Show arp differs from IPDT

[StefanoFereri]

Hi,

device with IP address 192.168.0.1 is connected to a Catalyst 2960. When I ping to that device and do a show ip device tracking all command, this IP address is listed as expected (state: active: source: ARP). But when I do a show arp, this IP address is not listed. Any idea?

Thanks and regards,

Stefano

[Georg Pauwen]

Hello,

as far as I recall, the ARP cache of the switch would only show the ARP entries (and IP address mappings) for the IP addresses from the same subnet as the management IP address.

Or is the 2960 configured for IP Routing ?

[StefanoFereri]

Hi Georg,

it's indeed configured for IP routing. Due to this I can see IP addresses in different Vlans, with both commands. But I would expect that "show arp" is similar with "show ip device tracking all", or at least a subset.

Thanks
Stefano

[Georg Pauwen]

Hello,

that is correct, with 'ip routing' enabled, you should see all ARP mappings...

What does 'show ip arp' render ?

[Leo Laohoo]

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@StefanoFereri wrote:

device with IP address 192.168.0.1 is connected to a Catalyst 2960. When I ping to that device and do a show ip device tracking all command, this IP address is listed as expected (state: active: source: ARP). But when I do a show arp, this IP address is not listed. Any idea?

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IPDT and the mapping of IP address to MAC address via ARP are two different things.  

If the 2960 is doing nothing but Layer 2 only, "sh ip arp <MAC ADDRESS>" will result in a blank screen all the time because the switch does not understand IP address.  

IPDT was developed to circumvent this.