provided.')
value = result.split(' = ')
if not value:
return 'Missing entire value for OID={}'.format(result)
else:
return ('name', 'Unknown') if not value[-1] else ('name', value[-1])
def main():
data = {}
switches_filedata = get_switches_from_file()
for switch in switches_filedata:
community = switch.get('community')
snmp_port = switch.get('snmp_port')
ip = switch.get('ip')
name = ''
for (error_indication, error_status, error_index, var_binds) in nextCmd(
SnmpEngine(),
CommunityData(community),
UdpTransportTarget((ip, snmp_port)),
ContextData(),
ObjectType(ObjectIdentity(PARENT_NAME_OID)),
lexicographicMode=False
):
# this should always return one result
name = parse_parent_name(str(var_binds[0]))
if not name:
print('Could not retrieve name of switch. Moving to the next one...')
continue
neighbour_names = []
neighbour_local_remote_ports = []
for (error_indication, error_status, error_index, var_binds) in nextCmd(
SnmpEngine(),
CommunityData(community),
UdpTransportTarget((ip, snmp_port)),
ContextData(),
ObjectType(ObjectIdentity(NEIGHBOUR_NAME_OID)),
lexicographicMode=False
):
for var_bind in var_binds:
neighbour_names.append(
parse_neighbour_names_results(str(var_bind))
)
for (error_indication, error_status, error_index, var_binds) in nextCmd(
SnmpEngine(),
CommunityData(community),
UdpTransportTarget((ip, snmp_port)),
ContextData(),
ObjectType(ObjectIdentity(NEIGHBOUR_PORT_OID)),
lexicographicMode=False
):
for var_bind in var_binds:
neighbour_local_remote_ports.append(
parse_neighbours_ports_result(str(var_bind))
)
neighbours = []
for a, b in itertools.zip_longest(
neighbour_names,
neighbour_local_remote_ports,
fillvalue='unknown'
):
neighbours.append({
a[0]: a[1],
b[0]: b[1],
b[2]: b[3]
})
data[name] = {
'ip': ip,
'neighbors': neighbours
}
return data
if __name__ == '__main__':
all_data = main()
pprint.pprint(all_data, indent=4)
snmp-lldp.py -f snmp-lldp.txt