System Administration FAQ questions

E-Mail Servers and Ports

Incoming Mail Server (POP3, IMAP, HTTP): The incoming mail server is the server associated with an email address account. There cannot be more than one incoming mail server for an email account.

Outgoing Mail Server (SMTP): Most outgoing mail servers use SMTP (Simple Mail Transfer Protocol) for sending emails. The outgoing mail server can belong to your ISP or to the server where you setup your email account.

The main email ports are:
POP3 – port 110
IMAP – port 143
SMTP – port 25
HTTP – port 80
Secure SMTP (SSMTP) – port 465
Secure IMAP (IMAP4-SSL) – port 585
IMAP4 over SSL (IMAPS) – port 993
Secure POP3 (SSL-POP) – port 995

Forests, Trees, And Domains

Forests, trees, and domains are the logical divisions in an Active Directory network.

A domain is defined as a logical group of network objects (computers, users, devices) that share the same active directory database.

A tree is a collection of one or more domains and domain trees in a contiguous namespace linked in a transitive trust hierarchy.

At the top of the structure is the forest. A forest is a collection of trees that share a common global catalog, directory schema, logical structure, and directory configuration. The forest represents the security boundary within which users, computers, groups, and other objects are accessible.

What Are Lingering Objects?

A lingering object is a deleted AD object that still remains on the restored domain controller in its local copy of Active Directory. They can occur when changes are made to directories after system backups are created.

When restoring a backup file, Active Directory generally requires that the backup file be no more than 180 days old. This can happen if, after the backup was made, the object was deleted on another DC more than 180 days ago.

When a DC deletes an object it replaces the object with a tombstone object. The tombstone object is a placeholder that represents the deleted object. When replication occurs, the tombstone object is transmitted to the other DCs, which causes them to delete the AD object as well.

Tombstone objects are kept for 180 days, after which they are garbage-collected and removed.

If a DC is restored from a backup that contains an object deleted elsewhere, the object will re-appear on the restored DC. Because the tombstone object on the other DCs has been removed, the restored DC will not receive the tombstone object (via replication), and so it will never be notified of the deletion. The deleted object will “linger” in the restored local copy of Active Directory.

How to Remove Lingering Objects

You can manually remove lingering objects using the console utility REPADMIN.EXE. Use the option /removelingeringobjects.

Differentiate Between Ntfs , exFAT & Fat32

NTFS is the current file system used by Windows. It offers features like security permissions (to limit other users’ access to folders), quotas (so one user can’t fill up the disk), shadowing (backing up) and many other features that help Windows.

FAT32 is the older Microsoft filesystem, primarily used by the Windows 9X line and Window could be installed on a FAT32 partition up to XP. In comparison, FAT32 offers none of what was mentioned above, and also has a maximum FILE (not folder) size of 4GB.

Extended File Allocation Table (exFAT) – designed to be a lightweight file system like FAT32, but without the extra features and over head of NTFS and without the limitations of FAT32.

What is Apipa?

Stands for Automatic Private IP Addressing

APIPA is a DHCP fail over mechanism for local networks. With APIPA, DHCP clients can obtain IP addresses when DHCP servers are non-functional. 

APIPA exists in all modern versions of Windows except Windows NT.  When a DHCP server fails, APIPA allocates a class B IP addresses in the private range 169.254.0.1 to 169.254.255.254.

Wins Server

Windows Internet Name Service (WINS) servers dynamically map IP addresses to computer names (NetBIOS names). This allows users to access resources by computer name instead of by IP address. If you want this computer to keep track of the names and IP addresses of other computers in your network, configure this computer as a WINS server.

If you do not use WINS in such a network, you cannot connect to a remote network resource by using its NetBIOS name.

Today, DNS has replaced WINS, since Microsoft made changes to NetBIOS, allowing it to use the TCP/IP stack to perform its job (NetBIOS over TCP/IP) and most DNS servers are able to handle NetBIOS requests. This is why WINS servers are becoming lesser day by day.
In short, DNS maps TCP/IP hostnames to IP addresses and WINS maps NetBIOS hostnames to IP addresses.
Something more

First of all, I thank all the people, companies and organizations for bringing this know How! The content and works published on this post are governed by the respective person, company or organization.

mm

Anup Chhetri

IT system administrator

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