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next hop vs interface routing

Posted on 2010-11-11
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Last Modified: 2012-05-10

Hi,

I inherited a strange IP setup and I'm not sure how to solve this routing issue.

I have a few devices with IP addresses in the 3.0 subnet. There is no router in between to route to the 3.0 subnet.  I also have a 1.0 and a 4.0 subnet.

If I want to ping those devices(3.x) from a 1.0 machine I go:
route add 192.168.3.0 mask 255.255.255.0 192.168.1.103 where 103 is the ip of the workstation.

Now I need to ping those devices from a different subnet. How do I do that?

I need to ping from subnet 2.0. This subnet has the gateway 192.168.2.1. The other interface of the router is 192.168.1.30. That's how subnet 2.0 reaches resources (files, internet). Is this considered next hop routing?

How can I ping a device in the 3.0 subnet from 192.168.2.87 for example?

Any help would be appreciated.

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Question by:foresthome
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Trackhappy earned 250 total points
ID: 34117558
If you are saying that the .1, and .3 are on the same switch and they can talk to each otehr, I am not sure how it is working. Either the subnet has been broadened, or one has a secondary address on the interface. Maybe there is something I can learn here.

Can you draw a picture to show us more clearly what is where and what is configured. Check the advanced tab for secondary ip addresses, maybe post the results of ipconfig /all and route print commands on both the .1 and the .3 machines.
The answer might be to use vlans and use the router to route them, or simply use a broader subnet or maybe eliminate the different valns if they are really not needed.
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Expert Comment

by:jenili
ID: 34122875
Hi,

Paste your network design to understand the scenario.

Apply this command for intervlan communication

# ip routing
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by:giltjr
giltjr earned 250 total points
ID: 34123113
In some instances a switch that is VLAN aware will do a proxy arp for a IP address that is not on the same VLAN/IP Subnet as the requesting host.

So after you issue the command:

route add 192.168.3.0 mask 255.255.255.0 192.168.1.103

When you ping a host, say 192.168.3.22, 192.168.1.103 will send out a arp requst for 192.168.3.22.  The switch may respond with the MAC address for 192.168.3.22.  Then 192.168.1.103 will send the ICMP to 192.168.3.22 with its' MAC address.  The switch knows what port that MAC is on and forwards it.  That host (192.168.3.22) will respond normally.

I know that this works with L3 switches like a Cisco 6500 series with a MFSC card.

What type of switch do you have?

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Author Comment

by:foresthome
ID: 34123845

Thank you for your responses.

I have 2900 switches in the network and a 3550 between subnet 1.0 and 2.0. I see that those 3.0 subnet devices have a gateway of 192.168.1.1.



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Expert Comment

by:giltjr
ID: 34123990
O.K., 3550's can do IntraVLAN routing.

I don't know for sure what is exactly occuring, but my guess is that since the 3550 knows how to get to all of the subnets, it is doing proxy arp.

Description of what proxy arp is and how it works:

    http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080094adb.shtml

What I would suggest is you setup the 3550 so it can do IntraVLAN routing for all of your IP Subnets/VLANs:

http://www.cisco.com/en/US/tech/tk389/tk815/technologies_configuration_example09186a008015f17a.shtml
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