Device Tracking with SVI

[BlueyVIII]

I'm troubleshooting a Windows 10 DHCP Issue which I think is related to IP Device Tracking. I think I can solve the problem with the command below :-

ip device tracking probe auto-source fallback 0.0.0.1 255.255.255.0

However, I can't find any more info about how this command actually works? If I implement this command, will the switch use the IP address configured on the SVI as the source address for the IPDT ARP's, or will it use the IP Addresses configured in the command?

I've read differing explanations for how the command works but can't find anything official.

If the impacted subnet is 192.168.100.0/25 and the SVI (VLAN10) address is 192.168.100.1/25 will IP device tracking use 192.168.100.1 as the source address?

I think it could be the 'fallback' element of the command that's confusing. Is this only used if the SVI doesn't have an IP Address?? 

[Jon Marshall]

As I understand it it will use the SVI IP address if there is a L3 SVI with an IP but if there is no SVI then it will generate an IP using that mask and host bits. 

See this link (which you may already have seen) - 

https://www.cisco.com/c/en/us/support/docs/ip/address-resolution-protocol-arp/118630-technote-ipdt-00.html#anc8

Jon

[Reza Sharifi]

Have a look at this post for more info, and a long discussion when it comes to using this command. 

Also, we deployed this command recently, and it was causing packet loss and multicast problems on the switch. Once removed, no more packet loss. so, be careful with this command.

https://community.cisco.com/t5/network-access-control/ip-device-tracking/td-p/3710912

HTH

[BlueyVIII]

Thanks - It was that post that actually led me to creating my post as I thought it was the right way to go, but wasn't clear on how the command actually works.

All of the switches I'll be configuring this on will have L3 SVI's configured, so I was wondering :-

1. Can I omit the 'fallback' part of the command as won't this be unnecessary??

2. If the 'fallback' IP Addresses is mandated, should I remove the chosen IP Address from the VLAN DHCP Pool to prevent that IP Address from becoming a duplicate an making things worse?