Is this a trick eigrp question from Boson?

phoeneous

See attached image for a question from Boson's ICND2 practice test. Did they just use process of elimination to get to that answer or is it a trick question? The explanation confuses me...

miller811

The explanation is accurate.
The command issued, says show me routes that are learned via EIGRP.
as stated the 10.25.67.33 is an ip address which is part of the subnet
10.25.67.32, that is why A is wrong and C is right

b is an IP address, not a subnet so it is wrong.
D is the subnet between the routers, but it is a connected route (on router b), not a route learned from EIGRP
E is also a connected route (on router b), not a route learned via EIGRP.

phoeneous

miller811 wrote: »

The explanation is accurate.
The command issued, says show me routes that are learned via EIGRP.
as stated the 10.25.67.33 is an ip address which is part of the subnet
10.25.67.32, that is why A is wrong and C is right

b is an IP address, not a subnet so it is wrong.
D is the subnet between the routers, but it is a connected route (on router b), not a route learned from EIGRP
E is also a connected route (on router b), not a route learned via EIGRP.

Well duh. So you have to subnet it first to figure out the ranges. 10.25.67.0, 10.25.67.32, etc...

So the sh ip route eigrp command only shows subnets and not ip's?

M4verick

Yeah, it would show routes learned via EIGRP, which would be by the subnet, not the individual IP address. The easiest way to remember that is that the routes refer to the direction of that entire network, not just the one IP address.

billscott92787

M4verick wrote: »

Yeah, it would show routes learned via EIGRP, which would be by the subnet, not the individual IP address. The easiest way to remember that is that the routes refer to the direction of that entire network, not just the one IP address.

This is an excellent explanation by M4verick. When you look at the routes in the routing table (show ip route) it is going to show you just as M4verick said, the route to that particular network or subnet.


Think of it this way, this goes back to the fact that when a packet comes in, it is compared to the routing table. That packet is then forwarded out to the next hop, with the longest match. Say that a packet comes in with the destination IP: 10.25.67.33 /27

Destination IP: 10.25.67.33 /27

00001010.00011001.01000011.00100001




10.25.67.32 /27 or

00001010.00011001.01000011.00100000


As you can see 31 bits match... Hope this doesn't confuse you just trying to help explain what it really boils down to.

phoeneous

billscott92787 wrote: »

This is an excellent explanation by M4verick. When you look at the routes in the routing table (show ip route) it is going to show you just as M4verick said, the route to that particular network or subnet.


Think of it this way, this goes back to the fact that when a packet comes in, it is compared to the routing table. That packet is then forwarded out to the next hop, with the longest match. Say that a packet comes in with the destination IP: 10.25.67.33 /27

Destination IP: 10.25.67.33 /27

00001010.00011001.01000011.00100001




10.25.67.32 /27 or

00001010.00011001.01000011.00100000


As you can see 31 bits match... Hope this doesn't confuse you just trying to help explain what it really boils down to.

I understand routing. Once I realized its really just a subnetting question, I answered it in about 10 seconds. I thought that there was some underlying eigrp concept that I was missing. I feel dumb for not thinking to subnet it first.

miller811

phoeneous wrote: »

I understand routing. Once I realized its really just a subnetting question, I answered it in about 10 seconds. I thought that there was some underlying eigrp concept that I was missing. I feel dumb for not thinking to subnet it first.

Don't feel that way, it was testing all of your skills.
They wrote the question that way to make you think.

It should reinforce that while in the testing center take time to really identify everything before answering the question.