Question from a test

jambla85

I am slightly confused by a question I have come across.

By looking at the following output, which of the following commands would allow dynamic translations?
Router#show ip nat trans
Pro Inside global Inside local Outside local Outside global
--- 1.1.128.1 10.1.1.1 --- ---
--- 1.1.130.178 10.1.1.2 --- ---
--- 1.1.129.174 10.1.1.10 --- ---
--- 1.1.130.101 10.1.1.89 --- ---
--- 1.1.134.169 10.1.1.100 --- ---
--- 1.1.135.174 10.1.1.200 --- ---

a) ip nat inside source pool todd 1.1.128.1 1.1.135.254 prefix-length 1
b) ip nat pool todd 1.1.128.1 1.1.135.254 prefix-length 19
c) ip nat pool todd 1.1.128.1 1.1.135.254 prefix-length 18
d)ip nat pool todd 1.1.128.1 1.1.135.254 prefix-length 16

Answer
What we need to figure out for this question is only the inside global pool. Basically, we start at 1.1.128.1 and end at 1.1.135.174; our block size is 64 in the third octet, or /19. Always look for your block size and the interesting octet and you can find your answer every time.



My thoughts where the block size was 8 in the third octet. Therefore the prefix-length should have been 21.

Is the answer wrong or am I going mad? What am I missing/doing wrong? Many thanks

manav.g.garg

jambla85 wrote: »

I am slightly confused by a question I have come across.

By looking at the following output, which of the following commands would allow dynamic translations?
Router#show ip nat trans
Pro Inside global Inside local Outside local Outside global
--- 1.1.128.1 10.1.1.1 --- ---
--- 1.1.130.178 10.1.1.2 --- ---
--- 1.1.129.174 10.1.1.10 --- ---
--- 1.1.130.101 10.1.1.89 --- ---
--- 1.1.134.169 10.1.1.100 --- ---
--- 1.1.135.174 10.1.1.200 --- ---

a) ip nat inside source pool todd 1.1.128.1 1.1.135.254 prefix-length 1
b) ip nat pool todd 1.1.128.1 1.1.135.254 prefix-length 19
c) ip nat pool todd 1.1.128.1 1.1.135.254 prefix-length 18
d)ip nat pool todd 1.1.128.1 1.1.135.254 prefix-length 16

Answer
What we need to figure out for this question is only the inside global pool. Basically, we start at 1.1.128.1 and end at 1.1.135.174; our block size is 64 in the third octet, or /19. Always look for your block size and the interesting octet and you can find your answer every time.



My thoughts where the block size was 8 in the third octet. Therefore the prefix-length should have been 21.

Is the answer wrong or am I going mad? What am I missing/doing wrong? Many thanks

Yes the inside global range does fall in the block size of 8 but since /21 is not provided in the ans stick to the next best option . Therefore i think option b " ip nat pool todd 1.1.128.1 1.135.254 /19" would be correct