Superneting and IPARP

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Well today I was trying to locate a port associated with an IP address. when I did a "sh iparp" the address is not listed in the output.  I know the device is physically connected to one of the switches in the stack.  So I switched to our summit 250 stack and checked there.  the IP address came up but it resulted to 2:49.  Ok this is means its back on my 440 stack.  So I switched back to the 440 and then I realize none of IP address using X.X.21.X are showing in the list on the 440 stack but the 250 stack points it back to the main 440 stack.  

So now my question is what am I doing wrong.  I physically traced the cable back to the bottom switch of my 440 stack, which is were I knew was I just wanted to the port number for some notes I was making. 

We use a DHCP server using a mask of 255.255.254.0, or IP range of X.X.X.X/23 if your prefer.  What is proper way to get the stack to show me the port associated with the IP using the different 3rd octet (X.X.20.1 versus X.X.21.2) 

FYI We don't have an issue with network access on the x.x.21.x side of the house. 

I had nothing to do with our original vlan setup so I wonder if something is amiss there.
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Joe

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Posted 4 years ago

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Bill Stritzinger, Alum

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Joe,

Not that you are doing anything wrong at all.. without an x.x.21.x vlan configured on the switch you will not have an ARP table.  So if you look at the vlan list do you show a L3 interface on them? Do a "show vlan" and see if the IP addresses listed?

BIll
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Ben Parker

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So is the best practice in a case like this to create an L3 interface on all vlans and leave ipforwarding disabled so you can easily find the a port via an IP address,or is there a better way to find what port an ipaddress is on without creating all those ip addresses such as through IDM or something?

I guess simply put, what is the best way to find the port from the ip in XOS?
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Joe

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I was looking at the switch the other night over the weekend and I think the issue is the netmask used in the default vlan set up. I been trying to decide if I should tweak it or leave it.
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Bill Stritzinger, Alum

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Well the biggest difference is that if there is no IP (where switch is just layer 2) there will not be an ARP table.  In order to see the ARP table on specific vlans you would need a L3 interface configured.  The best way would be to enable identity manager and at least you could use the command "show identity-manager entries" and be able to see mac and IP bindings.
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Joe

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Thanks.  I will look into the identity manager, did not know about until your reply..
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Drew C., Community Manager

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You could also go back to the X250 stack and find the device's MAC address in the iparp table, similar to what you were doing before.  From there, go back to the 440 stack and do show fdb (mac_address).
That should tell you where the device is connected.
(Edited)
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Joe

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thanks for the info.  work like a charm.