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Routing table for an host (IPv4)

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#1 tigerjack89

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Posted 24 January 2014 - 13:33

Hy guys!!
First question here and I'm a newbie  :)
During my Computer Networking exam, I was asked to find a simple rounting table both for the R4 router and the only host in this image
 
But, while the routing table for R4 is quite straightforward to me, the one for the host raised many doubts.
I tried something like that.
 
    IP dest              Mask                  Next Router          Out Interface
    194.17.21.0     255.255.255.0    //                            ??
     0.0.0.0             0.0.0.0               194.17.21.14          ??
 
Btw, I'm not sure if it's the right way to approach and what is the right Out interface.
Is it the same of the host IP (i.e. 194.17.21.16)? If yes, does it mean that the host out interface is the same of it's IP address? In other words, an host have the same IP address of its out interface? An host have the same IP address of its network device?
 
Thanks in advance :)


Best Answer +BudMan , 26 January 2014 - 18:06

From the drawing the host only has 1 interface, so yeah that would be the out interface ;) Depending on the OS the route could be shown via the IP on the interface, or could be shown as the actual interface.

What OS is on the host would be the only way to be sure on the proper syntax of creating the route on the host.

So in that table can you see the routing tables of the routers shown? Is there any mention of routing protocol between them sharing their routes? If not its hard to say the proper route out. Which way does R2 route to network host is connected too, you would like to assume least hops - but you can not be sure without some more details.

If you were routing to the 192.16.7 network via r5, what would you be talking to in that network. A host, what routing table does it have? Because if it only has a default route out R3, you most likely run into a asynchronous routing problem with hosts talking to 192.16.7 from 194.17.21

As typical these sorts of questions/exams have little to do with a real life example.

Curious to see what the documented correct answer it - its always fun to ask how they got there with what is normally a lack of actual information given.

Then you have to love the just pulling networks out of their ass to use in diagrams, 111.0.0.0/10 owned by china mobile China Mobile Communications Corporation. APNIC, and then a Sweden TV network it seems RIPE..

Come on how hard is it to come up with a realistic diagram and question that reflects what might really happen in the realworld ;) Go to the full post



#2 OP tigerjack89

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Posted 26 January 2014 - 10:56

Any ideas on this? :(



#3 n_K

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Posted 26 January 2014 - 11:00

I have no idea how that image translates, are the circles showing the networks attached or are they switches/hubs or what?



#4 OP tigerjack89

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Posted 26 January 2014 - 11:03

I have no idea how that image translates, are the circles showing the networks attached or are they switches/hubs or what?

The circles represent networks, while the boxes stand for routers :)



#5 The_Decryptor

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Posted 26 January 2014 - 11:17

The host can see 2 routers, R4 and R5, it'd presumably route traffic through R4 due to the lower overall hops to get out to internet.

If it wants to send data to 192.16.7/24 it'd send data through R5, otherwise it'd send it through R4.

Edit: I think at least, haven't done routing since like 2011.

#6 OP tigerjack89

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Posted 26 January 2014 - 17:13

The host can see 2 routers, R4 and R5, it'd presumably route traffic through R4 due to the lower overall hops to get out to internet.

If it wants to send data to 192.16.7/24 it'd send data through R5, otherwise it'd send it through R4.

Edit: I think at least, haven't done routing since like 2011.

Thanks for the support :)
Yes, I think you're right and I should modify the table.
Btw, what do you think about the output interface (and the related questions in the OP) ?



#7 +BudMan

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Posted 26 January 2014 - 18:06   Best Answer

From the drawing the host only has 1 interface, so yeah that would be the out interface ;) Depending on the OS the route could be shown via the IP on the interface, or could be shown as the actual interface.

What OS is on the host would be the only way to be sure on the proper syntax of creating the route on the host.

So in that table can you see the routing tables of the routers shown? Is there any mention of routing protocol between them sharing their routes? If not its hard to say the proper route out. Which way does R2 route to network host is connected too, you would like to assume least hops - but you can not be sure without some more details.

If you were routing to the 192.16.7 network via r5, what would you be talking to in that network. A host, what routing table does it have? Because if it only has a default route out R3, you most likely run into a asynchronous routing problem with hosts talking to 192.16.7 from 194.17.21

As typical these sorts of questions/exams have little to do with a real life example.

Curious to see what the documented correct answer it - its always fun to ask how they got there with what is normally a lack of actual information given.

Then you have to love the just pulling networks out of their ass to use in diagrams, 111.0.0.0/10 owned by china mobile China Mobile Communications Corporation. APNIC, and then a Sweden TV network it seems RIPE..

Come on how hard is it to come up with a realistic diagram and question that reflects what might really happen in the realworld ;)

#8 OP tigerjack89

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Posted 26 January 2014 - 19:32

Lot of interesting stuffs here; don't know if I can be able to understand all of them tbh, but i get the points (I think :D ).
So, taking a (partial) real word example: suppose I have two network device, a wifi card and an ethernet card.
When I connect to the Internet via the ethernet card, my machine IP address is the same of the card?
What happens if I use both card to connect to the internet? Do I have two external IP address?

 

Thanks as always :)



#9 +BudMan

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Posted 26 January 2014 - 19:46

Lets say you had wifi and wired -- Why would you connect to both at the same time would be my first question. Are they on the same network. For example my wireless is 192.168.2.0/24 while my wired would be 192.168.1.0/24

As to which one you would use to get to the internet - which one has the best metric?

Windows by default would use automatic metric to figure out which interface to use.. This metric is based upon a few different attribute of the connection. Speed being one of them - so wired would always be used you would have to assume over wireless if both have default gateways.

As to having 2 external address - external to where? More than likely your machine would be behind a nat to get to the internet anyway.. So even if you bounced off using wired for one connection and wireless for another connection to the internet you would still only have 1 address ;)

Multi homing a machine with more than 1 interface in the same network is normally not good practice and has its own issues btw.

So you saying wifi and wired at the same time is not really a valid real world example either - unless your talking some user at home that doesn't know any better and what to discuss why having this sort of connection could cause him issues ;) Then it would be a good real world example.. Look around the net you find lots and lots of FUD, where people suggest that user bridge his wired and wireless, or both of his wired intefaces for FASTER internet ;)