Network Connectivity Problem on the 640-607...

[jsingh7]

Lisbon_Router <-->Gibralter_Router<-->TFTP_Server
192.168.15.0/20 192.168.15.0/20 192.168.15.62
| e0=192.168.15.8 255.255.255.255.192
| |
Host Default Gateway of
192.168.15.0/20 TFTP Server is
192.168.15.8

Question: A network administrator has installed a new router in the Lisbon office and is unable to backup the IOS image of the new router to the TFTP Server located in the Gibralter office. Given the network diagram, identify the source of the problem?

A) Incorrect default gateway of the TFTP Server
B) Incorrect subnet mask of the TFTP Server
C) Incorrect IP Address of the TFTP Server
D) Incorrect IP Address on e0 of the Gibralter Server
E) Incorrect subnet mask on the Lisbon Router

Now I thought the answer was A) because shouldn't the Default Gateway be 192.168.15.1? However, it states that the correct answer is E). How can the IP Address of the Default Gateway be the same as that of the Gibralter Server? Help!!!

 

[jeter]

lisbon and the gibralter routers have the same ip network
192.168.15.0/20

Whats up with the subnet on the tftp server? You have 255.255.255.255.192?

Is this the actual question and answers? “Reserve your right to think, for even to think wrongly is better than not to think at all”

Fisher CCNA,(CCNP-Routing)

 

[jsingh7]

Ooops... The Subnet Mask of the TFTP Server is 255.255.255.192... All other info. on the question is as it was... But you still haven't answered my questions...

 

[AZSKI]

I'm assuming the addresses shown on the Lisbon router are incomplete or incorrect somehow... The Lisbon LAN and the link (I assume serial connection) between the routers are all configured with the same subnet/host??? (192.168.15.0/20 is a host address)

The default gateway is not an issue. On Gibralter, e0 IP address is 192.168.15.8/20. The TFTP server connected to Gibralter e0 has IP address 192.168.15.62/26, default gateway 192.168.15.8. Default gateway is OK... there's no rule requiring the gateway to be xxx.xxx.xxx.1 So long as the router port IP address and default gateway IP address of the connected server (or host) match, you're good to go.

There is a specific problem with the Gibralter LAN, though.

The problem I see is that e0 IP address is 192.168.15.8 (192.168.15.0/20, host portion of address is 15.8, or 1111.00001000), yet the TFTP server is 192.168.15.62/26 (host portion of this address is .62, or 111110).

This results in an address mismatch on the Gibralter LAN, since the last 4 bits of the e0 address within the &quot;host&quot; portion of the address (255.255.240.0 is the /20 mask), but are within the &quot;network&quot; portion on the TFTP server (255.255.255.192, or /26). This results in the e0 and TFTP server addresses having different network #s: 192.168.0.0 on e0 and 192.168.15.0 on the TFTP server.

This does not address the repetiton of host addresses elswhere in the config as you've provided it. Maybe that should be something other than /20 (255.255.240.0)??? If the answer is &quot;E&quot;, something's wrong here.

 

[TechStudent]

Hi,

Let see if i understood this (this is just a theory)

Lisbon router:

S0: 192.168.15.0/20
E0: 192.168.15.0/20

Gibralter:
E0: 192.168.15.8/26
SO: 192.168.15.0/20
TFTP: 192.168.15.62/26

There's an address class wich i allways confuse, classless and classfull, one of them does not have mask information (i think it is the classfull) and the router assumes it has its default mask, there's other type called classless wich has mask info so you can use a class C address with a class B subnet mask and i think this is the issue here.

Address on Lisbon's Serial and gibralter serial matches (i think they are using it as a some kind of example network address instead of host

There you have a different subnet assigned to E0 at gibralter wich is necesary to route, you have to configure each interface in a different net/subnet in order to be routed.

Take a look at the supoussed interfaces at Lisbon, E0 and S0 are in the same net/subnet, it is not possible for the router to route from one interface to another into the same net/subnet.

This is my theory, hope it helps


Jose Paez

 

[TechStudent]

By the way,

About your question of tftp's server default gateway, think about it:

Lisbon and Gibralter are pretty far away, they has a serial connection to a wan, you have the tftp server locally where the gibralter router is, so it has to be connected to the e0 not to the routers serial interface, so when you configure a computer, you put the next hop as a gateway for it to look for a network it does not knows, i think the tftp server address has been mentioned only to realize the gibralter router's E0 subnet mask.

This question is a piece of work, the problem its not at the gibralter router, is was installed before and it was functioning, the new kid on the block its the Lisbon router wich has the same net/subnet config for the two interfaces.

No routing can occur betwen Lisbon's E0 & S0, pretty good exam problem, slippery don't you think?

Bye


Jose Paez

 

[Guest_imported]

to start off with was it me or all my subneting questions were all /26? magic number is 16.

Anyhow if I remember right what was goofy was the subnets on in this question. I did notice on my test that the Lisbon router had an hostnumber of .16 which would land it on the network number not a valid host address.

I think I chose the last answer that the mask on the lisbon router was wrong

 

[Guest_imported]

to start off with was it me or all my subneting questions were all /26? magic number is 16.

Anyhow if I remember right what was goofy was the subnets on in this question. I did notice on my test that the Lisbon router had an hostnumber of .16 which would land it on the network number not a valid host address.

I think I chose the last answer that the mask on the lisbon router was wrong