Subnetting

Subnetting



 What valid host range is the IP address 172.31.238.81/21 part of?

Subnetting Question Two

What is the maximum number of subnets and hosts per subnet achievable from the network 172.27.0.0/28?

Q1/ 172.31.238.0 =network ip , 172.31.238.1 to 172.31.239.254 Valid Host Range & 172.31.239.255 Gateway ip

1) valid host range 172.31.232.1- 172.31.239.254 .... 2) number of subnet 4096 n host per subnet 14

Q2, 172.27.0.0/28 subnet mask 255.255.248.0
You borrowed 12 bits, so you can create 4096 network with 8 host every network.

CCNA Teacher

CCNA Teacher


While configuring NAT on a CISCO router , we use "ip nat inside source" command.I do understand this.But what happens if i use "ip nat outside source" command.What does this command do?

Basically changes the source address of packets that are traveling from the outside to the inside, so the opposite of the inside command. It will also change the destination address of packets going in the opposite direction. I've not personally used it however its use would stem from when inside addresses are overlapping with addresses that are on the outside of your network which comes from for example people using public IP ranges on their internal network which have been assigned for use online somewhere else.


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Please look at this scenario :
In this simple scenario we would like to put an ACL in the router by which just PC1 would be allowed to telnet to the router.
To do this scenario
after creating ACL by these commands :
Router(config)# ip access-list standard amir
Router(config-std-nacl) # 10 permit host 192.168.10.2
then I recall this ACL on the fa0/0 of Router by these commands :
Router(config)# line vty 0 4
Router(config-line) # ip access-class amir in

But after all these commands and using Packet tracer as a simulator software, both of PCs are able to telnet to the router !! it is not supposed that PC0 (192.168.10.1) will be able to telnet the router. So what is the wrong with those commands ?

if I put that ACL on the interface f0/0 instead of line vty, and using these commands :
Router(config)# int f0/0
Router(config-if) # ip access-group amir in

the scenario will work well .
so I don't know the problem is related to my commands or to Packet tracer as a simulator.
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using number instead of name for ACL didn't work out (in fact I had tried that before I wrote this post) , but using "deny any" worked out even for a named ACL. the point is all of these stories and problems just happend in Packet tracer as a simulator , but you won't face any problem with those command by using GNS3 as a emulator.
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 use out at the end of your command .and also first configur telnet in router.then define access list.

It's not a PT bug! It works fine for me without a deny any at the end of the ACL and applied on the vty line with the access-class command. And I know that it worked fine as back as v4 and we are on 6.1.1 now.

what is the function of two sublayer of data link layer

what is the function of two sublayer of data link layer ???

There are two sub-layers in Data link Layer that is Mac layer and Logical link layer.MAC defines how packets are placed on the media. LLC is responsible for identifying Network Layer protocols and encapsulating them..LLC header tells the data link layer,what to do with a packet once a frame is received.

CCNA EXAM PAPER

1. Which of the following descriptions are true regarding the management connections on a Cisco router? (Choose three.)
- They are non-network connections.
They are used to connect the router to the rest of the production network.
They are synchronous serial ports.
- They are used for initial router configuration.
- They are asynchronous serial ports.
They are accessed using their assigned IP address.

2. The console port can be used for which of the following? (Choose three.)
- debugging.
- password recovery.
routing data between networks.
- troubleshooting.
connecting one router to another.

3. Which of the following describes the function of a WAN?
connects peripherals in a single location.
connects multiple networks in a single building.
provides connectivity on a LAN.
- provides connectivity over a large geographic area.

4. An internetwork must include which of the following? (Choose three.)
- switching.
static addressing.
IETF standardization.
- dynamic or static routing.
- consistent end-to-end addressing.

5. ABC Company just purchased three new routers to start their company network. Which items are needed to establish a terminal session between a PC and the router for the initial configuration? (Choose three.)
straight-through cable.
- terminal emulation software.
- rollover cable.
- RJ-45 to DB-9 connector.
V.35 cable.

6.Terminal emulation software, such as HyperTerminal, can be used to configure a router. Which of the following HyperTerminal options shown in the graphic are correctly set to allow configuration of a Cisco router? (Choose three.)
bits per second.
- data bits.
- parity.
- stop bits.
flow control.

7. Which of the following devices are used in the construction of a WAN? (Choose three.)
hubs.
- routers.
- communication servers.
transceivers.
- modems.
multi-port repeaters.

8. Which of the following are functions of RAM? (Choose three.)
contains startup configuration file.
- stores routing table.
- holds fast switching cache.
retains contents when power is removed.
- stores running configuration file.

9. Why is a console connection to a router or switch preferred when troubleshooting? (Choose two.)
can be accessed remotely.
- does not depend on network services.
- displays startup and error messages by default.
does not require special components.

10. Which basic components do a router and a standard desktop PC have in common? (Choose three.)
- CPU.
hard drive.
- input/output interfaces.
keyboard.
monitor.
- system bus.

11. During the initial configuration of a 2600 series Cisco router, which cable is required for connecting a PC to the console port?
twisted.
crossover.
- rollover.
straight.

12. A router is composed of many internal components. Which of the following components stores a copy of the router's configuration file?
metal-oxide memory.
read only memory.
flash memory.
- non-volatile random access memory.

13. What contains the instructions that a router uses to control the flow of traffic through its interfaces?
packet configuration.
- configuration files.
flash memory.
internal components.

14. Several Ethernet hosts on a LAN need the gateway services of a Cisco 2500 series router. Which of the following would be needed to physically connect a router to all of the hosts on the LAN? (Choose two.)
a crossover cable between the transceiver on a router and a switch.
a crossover cables between a switch and hosts on a LAN.
a straight-through cable between the auxiliary port on a router and a switch.
a rollover cable between the console port on a router and a switch.
- straight-through cables between a switch and hosts on a LAN.
- a straight-through cable between the transceiver on a router and a switch.

15. Which router component holds the configuration file when power is lost?
volatile random access memory.
read only memory.
- non-volatile random access memory.
flash memory.

16. Which of the following layers of the OSI model are incorporated in WAN standards? (Choose two.)
- physical layer.
application layer.
transport layer.
- data link layer.
session layer.

17. Which of the following are true regarding router interfaces? (Choose three.)
provide temporary memory for the router configuration files.
- connect the router to the network for packet entry and exit.
- can be on the motherboard or a separate module.
hold the IOS image.
- connect the router to LANs and WANs.

18. Which of the following tasks can be accomplished through a management connection on a router? (Choose three.)
- troubleshooting problems.
- monitoring the system.
capturing LAN data packets.
- configuring the router.
routing data packets.

19. What do routers use to select the best path for outgoing data packets?
ARP tables.
bridging tables.
- routing tables.
switching tables.

20. Which of the following are functions of NVRAM? (Choose two.)
stores the routing table.
- retains contents when power is removed.
- stores the startup configuration file.
contains the running configuration file.
stores the ARP table.

21. Select the statements that correctly describe flash memory in a 2600 series router? (Choose two.)
holds the startup configuration by default.
- can be upgraded with single in-line memory modules.
- stores Cisco IOS software images.
stores routing table information by default.
maintains the only copy of an IOS image after the router is booted.

OSI MODEL

OSI MODEL

The OSI (Open Systems Interconnection) was created by the International Organisation for Standardisation (ISO) as a framework used to describe how data is transferred over a medium from one networked device to another. It is made up of 7 layers:

• 7. Application
• 6. Presentation
• 5. Session
• 4. Transport
• 3. Network
• 2. Data Link
• 1. Physical

The 4 main advantages of the OSI are:

1. It divides the communication process into simpler components, aiding component development, design, and troubleshooting.
2. It encourages industry standardization by defining what functions occur at each layer of the model.
3. It prevents changes in one layer from affecting other layers, so that it does not hamper development.
4. It allows various types of network hardware and software to communicate.

Port & Socket numbers

Port & Socket numbers

A port number is a number that identifies different services that run on a PC or device using TCP or UDP (layer 4), while a socket number is an IP address with the port number included: eg. 192.168.0.10:21

Port numbers are assigned by the IANA (Internet Assigned Numbers Authority)

There a 3 different types of port numbers :
Well known Ports (1 - 1023) - Used for common services such as FTP, HTTP, Telnet, DHCP.
Registered Ports (1024 - 49151) - Used for services that are not as commonly used that they warrant a well known port number. Eg. WAP, MS SQL, World of Warcraft.
Private/Dynamic Ports (49152 - 65535) - Ports that can be used by anyone for any purpose.

You can view ports that are currently being used on your PC by typing 'netstat' into the DOS prompt (as seen below a after colon in private/public address).

What is a socket?
The combination of a source IP address and port number or a destination IP address and port number
the combination of the source and destination sequence numbers and port numbers
the combination of the source and destination sequence and acknowledgment numbers
the combination of the source and destination IP address and source and destination Ethernet address


A TCP socket is an endpoint instance defined by an IP address and a port in the context of either a particular TCP connection or the listening state.
A port is a virtualisation identifier defining a service endpoint (as distinct from a service instance endpoint aka session identifier).
A TCP socket is not a connection, it is the endpoint of a specific connection.
There can be concurrent connections to a service endpoint, because a connection is identified by both its local and remote endpoints, allowing traffic to be routed to a specific service instance.

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