tcpdump to capture snmp packets

listen-snmp.sh

tcpdump -i eno1 -T snmp -n dst portrange 161-162
# output looks like this for an ios router linkup
# 11:47:50.905818 IP 10.10.201.27.56503 > 10.10.202.11.162:  V2Trap(138)  .1.3.6.1.2.1.1.3.0=791308 .1.3.6.1.6.3.1.1.4.1.0=.1.3.6.1.6.3.1.1.5.4 .1.3.6.1.2.1.2.2.1.1.1=1 .1.3.6.1.2.1.2.2.1.2.1="FastEthernet0/0" .1.3.6.1.2.1.2.2.1.3.1=6 .1.3.6.1.4.1.9.2.2.1.1.20.1="up"

# in ios you can see how many snmp traps, the address its sending to and the port
# router4#show snmp
# Chassis: FTX151202SZ
# 0 SNMP packets input
#     0 Bad SNMP version errors
#     0 Unknown community name
#     0 Illegal operation for community name supplied
#     0 Encoding errors
#     0 Number of requested variables
#     0 Number of altered variables
#     0 Get-request PDUs
#     0 Get-next PDUs
#     0 Set-request PDUs
#     0 Input queue packet drops (Maximum queue size 1000)
# 12 SNMP packets output
#     0 Too big errors (Maximum packet size 1500)
#     0 No such name errors
#     0 Bad values errors
#     0 General errors
#     0 Response PDUs
#     12 Trap PDUs
# SNMP Dispatcher:
#    queue 0/75 (current/max), 0 dropped
# SNMP Engine:
#    queue 0/1000 (current/max), 0 dropped
# 
# SNMP logging: enabled
#     Logging to 10.10.202.11.162, 0/10, 12 sent, 0 dropped.

# ios was configured with
# router4(config)# snmp-server community public RO
# router4(config)# snmp-server enable traps snmp linkdown linkup
# router4(config)# snmp-server host 10.10.202.11 version 2c public