Discuss the SNMP Tools and describe the Command Tool in detail in your own language.

Discuss the SNMP Tools and describe the Command Tool in detail in your own language.

Answer

المطلوب اعادة صياغة للاجابة

SNMP Tools are tools used to get the MIB tree structure, as well as its values from a network element. There are three different types of SNMP MIB:

1. SNMP MIB browser uses a graphical interface to display the contents MIB of the different SNMP versions; it can also extract the data of private MIB objects.

2. a set of SNMP command-line tools, which is primarily UNIX- and Linux/FreeBSD-based tools. These tools generate SNMP messages, which are get, get-next, getbulk, set, response, and trap

3. snmpsniff, which is Linux/Free BSD based tool useful to read SNMP PDUs.

 

1.	SnmpGet	SNMP Get Command communicates with a network object using the SNMP get-request message .it’s used to retrieve data from a remote host given its host name, authentication information and an object identifier   The SNMP Get Command : snmpget [options] host community objectID [objectID] Where the host may be either a host name or an IP address.
2.	SnmpGetNext	SnmpGetNext is similar to snmpget except that it uses the SNMP get-next-request message. The managed object responds with the expected get-response message on the objectID that is lexicographically next to the one specified in the request.   SnmpGetNext command is especially useful to get the values of variables in an aggregate object, such as a table.
3.	SnmpTranslate	The snmptranslate utility is an application that translates one or more SNMP object identifier values from their symbolic (textual) forms into their numerical forms (or vice versa)
4.	snmpsniff	SNMP Sniff Tool captures SNMP packets going across the segment and stores them for later analysis.

 

 

 

Question two

Explain the secret and public-key cryptography schemes? Use small examples to illustrate your claims. Define the relative advantages of each scheme.

Answer

المطلوب اعادة صياغه للاجابة

Secret key cryptography

Both of the sender and the recipient use the same key to encrypt and decrypt the messages. The key has to be shared between the parties before data exchange which is considered a weakness point.

At the sender end, the encryption process is done by performing XOR between the plain text (original message) and the shared key to get the encrypted cipher message which will be sent to the recipient.

At the recipient end, the ciphered message is decrypted by performing XOR between the encrypted cipher message and the shared key to get the plain message.

Example:

Alice wants to send a message to Bob. Both Alice and Bob share the same secret key. To encrypt the message Alice XORs her message with the shared secret key. To decrypt the message Bob also XORs the message with his (the same) secret key.

 

The advantages of secret key cryptography are that

1. Performing XOR is very fast but not secure because the key need to be shared

2. It has been well tested.

Public-key cryptography schemes

A public-key cryptography scheme uses two different keys, one for encryption and one for decryption. Each communicating entity will have its own key pair (public and a private key); the private key will be kept secret and the public key will be made freely available. The message is encrypted by one key and decrypted by the other key. Public key algorithms can allow either the public key or the private key to be used for encryption with the remaining key used for decryption.

 

Example

In order for Alice to send Bob a message she first needs to obtain his public key. Bob’s public key will be shared on his homepage for anyone to download or any other method. Alice obtains his public key, encrypts a message using bob’s public key and then sends it to Bob. Bob decrypts the message using his own private key to get the original message.

Advantages: من الافضل اختيار تلات فقط واعادة صياغتها

1. Only one part of the key must be kept secret (the public key) and there is no way to drive the private key from the public key.

2. There is no need to change your public/private key pair (unless someone finds your public key)

3. There is no need for initial key exchange as in secret key cryptography

4. It can serve as a digital signature

5. More secure since no exchange of keys is required before data exchange but it’s slower than shared keys system

 

 

Question three

The auto- discovery in some NMSs is through by the network management system starting with an ARP query to local router. In what way would you determine the IP address of the local router?

نختار اجابة ونعيد صياغتها

Answer 1

The arp query on the local host of NMS in addition to the ARP cache would contain the router IP-MAC address. The router could also be discovered by doing traceroute, and identifying the gateway out of the subnetwork.

Answer 2

The localhost running the network management system sends an ARP query asking about the physical address of the local router, the ARP query contains four addresses as follows:

1. The MAC address of the local host.

2. The MAC address of the receiptient is FF:FF:FF:FF:FF:FF or 1’s.

3. The IP address of the local host.

4. The IP address of the local router

The local router responds to the ARP query by sending a unicast ARP response that contains its MAC address. The router’s IP and MAC addresses will be added to the ARP cache table that contains the addresses of all the recently communicated hosts and nodes. So it’s clear that the local host already knows the local router’s IP and uses it in the ARP query and stores it inside its ARP cache.

 

Question four

The network shown in the figure is an MPLS network with all router configured as Label Switching Routers (LSRs). The paths (LSPs) are determined using Traffic Engineering (TE). Fill in the R2 routing table (a) for the path with no tunnel and (b) for the path with tunnel T1. The address of each router is x.x.x.x where x is the router number e.g. 1.1.1.1.

a. Routing Table R2 without Tunnel

Destination	Output Interface	Next Hop	Metric
1.1.1.1	I1	1.1.1.1	1
3.3.3.3	I3	3.3.3.3	1
4.4.4.4	I4	4.4.4.4	1
5.5.5.5	I3	3.3.3.3	2
6.6.6.6	I4	4.4.4.4	2

 

 

b. Routing Table R2 with Tunnel

Destination	Output Interface	Next Hop	Metric
1.1.1.1	I1	1.1.1.1	1
3.3.3.3	I3	3.3.3.3	1
4.4.4.4	I4	4.4.4.4	1
5.5.5.5 5.5.5.5	T1 I3	6.6.6.6 3.3.3.3	2 2
6.6.6.6	T1	6.6.6.6	2/1