dhcp relay config location in c9800

[Leftz]

Hi, In c9800 wlc, looks like there are two sites for configuring dhcp relay. One is at Vlan SVI---> Advanced, second is at Policy ----> Advanced ----> DHCP. What is difference between the two location for configuring dhcp relay? I think the final result is same, the difference might be for different different range. Do you think so? Thanks

[Rasika Nayanajith]

In 9800, it is not recommended to configure 9800 as a DHCP relay. See below 9800 Best Practices document (DHCP Bridging & DHCP Relay section)

https://www.cisco.com/c/en/us/products/collateral/wireless/catalyst-9800-series-wireless-controllers/guide-c07-743627.html#Networkcontrollersettings 

Unless mDNS gateway use case, we are not defining any SVI on 9800 itself for wireless users (only wireless management SVI and out of band management). Therefore vlan SVI  DHCP won't come into a picture in most of the scenarios.

A configuration option is there under Policy -> Advanced section as well. Usually, you can tick "IPv4 DHCP Required" without specifying any DHCP server address there.

I would think policy configuration overwrite general interface configs if you configure at both locations (not 100% sure though)

HTH

Rasika

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[Leftz]

Thank you for your reply. 

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A configuration option is there under Policy -> Advanced section as well. Usually, you can tick "IPv4 DHCP Required" without specifying any DHCP server address there,

If doing like this, one dhcp server and users have to be at the same subnet, otherwise, we still have to use dhcp relay, right?

[Rasika Nayanajith]

If doing like this, one dhcp server and users have to be at the same subnet, otherwise, we still have to use dhcp relay, right?

On your upstream switch, you configure dhcp relay, not on your 9800. Most of the cases, 9800 just got management interfaces and no other SVI with IP address on client subnets. So best not to configure 9800 as dhcp relay-agent

HTH

Rasika

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