An AP’s radio interface performs different functions than an access (non-trunked) port on a switch.A few reasons why Wi-Fi DHCP is a little different follow: There are a few more potential gotchas on the wireless segment, though. For this, the router uses the interface (or subinterface) IP address that matches the client’s VLAN.įor wireless clients, when you understand the above process, DHCP is not terribly complex. When a router forwards the frame across the IP network, the router must include a relay IP address so that the DHCP server can send the DHCP offer back to the proper relay device. Remember that the original client doesn’t yet have an IP address, so there is no source IP address in the DHCP discovery. However, the router does something interesting. In the case of DHCP, the router will forward the DHCP discovery and request as unicast frames to one or more pre-configured DHCP servers. Typically, this is accomplished by configuring an IP Helper Address on the router, which is just a way of telling the router to relay certain broadcast UDP frames (like DHCP) to a specific IP destination. However, if the DHCP server is not on the local subnet, a router must be configured to forward the DHCP discovery. If there’s a DHCP server on the local Layer 2 domain, it will reply and everyone will be happy. When the client connects, it does the usual DHCP exchange by sending a broadcast DHCP discovery frame to find a DHCP server. In a typical client connection to a wired Ethernet port, the client will be a member of a VLAN based on the switch port configuration. In this article, I want to focus on understanding a few ways in which your wireless infrastructure participates in the client’s process of obtaining a DHCP address. To give you a nudge on your journey, let’s talk about Dynamic Host Configuration Protocol (DHCP) for wireless clients.ĭynamic Host Configuration Protocol (DHCP) is one of those oft-overlooked topics that you must understand for initial wireless configuration and connectivity troubleshooting.
Understanding wired design topics is pretty fundamental to installing or managing any network, so it really should be on our priority list to spruce up those skills. For us wireless folks that aren’t stellar routing and switching guys, one of the most daunting network tasks is integrating our WLAN infrastructure with the existing wired infrastructure and its services.
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