A host with IP address 10.100.100.100 wants to use loopback testing,WHAT are the source and destination addresses?

Question

1. 10.100.100.100 & 10.100.100.100

2. 10.100.100.100 & 255.255.255.255

3. 10.100.100.100 & 127.1.100.1

4. 127.100.100.100 & 10.100.100.100

Answer 1

Loop Back testing means Source and Destination should be same.

So I suggest ANS is 1.

Comments

answer will be  a  3  . because here we are using a loopback testing for that we use a special ip address which may be 127. x.x .x but x can't be a 0 and 255

Answer 2

1 is the answer. 127.XXX are reserved for loopback though 127.0.0.1 is the usual implemented one (just a convention). 

http://en.utrace.de/whois/127.100.100.100

2 choice is broadcasting and hence cannot be the answer. 

Comments

Yes, it is implemented for you. Even for me it is implemented. But I have seen many sites saying it needn't be implemented by every one. So, if we have to pick one answer here, option 1 is better unless of course we have a strict argument against it.

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Option 1 is the answer. Works both ways :

$ ping --icmp --dest-ip 192.168.1.3 -S 127.0.0.1 -c 1

SENT (0.0310s) ICMP [127.0.0.1 > 192.168.1.3 Echo request (type=8/code=0) id=17069 seq=1] IP [ttl=64 id=52759 iplen=28 ]
RCVD (0.2122s) ICMP [192.168.1.3 > 127.0.0.1 Echo reply (type=0/code=0) id=17069 seq=1] IP [ttl=64 id=33614 iplen=28 ]
 
Max rtt: 181.075ms | Min rtt: 181.075ms | Avg rtt: 181.075ms
Raw packets sent: 1 (28B) | Rcvd: 1 (28B) | Lost: 0 (0.00%)

$ ping --icmp -S 192.168.1.3 --dest-ip 127.0.0.1 -c 1

SENT (0.0402s) ICMP [192.168.1.3 > 127.0.0.1 Echo request (type=8/code=0) id=62835 seq=1] IP [ttl=64 id=24034 iplen=28 ]
RCVD (0.2207s) ICMP [127.0.0.1 > 192.168.1.3 Echo reply (type=0/code=0) id=62835 seq=1] IP [ttl=64 id=47357 iplen=28 ]
 
Max rtt: 180.536ms | Min rtt: 180.536ms | Avg rtt: 180.536ms
Raw packets sent: 1 (28B) | Rcvd: 1 (28B) | Lost: 0 (0.00%)

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@Arjun Sir. As per me also it should be C because it is specifically made for loopback and if in linux u see Routing table for host it will show u loopback address set to 127.0.0.1.  Although we can remove or modify this entry but then unecessarily packet will go outside the system. But Loopack is only used to check working of all layers of TCP/IP

Answer 3

as there is given  for loopback testing then 3)127.1.100.1 is the right answer.

let me describe this in brief.

a. if u developed a software that is having client and server mechanism and u want test that on ur computer than  u can put loopback address at the destination and check for it without having any internet connection.

b.loopback address is done to check ur tcp/ip protocol and that works till network layer only.In this... packet is send by the network layer and received by that network layer only of the host .to make software to believe that they are connected to internet without actual connection.this is used to check proper functioning of upper layers only.

c.this loopback testing is done at ur computer so this destination address never ever be able to leave ur computer or host.

answer 1) is wrong as by this u can only test the internet connectivity of ur computer and u cant do loopback testing through this.

Answer 4

the answer is c . a can be the answer according to the definition of loopback . if u think loopback is going to the router and coming back then a will be the answer but in normal sense and actual practise the loopback is just making the  packet go and come back ut not to send to the link. so answer is c. in a packet will go to the router and then come back which may not be called loopback.