DHCP client state if rebooted when local DHCPD server is offline?

[terrygalant.lists at fastest.cc]

Hi Greg

On Thu, Aug 14, 2014, at 10:30 AM, Gregory Sloop wrote:
> It seems clear that there's some problem with the DHCP server, [or perhaps VLAN's or network connectivity.]
> 
> How about a quick packet capture to be sure the DHCP server is actually seeing the requests. [I think this is the first, most important step.]
> -If it IS seeing them, then there's some configuration problem.
> -If it isn't, then figuring out what's preventing the communication from occurring, would be important. [Broadcast filtering, DHCP server and DHCP client on different VLANs without a DHCP helper/relay etc.]

Assuming that dhcping is a useful way to test, 

checking from my client

	dhcping -h XX:XX:XX:XX:XX:XX -s 10.16.10.1 -c 10.16.10.26
		Got answer from: 10.16.10.1

Watching on the server

	tcpdump -vvv -i eth1 -s 1500 port bootps or port bootpc
		tcpdump: listening on eth1, link-type EN10MB (Ethernet), capture size 1500 bytes
		11:31:52.432820 IP (tos 0x0, ttl 64, id 33227, offset 0, flags [DF], proto UDP (17), length 278)
		    tgdesktop.MYDOMAIN.net.bootpc > edgerouter.MYDOMAIN.net.bootps: [udp sum ok] BOOTP/DHCP, Request from XX:XX:XX:XX:XX:XX (oui Unknown), length 250, xid 0x9800ed53, Flags [none] (0x0000)
		          Client-IP tgdesktop.MYDOMAIN.net
		          Client-Ethernet-Address XX:XX:XX:XX:XX:XX (oui Unknown)
		          Vendor-rfc1048 Extensions
		            Magic Cookie 0x63825363
		            DHCP-Message Option 53, length 1: Request
		            Requested-IP Option 50, length 4: tgdesktop.MYDOMAIN.net
		            END Option 255, length 0
		11:31:52.433206 IP (tos 0x0, ttl 64, id 5840, offset 0, flags [DF], proto UDP (17), length 328)
		    edgerouter.MYDOMAIN.net.bootps > tgdesktop.MYDOMAIN.net.bootpc: [bad udp cksum 0x6fed -> 0x1b16!] BOOTP/DHCP, Reply, length 300, xid 0x9800ed53, Flags [none] (0x0000)
		          Client-IP tgdesktop.MYDOMAIN.net
		          Your-IP tgdesktop.MYDOMAIN.net
		          Client-Ethernet-Address XX:XX:XX:XX:XX:XX (oui Unknown)
		          Vendor-rfc1048 Extensions
		            Magic Cookie 0x63825363
		            DHCP-Message Option 53, length 1: ACK
		            Server-ID Option 54, length 4: edgerouter.MYDOMAIN.net
		            Lease-Time Option 51, length 4: 14400
		            Subnet-Mask Option 1, length 4: 255.255.252.0
		            Default-Gateway Option 3, length 4: edgerouter.MYDOMAIN.net
		            Domain-Name-Server Option 6, length 4: edgerouter.MYDOMAIN.net
		            Domain-Name Option 15, length 18: "MYDOMAIN.net"
		            END Option 255, length 0
		            PAD Option 0, length 0, occurs 6
		11:31:52.433580 IP (tos 0x0, ttl 64, id 33228, offset 0, flags [DF], proto UDP (17), length 272)
		    tgdesktop.MYDOMAIN.net.bootpc > edgerouter.MYDOMAIN.net.bootps: [udp sum ok] BOOTP/DHCP, Request from XX:XX:XX:XX:XX:XX (oui Unknown), length 244, xid 0x9800ed53, Flags [none] (0x0000)
		          Client-IP tgdesktop.MYDOMAIN.net
		          Client-Ethernet-Address XX:XX:XX:XX:XX:XX (oui Unknown)
		          Vendor-rfc1048 Extensions
		            Magic Cookie 0x63825363
		            DHCP-Message Option 53, length 1: Release
		            END Option 255, length 0

There's a "bad udp cksum" in there that doesn't look so good.  But the server IS getting the request it seems, and the client DOES get a reply.

Terry