[Bug 2215] BusyBox 1.17.0 fails to retrieve IP from DHCP

[bugzilla at busybox.net]

https://bugs.busybox.net/show_bug.cgi?id=2215

--- Comment #4 from Denys Vlasenko <vda.linux at googlemail.com>  ---
Here is 1.16.1 request packet:

19:51:48.642325 IP (tos 0x0, ttl  64, id 0, offset 0, flags [none], proto: UDP
(17), length: 576)
 0.0.0.0.bootpc > 255.255.255.255.bootps: [udp sum ok]
 BOOTP/DHCP, Request from 00:0c:29:25:6b:ae (oui Unknown), length: 548,
xid:0xa11106b, flags: [Broadcast] (0x8000)
          Client Ethernet Address: 00:0c:29:25:6b:ae (oui Unknown)
          Vendor-rfc1048:
            DHCP:DISCOVER
            CID:[ether]00:0c:29:25:6b:ae
            HN:"box"
            VC:"udhcp 1.16.1"
            MSZ:576
            PR:SM+DG+NS+HN+DN+BR+NTP
        0x0000:  4500 0240 0000 0000 4011 78ae 0000 0000  E.. at ....@.x.....
        0x0010:  ffff ffff 0044 0043 022c 576d 0101 0600  .....D.C.,Wm....
        0x0020:  0a11 106b 0000 8000 0000 0000 0000 0000  ...k............
        0x0030:  0000 0000 0000 0000 000c 2925 6bae 0000  ..........)%k...
        0x0040:  0000 0000 0000 0000 0000 0000 0000 0000  ................
...
        0x00f0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
        0x0100:  0000 0000 0000 0000 6382 5363 3501 013d  ........c.Sc5..=
        0x0110:  0701 000c 2925 6bae 0c03 626f 783c 0c75  ....)%k...box<.u
        0x0120:  6468 6370 2031 2e31 362e 3139 0202 4037  dhcp.1.16.19.. at 7
        0x0130:  0701 0306 0c0f 1c2a ff00 0000 0000 0000  .......*........
        0x0140:  0000 0000 0000 0000 0000 0000 0000 0000  ................
...
        0x0230:  0000 0000 0000 0000 0000 0000 0000 0000  ................

and 1.17.0 request packet:

19:52:46.847263 IP (tos 0x0, ttl  64, id 0, offset 0, flags [none], proto: UDP
(17), length: 313)
 0.0.0.0.bootpc > 255.255.255.255.bootps: [udp sum ok]
 BOOTP/DHCP, Request from 00:0c:29:25:6b:ae (oui Unknown), length: 285,
xid:0x4cbb4e39, flags: [none] (0x0000)
          Client Ethernet Address: 00:0c:29:25:6b:ae (oui Unknown)
          Vendor-rfc1048:
            DHCP:DISCOVER
            CID:[ether]00:0c:29:25:6b:ae
            HN:"box"
            VC:"udhcp 1.17.0"
            MSZ:576
            PR:SM+DG+NS+HN+DN+BR+NTP
        0x0000:  4500 0139 0000 0000 4011 79b5 0000 0000  E..9.... at .y.....
        0x0010:  ffff ffff 0044 0043 0125 5903 0101 0600  .....D.C.%Y.....
        0x0020:  4cbb 4e39 0000 0000 0000 0000 0000 0000  L.N9............
        0x0030:  0000 0000 0000 0000 000c 2925 6bae 0000  ..........)%k...
        0x0040:  0000 0000 0000 0000 0000 0000 0000 0000  ................
...
        0x00f0:  0000 0000 0000 0000 0000 0000 0000 0000  ................
        0x0100:  0000 0000 0000 0000 6382 5363 3501 013d  ........c.Sc5..=
        0x0110:  0701 000c 2925 6bae 0c03 626f 783c 0c75  ....)%k...box<.u
        0x0120:  6468 6370 2031 2e31 372e 3039 0202 4037  dhcp.1.17.09.. at 7
        0x0130:  0701 0306 0c0f 1c2a ff                   .......*.

As you see, it is shorter. But this should be ok - Windows also uses unpadded
packets. Ideas so far:
* old packet has bcast flag in dhcp header. (1) Why? and (2) why new one
doesn't?
* maybe your server insists on packets rounded up to 2 or 4 byte boundary in
size?

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