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iPXE ignoring DHCP ACKs
2011-05-12, 01:15
Post: #1
iPXE ignoring DHCP ACKs
I found iPXE because I needed an PXE client that supported vlan tagging. I've been using it successfully for months, but just recently it stopped having successful DHCP exchanges. I did a Wireshark capture of the DHCP exchange between the client and the DHCP server (which also serves out the pxelinux.0 later) and there is a full DHCP exchange, but there are a ton of repeated packets on the part of the diskless client. He sends around 10 DHCP discovers before he realizes that he's been getting DHCP offers, and he sends another 10 DHCP requests, receiving DHCP ACKs all the while. The problem is, the DHCP request in iPXE eventually times out. I guess the client is just ignoring the ACKs that I'm seeing it receive (I'm mirroring its port on its switch, which is how I'm able to monitor the exchange).

I'm not a complete expert on DHCP, is there some sort of timeout for each request, where if he doesn't receive an OFFER after his DISCOVER he sends another DISCOVER, ignoring any OFFERs that eventually come in?

I'm just really trying to figure out why none of the ACKs I clearly see him receive are taking, and I'm thinking maybe the ACKs are taking too long? The DHCP server works just fine for some other hardware I have (not using iPXE, just built-in Intel PXE).

Is there some way I can do a DHCP in verbose mode or something to get more information about how iPXE is processing the DHCP it gets?

I did a Wireshark capture of an Intel PXE boot loader that supports VLAN tagging and compared the packets with iPXE, and I noticed that there were different DHCP options set, such the Broadcast flag being set to Unicast on iPXE.
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iPXE ignoring DHCP ACKs - electronsrock - 2011-05-12 01:15

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