topic Re: DHCP server not working for iPXE in ExtremeSwitching (EXOS/Switch Engine)

DHCP server not working for iPXE

excessive — Wed, 13 Jan 2021 17:42:51 GMT

The switch is BlackDiamond X8.
I’ve set dhcp server for our lab VLAN that I’m using for testing. The pool range and everything else works as intended.
I’ve configured options 66 and 67 to FOG server machine and that’s where it breaks. I’m getting:

Filename: undionly.kpxe
Could not start download: Operation not supported (http://ipxe.org/3c092003)

I can confirm that when using separate isc-dhcp server there’s no problem. But I’d like to utilize our switch.

Here’s snippet of my configuration:

VLAN "XXX_TEST":
DHCP Address Range : 192.168.xx.xx->192.168.xx.xx
Netlogin Lease Timer : Not configured (Default = 10 seconds)
DHCP Lease Timer : 86400 seconds
Default Gateway : 192.168.xx.xx
Primary DNS Server : xx.xx.xx.xx
DHCP Option Code 66 : ipaddress 192.168.xx.xx
DHCP Option Code 67 : string "undionly.kpxe"
Ports DHCP Enabled : 1:21

Re: DHCP server not working for iPXE

StephanH — Wed, 13 Jan 2021 19:46:34 GMT

Hello,

do I understand correctly that the message:

Filename: undionly.kpxe
Could not start download: Operation not supported (http://ipxe.org/3c092003

is from you DHCP client?

Re: DHCP server not working for iPXE

excessive — Wed, 13 Jan 2021 19:51:09 GMT

Greetings, Stephan.
Yes, this is from my DHCP client (a workstation). It receives IP from the allocated pool then I get the quoted message.

Re: DHCP server not working for iPXE

StephanH — Wed, 13 Jan 2021 19:57:23 GMT

The easiest way to narrow down this is to do a wiresharktrace on you client (or on an mirror port on the swicht) to gather the DHCP-Messages. If you see the messages you can check if the values in the options are correct. If you can do the same while using you ISC you can compare the dhcp messages in both situations (= DHCP on ISC and DHCP on XOS).

I can’t see an error in your dhcp config directly. Therefore I assume something in the options is different.

Re: DHCP server not working for iPXE

excessive — Wed, 13 Jan 2021 20:17:41 GMT

Thanks for the advice! Guess I’ll have to level up my wireshark skills.

Re: DHCP server not working for iPXE

StephanH — Wed, 13 Jan 2021 20:29:30 GMT

Wireshark is not difficult here. Just enter "bootp" in the displayfilter line. Then you will only see the DHCP messages. The DHCP options are displayed in plain text.

Re: DHCP server not working for iPXE

excessive — Wed, 13 Jan 2021 21:53:34 GMT

Managed to capture some frames.
On the working scenario I have DISCOVER and OFFER packets passing.
Here’s some output:

Frame 475: 342 bytes on wire (2736 bits), 342 bytes captured (2736 bits) on interface \Device\NPF_{4C63F991-A548-48B3-A772-5278B943AE7F}, id 0
Ethernet II, Src: e6:95:01:b5:0a:4e (e6:95:01:b5:0a:4e), Dst: Broadcast (ff:ff:ff:ff:ff:ff)
Internet Protocol Version 4, Src: 192.168.230.51, Dst: 255.255.255.255
User Datagram Protocol, Src Port: 67, Dst Port: 68
Dynamic Host Configuration Protocol (Offer)
    Message type: Boot Reply (2)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0x9f77d344
    Seconds elapsed: 10
    Bootp flags: 0x8000, Broadcast flag (Broadcast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 192.168.230.170
    Next server IP address: 192.168.230.51
    Relay agent IP address: 0.0.0.0
    Client MAC address: 82:5d:c6:8a:7e:48 (82:5d:c6:8a:7e:48)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name: undionly.kpxe
    Magic cookie: DHCP
    Option: (53) DHCP Message Type (Offer)
    Option: (54) DHCP Server Identifier (192.168.230.51)
    Option: (51) IP Address Lease Time
    Option: (1) Subnet Mask (255.255.255.0)
    Option: (3) Router
    Option: (6) Domain Name Server
    Option: (15) Domain Name
    Option: (255) End
    Padding: 00000000000000000000000000000000

And here having the switch as DHCP I can see only two DISCOVER packets and one Request to which there seems to be no response at all.

Frame 370: 449 bytes on wire (3592 bits), 449 bytes captured (3592 bits) on interface \Device\NPF_{4C63F991-A548-48B3-A772-5278B943AE7F}, id 0
Ethernet II, Src: 82:5d:c6:8a:7e:48 (82:5d:c6:8a:7e:48), Dst: Broadcast (ff:ff:ff:ff:ff:ff)
Internet Protocol Version 4, Src: 0.0.0.0, Dst: 255.255.255.255
User Datagram Protocol, Src Port: 68, Dst Port: 67
Dynamic Host Configuration Protocol (Request)
    Message type: Boot Request (1)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0xa41b0d65
    Seconds elapsed: 14
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 0.0.0.0
    Next server IP address: 0.0.0.0
    Relay agent IP address: 0.0.0.0
    Client MAC address: 82:5d:c6:8a:7e:48 (82:5d:c6:8a:7e:48)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (53) DHCP Message Type (Request)
    Option: (57) Maximum DHCP Message Size
    Option: (93) Client System Architecture
    Option: (94) Client Network Device Interface
    Option: (60) Vendor class identifier
    Option: (77) User Class Information
    Option: (55) Parameter Request List
    Option: (175) Etherboot
    Option: (61) Client identifier
    Option: (97) UUID/GUID-based Client Identifier
    Option: (54) DHCP Server Identifier (192.168.230.253)
    Option: (50) Requested IP Address (192.168.230.200)
    Option: (255) End

Let me know if this helps or I should provide more data.

Re: DHCP server not working for iPXE

StephanH — Wed, 13 Jan 2021 22:03:09 GMT

Hello,

in your first post you wrote:

I’ve set dhcp server for our lab VLAN that I’m using for testing. The pool range and everything else works as intended.

so I assumed that except for the two DHCP option DHCP works with XOS and the client receive a ip from the XOS DHCP. However, according to your last information, the client does not get an address from the DHCP server on the XOS switch. Is that correct?
I.e. the client has never received IP addresses from DHCP on the XOS switch, right?

Normaly you should see in both cases.

Discover
Offer
Request
ACK

Re: DHCP server not working for iPXE

excessive — Wed, 13 Jan 2021 22:10:01 GMT

Indeed, I wrote this and I can confirm that it works. I’ve set different range of addresses for both scenarios and right now the computer in front of me is working with ip address received from the pool of the switch (192.168.230.200 - 192.168.230.220). I realize how strange it may look, but that’s how it is.

Re: DHCP server not working for iPXE

StephanH — Wed, 13 Jan 2021 22:16:54 GMT

Hmm, if a client get an ip address from an dhcp all for packets I wrote have to be here. Therefore the packets are missing in your trace. Discover and Request go into the same direction. Maybe you are logging only one direction?

Re: DHCP server not working for iPXE

excessive — Wed, 13 Jan 2021 22:31:30 GMT

I don’t have significant experience with Wireshark, but I’m doing exactly the same thing as I did with my working scenario. Just filtering everything with “bootp”. I’m capturing those frames using a Windows machine on the same subnet with interface in promiscuous mode.

Re: DHCP server not working for iPXE

StephanH — Wed, 13 Jan 2021 22:40:29 GMT

In that way you are tracing you will see only broadcasts. The Offer can be a unicast and the ACK will be a unicast and a unicast will not reach you station. Therefore you have to create an mirror port or you can trace directly on the device getting the ip address.

Re: DHCP server not working for iPXE

excessive — Thu, 14 Jan 2021 17:48:51 GMT

Hi Stephan. Thank you for your time.
This morning I mirrored the port to the port of my Wireshark computer. Now I got ONLY Offer and ACK frames. Here they are:

Frame 124877: 337 bytes on wire (2696 bits), 337 bytes captured (2696 bits) on interface \Device\NPF_{4C63F991-A548-48B3-A772-5278B943AE7F}, id 0
Ethernet II, Src: ExtremeN_9b:8e:d0 (00:04:96:9b:8e:d0), Dst: 82:5d:c6:8a:7e:48 (82:5d:c6:8a:7e:48)
Internet Protocol Version 4, Src: 192.168.230.253, Dst: 192.168.230.200
User Datagram Protocol, Src Port: 67, Dst Port: 68
Dynamic Host Configuration Protocol (Offer)
    Message type: Boot Reply (2)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0x1d398b73
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 192.168.230.200
    Next server IP address: 0.0.0.0
    Relay agent IP address: 0.0.0.0
    Client MAC address: 82:5d:c6:8a:7e:48 (82:5d:c6:8a:7e:48)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (51) IP Address Lease Time
    Option: (53) DHCP Message Type (Offer)
    Option: (1) Subnet Mask (255.255.255.0)
    Option: (54) DHCP Server Identifier (192.168.230.253)
    Option: (3) Router
    Option: (6) Domain Name Server
    Option: (66) TFTP Server Name
    Option: (67) Bootfile name
    Option: (255) End

Frame 137003: 337 bytes on wire (2696 bits), 337 bytes captured (2696 bits) on interface \Device\NPF_{4C63F991-A548-48B3-A772-5278B943AE7F}, id 0
Ethernet II, Src: ExtremeN_9b:8e:d0 (00:04:96:9b:8e:d0), Dst: 82:5d:c6:8a:7e:48 (82:5d:c6:8a:7e:48)
Internet Protocol Version 4, Src: 192.168.230.253, Dst: 192.168.230.200
User Datagram Protocol, Src Port: 67, Dst Port: 68
Dynamic Host Configuration Protocol (ACK)
    Message type: Boot Reply (2)
    Hardware type: Ethernet (0x01)
    Hardware address length: 6
    Hops: 0
    Transaction ID: 0x1d398b73
    Seconds elapsed: 0
    Bootp flags: 0x0000 (Unicast)
    Client IP address: 0.0.0.0
    Your (client) IP address: 192.168.230.200
    Next server IP address: 0.0.0.0
    Relay agent IP address: 0.0.0.0
    Client MAC address: 82:5d:c6:8a:7e:48 (82:5d:c6:8a:7e:48)
    Client hardware address padding: 00000000000000000000
    Server host name not given
    Boot file name not given
    Magic cookie: DHCP
    Option: (51) IP Address Lease Time
    Option: (53) DHCP Message Type (ACK)
    Option: (1) Subnet Mask (255.255.255.0)
    Option: (54) DHCP Server Identifier (192.168.230.253)
    Option: (3) Router
    Option: (6) Domain Name Server
    Option: (66) TFTP Server Name
    Option: (67) Bootfile name
    Option: (255) End

Re: DHCP server not working for iPXE

StephanH — Thu, 14 Jan 2021 17:54:09 GMT

Greate, what we see is that option 66 and option 67 are present, that’s good. Normaly you should be able to expant the single option by clicking in wireshark. Can you do this for Option 66 ind 67? Then we will see what is the content of the options.

Re: DHCP server not working for iPXE

excessive — Thu, 14 Jan 2021 18:02:31 GMT

Option: (66) TFTP Server Name
    Length: 4
    TFTP Server Name: ���3


Option: (67) Bootfile name
    Length: 13
    Bootfile name: undionly.kpxe

Seems like option 66 is in wrong format, or for some reason looks unreadable.

67 seems to be correct.

Re: DHCP server not working for iPXE

StephanH — Thu, 14 Jan 2021 18:11:32 GMT

Hello, yes that’s the point. How does the according config line looks like in your switch?

Re: DHCP server not working for iPXE

StephanH — Thu, 14 Jan 2021 18:12:48 GMT

You can try to use “string” as type and set the ip like “192.168.x.x”

Re: DHCP server not working for iPXE

excessive — Thu, 14 Jan 2021 18:14:32 GMT

DHCP Address Range   : 192.168.230.200->192.168.230.220
    Netlogin Lease Timer : Not configured (Default = 10 seconds)
    DHCP Lease Timer     : 86400 seconds
    Default Gateway      : 192.168.230.253
    Primary DNS Server   : xx.xx.xx.xx
    DHCP Option Code  66 : ipaddress 192.168.230.51
    DHCP Option Code  67 : string "undionly.kpxe"
    Ports DHCP Enabled   : 1:21,3:16

Here it is. I’ve selected “ipaddress” for option code 66 as it seems logical to me.

Re: DHCP server not working for iPXE

StephanH — Thu, 14 Jan 2021 18:18:02 GMT

Because of option 66 is defined as the TFTP server name, I assume your server is looking for a string maybe.

Re: DHCP server not working for iPXE

excessive — Thu, 14 Jan 2021 18:21:05 GMT

Changed it to string. The option now is readable in the frame:

Option: (66) TFTP Server Name
    Length: 14
    TFTP Server Name: 192.168.230.51

but unfortunately the end result is the same. My client machine still doesn’t download the kpxe file and produces same error as in my initial post.

I can see that on my working example I do have value for “Next server IP address:”
Here it is missing.