How to Configure L3 Switch as DHCP Server for Both LAN and Wireless

[phuocntlk135]

Hi Community,

I’m currently working on a network design where I want the Layer 3 Switch (Cisco) to handle DHCP for both wired (LAN) clients and wireless clients (via Access Point). Please see the attached topology diagram for reference.

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Network Topology Summary:

• WLAN Controller: IP: 192.168.1.100/24 (VLAN 1) - WLC 9800-CL deploy on vmware workstation. Use my own laptop to run WLC

• Cisco L3 Switch: Connects to:

  • Gi1 to WLAN Controller

  • F0/1 to Aruba L2 switch

• Aruba L2 Switch:

  • Port 1/2 connects to Access Point

  • Port 1/24 uplinks to Cisco L3

• VLANs in Use:

  • VLAN 1: 192.168.1.0/24 (Management)

  • VLAN 10: 192.168.10.0/24 (CAPWAP)

  • VLAN 20: 192.168.20.0/24 (Wireless Users)

  • VLAN 30: 192.168.30.0/24 (Wireless Guest)

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Goal:

• Use the Cisco L3 switch as a DHCP server for:

  • All LAN clients (wired, connected to VLANs 10, 20, 30, etc.)

  • Wireless clients (connected via Access Point on VLAN 20 and VLAN 30)

• Clients should receive IP from the correct DHCP pool and access the Internet via L3 switch routing.

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Questions:

1. Can I configure DHCP pools directly on the Cisco L3 switch for VLANs 10, 20, and 30 and serve both LAN and wireless clients from there?

2. Do I need to configure DHCP relay (ip helper-address) on the wireless side, or is it not necessary if everything is routed locally via the L3 switch?

3. How should I trunk/tag the ports between:

   • WLAN Controller ↔ L3 switch

   • L3 switch ↔ L2 switch (Aruba)

   • L2 switch ↔ Access Point

4. Do I need to configure VLAN interfaces (SVIs) for all VLANs on the L3 switch and assign the correct DHCP pools with default-gateway pointing to the SVI?

5. Any best practices to ensure clients get IPs and can access internet across both wired and wireless?

[srimal99]

Questions:

1. Can I configure DHCP pools directly on the Cisco L3 switch for VLANs 10, 20, and 30 and serve both LAN and wireless clients from there? Yes you can but the question is are you creating multiple ssids ? if you not you can use one vlan and  dhcp pool for wireless clients l and a  separate dhcp pool for lan client

2. Do I need to configure DHCP relay (ip helper-address) on the wireless side, or is it not necessary if everything is routed locally via the L3 switch?
   9800 dhcp config step are as follows, you need helper address on L3 switch dhcp as dhcp work as broadcast in lan network.
   https://wifininjas.net/2019/08/06/wn-blog-007-c9800-wlc-internal-dhcp-server-config/

3. How should I trunk/tag the ports between:

• WLAN Controller ↔ L3 switch  =  trunk  

• L3 switch ↔ L2 switch (Aruba)  = trunk ( all traffic need to allow via firewall as the exit point for internet)

• L2 switch ↔ Access Point = access vlan assigned to SSID 

1. Do I need to configure VLAN interfaces (SVIs) for all VLANs on the L3 switch and assign the correct DHCP pools with default-gateway pointing to the SVI?You need configure and assigned default gateway pointing to exit point.(Specifies the IP address of the default router for a DHCP client.)

2. Any best practices to ensure clients get IPs and can access internet across both wired and wireless?https://www.cisco.com/c/en/us/td/docs/wireless/controller/9800/technical-reference/c9800-best-practices.html
   

[phuocntlk135]

I creating multiple ssids at least 4 SSIDS

[phuocntlk135]

I creating multiple ssids at least 4 SSIDS. On switch L3 do i have to config option 43?

[srimal99]

You need to configure dhcp 43 for ap.

[phuocntlk135]

Can you show me how to config that

[srimal99]

https://www.cisco.com/c/en/us/support/docs/wireless-mobility/wireless-lan-wlan/97066-dhcp-option-43-00.html

above link give cli and gui configuration.