[syslinux] Cannot chain to another PXE server on the same subnet

[Gene Cumm]

On Fri, Mar 7, 2014 at 2:33 AM, Vieri <rentorbuy at yahoo.com> wrote:

> So I take it it's more of a DHCP hack in which:
> 1- client boots and gets DHCP response from 10.215.144.7 with PXE syslinux info
> 2- client loads pxelinux.0 menu and selects menu that chains to Altiris PXE menu except, instead of calling pxechain.com or pxechn.c32 with the Altiris server's IP address, the client should "re-netboot" but this time, the DHCP server at 10.215.144.7 should not include any PXE information at all for this particular client/MAC, so Altiris can kick in.
>
> I don't know how to do this but is this basically what you're suggesting?

1) Thinking about the responses again, I'm absolutely surprised that
you can even boot PXELINUX.  I would have expected the response from
the Altiris server to override your attempts to block it.

2) There's at least one more thing we can try, a very long option 43.
Either use the text-decimal tcpdump or a tool that can read the pcap
(like Wireshark) and create a single large colon-separated string
representation of the 3 option 43 values (should be over 1200
characters long, 3 times total length minus 1).

Using wireshark and right-clicking on each option 43 instance, copy,
bytes, as hexstream, and leaving the option 255s in I get:

01:04:e0:01:01:03:02:02:de:06:03:02:df:06:04:01:01:05:01:01:06:01:0b:08:70:aa:aa:01:0a:d7:90:3c:00:a0:01:0a:d7:90:3c:00:81:01:0a:d7:90:3c:00:a1:01:0a:d7:90:3c:00:a2:01:0a:d7:90:3c:00:a4:01:0a:d7:90:3c:00:a5:01:0a:d7:90:3c:00:a6:01:0a:d7:90:3c:00:a7:01:0a:d7:90:3c:00:a8:01:0a:d7:90:3c:00:a9:01:0a:d7:90:3c:00:aa:01:0a:d7:90:3c:00:ab:01:0a:d7:90:3c:00:ac:01:0a:d7:90:3c:00:83:01:0a:d7:90:3c:bb:bb:01:0a:d7:90:3c:ff:09:cb:00:00:16:4e:65:78:74:20:44:65:76:69:63:65:20:28:42:49:4f:53:2f:45:46:49:29:00:a0:0c:55:62:75:6e:74:75:4e:65:74:78:38:36:00:81:08:44:4f:53:20:55:4e:44:49:00:a1:0c:48:50:20:64:63:37:38:30:30:53:46:46:00:a2:0b:44:65:6c:6c:20:4f:70:74:33:36:30:00:a4:0b:47:58:35:32:30:26:47:58:36:32:30:00:a5:16:42:72:6f:61:64:4e:65:74:58:74:72:65:6d:65:20:49:49:20:47:69:67:61:00:a6:11:44:65:6c:6c:4f:70:74:47:58:36:30:20:45:31:30:30:62:00:a7:0e:44:72:61:67:65:72:20:52:54:4c:38:31:33:39:00:a8:05:6c:69:6e:75:78:00:aa:06:76:6d:77:61:72:65:00:ab:0a:48:50:38:30:30:30:45:53:46:46:00:ac:06:44:65:6c:6c:50:45:00:83:05:57:69:6e:50:45:0a:2e:05:50:72:65:73:73:20:5b:46:38:5d:20:74:6f:20:53:65:6c:65:63:74:20:61:20:62:6f:6f:74:20:6f:70:74:69:6f:6e:3a:20:49:4e:46:2d:56:4d:2d:44:53:ff:47:04:00:00:00:00:e0:02:00:00:ff

So try "-o 43.x=<above-string>" on the append line.  If that doesn't
work, strip the two "ff"s in the middle.  Otherwise, this is going to
need rework for the pack/unpack and pxechn.c32

-- 
-Gene