Network Management and O&M (SNMP, NTP, Telnet/SSH, FTP/TFTP, Syslog)
SNMP
SNMP has a manager (NMS) and an agent on the device. The MIB is the tree of managed objects and SMI defines the data types. SNMPv1 and v2c authenticate with a plaintext community string (read-only or read-write); v2c adds GetBulk and 64-bit counters but still no security; v3 adds user-based security with authentication (MD5/SHA) and privacy/encryption (DES/AES). The agent listens on UDP 161; traps and informs go to the manager on UDP 162. Informs are acknowledged, traps are not.
NTP
NTP synchronises clocks over UDP 123. Stratum 0 is a reference clock, stratum 1 is directly attached, and stratum 16 means unsynchronised. Devices can be a unicast server/client, symmetric peer, or broadcast/multicast. Accurate time matters because syslog timestamps, certificates, and accounting records depend on it.
Remote access and file transfer
Telnet (TCP 23) sends everything in clear text; SSH (TCP 22) encrypts and is the correct choice, and NETCONF runs over SSH on TCP 830. Local console access is out-of-band. FTP uses TCP 20/21 with authentication, TFTP uses UDP 69 with no authentication - use TFTP only on trusted management networks. VRP user privilege levels run from 0 (visit) to 15 (managing).
Syslog
Severity levels, lowest to highest number: 0 emergency, 1 alert, 2 critical, 3 error, 4 warning, 5 notification, 6 informational, 7 debugging. Logs can go to console, monitor, buffer, file or a syslog server; info-center controls which levels are captured.
Rule of thumb
If the question asks for the most secure option, pick SSH over Telnet, SNMPv3 over v2c, and SCP/SFTP over TFTP; if it asks for delivery guarantee of event messages, pick informs.