Network Training: Network Interview Question and Answer

Question 31 : What is Etherchannel and purpose?

Answer : Etherchannel is a bunch of links (at least 2) bundled together to have more throughput, more bandwidth. so if u have 2 trunk links between switches A and B, STP will block one of those. if u put those 2 links inside of a etherchannel, STP will not block any links. Think of etherchannel as "fat" multilink ; and one link in case of STP.

redundancy - if one of links fails inside of etherchannel, etherchannel is still up up;it does not even go down and up; STP cost will change and STP may re-calculate path to root.

reliability -same as above when one of many link fails, etherchannel is still up

bettwer throughput, more bandwidth - if u bandle 4 links of 100Mbps per one link, in full duplex -I think- u get 800Mbps of throughput/bandwidth.

and yes for trunks; etherchannels are trunks. in addition to L2, there are also Layer 3 etherchannels (one with Ip address assigned per etherchannel)

Question 32 : How to avoid this error " Translating"?

Example : Switch>
Switch>blah
Translating "blah"...domain server (255.255.255.255)

Answer : Hold down the keys, together: Ctrl+Shift+6

To avoid the problem in the future, use the configuration command of:

no ip domain lookup

Question 33 :NAT Translation debug? what the "*" next to the second and remaining "NAT" lines means ?

Example :

05:32:23: NAT: s=10.10.50.4->172.16.11.70, d=172.16.11.7 [70]

05:32:23: NAT*: s=172.16.11.7, d=172.16.11.70->10.10.50.4 [70]

05:32:25: NAT*: s=10.10.50.4->172.16.11.70, d=172.16.11.7 [71]

05:32:25: NAT*: s=172.16.11.7, d=172.16.11.70->10.10.50.4 [71]

05:32:27: NAT*: s=10.10.50.4->172.16.11.70, d=172.16.11.7 [72]

05:32:27: NAT*: s=172.16.11.7, d=172.16.11.70->10.10.50.4 [72]

Answer : An asterisk (*) indicates that the translation is occurring in the fast path. The first packet in a conversation always goes through the slow path (that is, it is process switched). The remaining packets go through the fast path if a cache entry exists.

Question 34 : What does ip subnet-zero command do?

Example : 50.0.0.0/10

Possible subnets are:

50.0000 0000.x.x (first subnet)

50.0100 0000.x.x

50.1000 0000.x.x

50.1100 0000.x.x (last subnet)

Answer : It was not allowed to use the all 00 (the first subnet above, also called "subnet zero") subnet, as the subnet bits were all zeros. In that same thinking, it was not allowed to assign last subnet, were all 1's.

The "subnet-zero" command really should be called: "Go ahead and use the all zeros and all ones subnets (first and last)".

The subnet-zero would allow 4 subnets above to be used instead of just 2. This command is the default on current IOS, and doesn't need to be added to the configuration.

Here is an example. Without the use of the subnet-zero, it won't allow us to assign an IP address in the first subnet (subnet zero):

R1(config)#no ip subnet-zero

R1(config)#int loopback 1

R1(config-if)#ip address 50.0.0.1 255.192.0.0

Bad mask /10 for address 50.0.0.1

If we add the subnet-zero command back into the configuration, now it allows an IP address to be assigned from that subnet:

R1(config)#ip subnet-zero

R1(config)#int loopback 1

R1(config-if)#ip address 50.0.0.1 255.192.0.0

Question 35 : What are the Security threats and Examples?

Two Types

i. outside the network

ii. inside the network

The threats from inside the network are:

abuse of user rights
authentication and authorization issues
information leakage to unauthorized people

Threats from the internet, outside our network:

spam and phishing messages
malicious codes in mail
trojan, malware, worms
password sniffing and cracking attacks
network scanning for exploits
DDoS attacks

Question 36 : What is the meaning of “Line is up, protocol is down”?

Layer 2 connection between two switches you're operating with 2 layers. The line is UP and Protocol is Down means, Layer 1 (Physical connectivity is correct. But, the Layer 2 negotiation is not success.

This could be caused by Duplex or Speed mismatch, a unidirectional link of some type, a hardware/software failure on the switch, or the other side could be err-disabled or shutdown on the other side. This could also be a problem if different protocols are used for trunking(ISL vs dot1q).

Question 37 : How many subnets and hosts per subnet can you get from the network 10.0.0.0 255.255.240.0?

This question for you friends... Please answer....