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 Post subject: Getting host onto internet
PostPosted: Sun Mar 31, 2013 3:11 am 
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Posts: 4
Hello, all.

I'm just getting everything configured via GNS3. Wonderful program by the way.

Anyhow.

I have the Cloud set up. The loopback is tied to the cloud. 192.168.137.1

I set up a router which is named R1 - I set the IP on the FA0/0 to 192.168.137.2

I then setup a static route - ip route 0.0.0.0 0.0.0.0 192.168.137.1

I can ping out to 8.8.8.8 - Life is good!



----------

I then messed with the Virtual BOX, and got a XP host setup within GNS3.

I setup the fa0/1 interface with 10.0.0.1 255.255.255.0

And then XP Box with 10.0.0.3 255.255.255.0

I try to ping out to the internet and I'm not able to get out.

Is it because I don't have NAT enabled?

Please advise. Thanks.




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 Post subject: Re: Getting host onto internet
PostPosted: Sun Mar 31, 2013 9:49 am 
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Joined: Sun Sep 16, 2012 9:55 pm
Posts: 541
Location: England
I short yes... but you have two options. Basically the problem is the system that is behind the cloud doesn't know anything about your network on the other side of the Cisco router, this where you have two options...

1. Perform NAT on the Cisco router that is connected to the cloud to translate the source address
2. Add a route on the system behind the cloud so it knows how to get to the network on the other side of the Cisco router.

It's important to remember that a packet has to be able to find a path in both directions. I find it can help if you visualise the packet travelling and what it's going to be doing at each step.

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Daniel
Forum Moderator & Debian Package Maintainer for GNS3, Dynamips & VPCS.
Standalone DEB Packages are available from http://gns3.serverb.co.uk - To be updated!


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 Post subject: Re: Getting host onto internet
PostPosted: Sun Mar 31, 2013 12:59 pm 
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Joined: Sun Mar 31, 2013 3:02 am
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claydon_dan wrote:
I short yes... but you have two options. Basically the problem is the system that is behind the cloud doesn't know anything about your network on the other side of the Cisco router, this where you have two options...

1. Perform NAT on the Cisco router that is connected to the cloud to translate the source address
2. Add a route on the system behind the cloud so it knows how to get to the network on the other side of the Cisco router.

It's important to remember that a packet has to be able to find a path in both directions. I find it can help if you visualise the packet travelling and what it's going to be doing at each step.


Thanks for the response, Claydon_dan

Okay.

Regarding option 2. When I do a show ip route on the router it's able to see the 10.0.0.0 network. Shouldn't that router(R1) be able to route the packet to the default route?

Guess I'm just a little confused.


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 Post subject: Re: Getting host onto internet
PostPosted: Sun Mar 31, 2013 7:59 pm 
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Joined: Sun Sep 16, 2012 9:55 pm
Posts: 541
Location: England
lamplight wrote:
Regarding option 2. When I do a show ip route on the router it's able to see the 10.0.0.0 network. Shouldn't that router(R1) be able to route the packet to the default route?

I'm guessing your Internet Connection Sharing based on the gateway ip you posted earlier (192.168.137.1).

As an example I'll use a ping to 8.8.8.8
R1 will route the packet from your 10.0.0.0 network (e.g 10.0.0.2) to the default gateway 192.168.137.1 (but won't change the source address).
ICS will receive the packet and perform NAT on the source address, then route this packet its default gateway.
When the reply is received ICS will translate the destination address back to 10.0.0.2
It will then try and forward that packet by looking at the routing table(on that machine) where it will find that it doesn't know about 10.0.0.0 so will then discard the packet as 'Address Unreachable'

Again visualise it in your head... step by step, just because a packet can travel in one direction, it doesn't mean it will find a route back. As I said before imagine a car travelling along the road following the signposts. If when the car tries to come back the other way, there are no signposts it won't be able to reach its destination.

_________________
Daniel
Forum Moderator & Debian Package Maintainer for GNS3, Dynamips & VPCS.
Standalone DEB Packages are available from http://gns3.serverb.co.uk - To be updated!


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 Post subject: Re: Getting host onto internet
PostPosted: Mon Apr 01, 2013 1:35 pm 
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Joined: Sun Mar 31, 2013 3:02 am
Posts: 4
claydon_dan wrote:
lamplight wrote:
Regarding option 2. When I do a show ip route on the router it's able to see the 10.0.0.0 network. Shouldn't that router(R1) be able to route the packet to the default route?

I'm guessing your Internet Connection Sharing based on the gateway ip you posted earlier (192.168.137.1).

As an example I'll use a ping to 8.8.8.8
R1 will route the packet from your 10.0.0.0 network (e.g 10.0.0.2) to the default gateway 192.168.137.1 (but won't change the source address).
ICS will receive the packet and perform NAT on the source address, then route this packet its default gateway.
When the reply is received ICS will translate the destination address back to 10.0.0.2
It will then try and forward that packet by looking at the routing table(on that machine) where it will find that it doesn't know about 10.0.0.0 so will then discard the packet as 'Address Unreachable'

Again visualise it in your head... step by step, just because a packet can travel in one direction, it doesn't mean it will find a route back. As I said before imagine a car travelling along the road following the signposts. If when the car tries to come back the other way, there are no signposts it won't be able to reach its destination.


Thanks for the visualization. It makes much more sense now. However, what needs to be done to allow the packet to find its way home to the Host?

I'm guessing NAT

But I'm not very strong with NAT/ACL's as I haven't had much practice.

Thanks for the help!


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 Post subject: Re: Getting host onto internet
PostPosted: Mon Apr 01, 2013 9:28 pm 
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Joined: Sun Sep 16, 2012 9:55 pm
Posts: 541
Location: England
Rather than me trying to explain how to configure NAT/PAT I would take a look at this:Free CCNA Workbook - Configuring Port Address Translation

As well as the resource above using the IOS inline help can also prove very useful for seeing what options are available to you.

You will want to configure this on your R1 router.

_________________
Daniel
Forum Moderator & Debian Package Maintainer for GNS3, Dynamips & VPCS.
Standalone DEB Packages are available from http://gns3.serverb.co.uk - To be updated!


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 Post subject: Re: Getting host onto internet
PostPosted: Wed Apr 03, 2013 4:34 pm 
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Joined: Sun Mar 31, 2013 3:02 am
Posts: 4
claydon_dan wrote:
Rather than me trying to explain how to configure NAT/PAT I would take a look at this:Free CCNA Workbook - Configuring Port Address Translation

As well as the resource above using the IOS inline help can also prove very useful for seeing what options are available to you.

You will want to configure this on your R1 router.


Thanks for the link.

I have been busy lately. Been moving

Hopefully I can get this configured on Friday.

I'll let you know, Claydon_dan




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