Network Engineer Interview Questions and Answers by rafomac

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1. Interviewer: What is a default Route?

-Well a default route is the route that a packet will take when no other routes are specified in the Routers route table.

2. Layers of the OSI model:

3. Ports:
LDAP 389
POP3 110
IMAP 143
RDP 3389

4. Class Ranges:
A 1 -126
B 128 -191
C 192 -223
D 224 -239

E 240 -255

5. Purpose of:
DNS  -Maps URL to IP
DHCP – Reservation system for IP

6. Describe the 7 layers of the
OSI model 

-Physical – The physical layer consists of the basic networking hardware transmission technologies of a network.
-Data Link – MAC responsible for media access control, flow control and error checking
-Network – (IP) The network layer is responsible for packet forwarding including routing through intermediate routers
-Transport – (TCP/UDP) the Transport layer ensures the reliable arrival of messages and provides error checking mechanisms and data flow controls
-Session – This layer establishes, manages and terminates connections between applications.

-Presentation – This layer formats and encrypts data to be sent across a network. Works by transforming data into a format that can be accepted by the Application Layer.

-Application This layer supports application and end-user processes. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

7. Explain what an OSPF area.
– Open Shortest Path First (OSPF) is a link-state routing protocol for Internet Protocol (IP) networks.
-An OSPF network may be structured, or subdivided, into routing areas to simplify administration and optimize traffic and resource utilization.

8. Explain what happens when a device comes onto the network and requests a DHCP lease
-The clients request configuration settings using the DHCP protocol such as an IP address, a default route and one or more DNS server addresses. Once the client implements these settings, the host is able to communicate on that internet. DHCP provide IP address automatically.

9. Describe IP Sec
-Internet Protocol Security = IPSec is a technology protocol suite for securing Internet Protocol (IP) communications by authenticatingand/or encrypting each IP packet of a communication session.

10. Describe IKE phase 1 and phase 2
Internet Key Exchange (IKE and IKEv2) Is the key to setup a Security Association (SA) which is a shared security attribute between two network entities to support secure communication, such as cryptographic alogorithm and mode, traffic encryption key, and parameters for the network data to be passed over the connection.

 11. Explain what a VLAN is
-Network architects set up VLANs to provide the segmentation services traditionally provided only by routers in LAN configurations. 
-VLANs address issues such as scalability, security, and network management
12. Explain a trunk port
-Trunks are used to interconnect switches to form networks, and to interconnect local area networks (LANs) to form wide area networks (WANs) or virtual LANs (VLANs). 
-These ports are capable of carrying traffic for any and ALL VLANs accessible by a switch 
13. Explain an access port
-In contrast to a trunk port which carries traffic to all VLANs an access port carries traffic to and from the specific VLAN assigned to it
14. Explain what a spanning tree protocol is
-So the Spanning Tree Protocol (STP) is a network protocol that ensures a loop-freetopology for any bridged Ethernet local area network.

15. What is the root bridge?
-The root bridge of the spanning tree is the bridge with the smallest (lowest) bridge ID. Determined by the Bridge ID and the MAC address

16. Describe how a switch determines how to send a packet to its destination
-Well a switch which exists at Layer 2 uses the media access control address (MAC address) from the host’s network interface cards (NICs) to decide where to forward frames
17. On a Linux system what command do you use to check the systems IP Address?
Note:  Memorize If as Interface
18. Describe TCP Handshake:

For example, when your computer visits, it does a TCP Handshake on the standard HTTP port, port 80, data is transfered, then the connection is closed.

The client connects on port 80 with a SYN (Synchronize) and the server replies with an ACK (Acknowledge) and another SYN (Synchronize). The client will reply with a final ACK (Acknowledge), this completes the handshake.

A client and server going through a TCP Handshake looks like this:
Client: SYN
Server: ACK/SYN
Client: ACK

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