Perl Net-SNMP SNMP v3 compatibility Auth & Priv support matrix

Configuration

• User: xorux
• Password: xorux4you
• Security level: AuthPriv
• Priv protocol: AES128
• Auth protocol: SHA

configure terminal
snmp-server protocol enable

# check available auth algorithms
snmp-server user xormon auth ?
  md5  Use HMAC MD5 algorithm for authentication
  sha  Use HMAC SHA algorithm for authentication

# use SHA and check available privacy algorithms
snmp-server user xormon auth sha xorux4you priv ?
  aes-128  Use 128-bit AES algorithm for privacy

# use AES-128, complete command should look like this
snmp-server user xormon auth sha xorux4you priv aes-128 xorux4you

# end configuration with Ctrl+Z

Test:

snmpwalk -v 3 -l authPriv -u xormon -A xorux4you -X xorux4you -a SHA -x AES 192.168.1.1:161 sysDescr
  SNMPv2-MIB::sysDescr.0 = STRING: "Cisco NX-OS(tm) m9100, Software (m9100-s2ek9-mz) ...

Notes

• Auth and Priv passwords must have at least 8 characters
  
• Use preferably AES128 if you are not sure that your Operating System supports higher AES in snmp-perl module
  Note that snmpwalk might work, just problem could be snmp-perl module only as it has different support matrix
  
• When using AES256 privacy protocol, at least SHA256 must be used as authentication protocol
  

DES vrs AES

Do not use old DES protocol, use AES instead.
New Linuxes do not support DES protocol anyway, you might check if your operating systems supports it or does not
If bellow cmd prints anything then DES is supported and you can use it, but try to avoid that

openssl ciphers | grep  DES

Add SAN switch to XorMon