Successful Network Logon. Logon Type = 3. What is thi? How to block this?

Hi All,

I keep seeing some error regarding network logon. What is this? How can i block it?

Block incoming port 88?

Successful Network Logon:
     User Name:    username$
     Domain:        DOMAIN-NAME
     Logon ID:        (0x0,0x20C83F)
     Logon Type:    3
     Logon Process:    Kerberos
     Authentication Package:    Kerberos
     Workstation Name:    
     Logon GUID:    {9e5ce0f6-c05b-88a5-813c-b246d60da9bf}
     Caller User Name:    -
     Caller Domain:    -
     Caller Logon ID:    -
     Caller Process ID: -
     Transited Services: -
     Source Network Address:    xx.xx.xx.xx (some external IP)
     Source Port:    0

Thanks.