This is a series of packet dumps to show DHCP exchanges through a Wireless link. The link is composed of a Netgear MR814 Access Point and a Linksys WET-11 operating in infrastructure mode.
The DHCP Servers are those located in the Netgear Access Point, the one in a Linksys BEFSR41 Cable/DSL Router/Switch (Not wireless) and the isc.org DHCP server installed under Debian 8.0 on a 486 PC. Both the Linksys BEFSR41 and the isc.org DHCP servers are connected to the Access Point. The isc.org DHCP server was configured to the IP addresses in use.
The DHCP client is a laptop running Win 98. The Laptop is connected via it's docking station Ethernet port to the Ethernet port of the WET-11. The DHCP request was initiated by releasing then renewing in the winipcfg.exe dialog box. The packet exchanges were recorded twice, once from the AP end and once from the WET-11 end. In all cases the Laptop initiated the DHCP request. Because the packet dumps were recorded at two different times, sequence numbers will differ in packets shown from the AP end and the WET-11 end. The intent is to show the differences in the server replies to determine why the DHCP is not successful using the isc.org DHCP server through the link.The packets were recorded using a Power Mac 6500/225, Mac OS 9.1, Etherpeek 3.5. The names near the Ethernet and IP addresses are from Etherpeek's name table, which allows a more human readable packet display. Other annotations are built-into the packet display.
The Netgear MR814 Firmware Version is 4.09, Aug 23 2002
The Linksys WET-11 Firmware Version is 1.32
The Linksys BEFSR41 Firmware Version is 1.40.2, Oct 23, 2001
The isc.org DHCP server is Internet Software Consortium DHCP Server 2.0pl5.
The first packet recorded from the DHCP Client (Laptop) is a DHCP request. Note the hardware source address of the Laptop in the Ethernet Header, the Client Address field and the Client Identifier field.
The WET-11 transmitted the packet to the AP. Here it is on the Access Point side. Note the hardware source address in the Ethernet Header is now that of the WET-11, but that the Client Hardware address and Client Identifier fields still contain the hardware address of the Laptop.
The DHCP hosts received the above request packet. Each then generated a DHCP Reply.
The Netgear MR814 DHCP reply, observed at the Access Point.
The Netgear MR814 DHCP reply, observed at the WET-11.
The Linksys BEFSR41 DHCP reply, observed at the Access Point.
The Linksys BEFSR41 DHCP reply, observed at the WET-11.
Note that both the Netgear MR814 AP and the Linksys BEFSR41 DHCP servers replied with an Ethernet broadcast.
The isc.org DHCP reply, observed at the Access Point. No DHCP reply from the isc.org server was observed at the WET-11 end.
Note that the isc.org Server reply destination was the hardware address of the client, which must have come either from the Client Address field or from the Client Identifier field of the DHCP request packet, since the DHCP request that the isc.org server received had the WET-11 hardware address in the Ethernet Header.
The DHCP replies from the Netgear MR814 and the Linksys BEFSR41 were received at the DHCP client because they were sent as broadcasts. The DHCP reply from the isc.org DHCP server was sent to the hardware address of the client, but did not make it to the client through the Access Point/WET-11 link because the client hardware address was unknown to the Access Point.
B. Matson, June 8, 2003, Sebastopol, CA.