DHCPOFFER log with empty MAC

YC ycflash at gmail.com
Sat Dec 24 17:21:30 UTC 2016 

Hi, I'm seeing some DHCPOFFER logs with empty logs:

DHCPOFFER on 10.28.129.242 to "" (iPhone-6) via 10.28.128.1

It have rarely been seen, only 3 or few logs happens in a day.

At first, I tried to tcpdump with 'udp[10] != 0x06' to capture packet 
that may contains no MAC in it, but no luck.

Then, I added debug statement to dhcp_reply() function where DHCPOFFER 
message logged from, as bellow:

         if (lease -> hardware_addr.hlen <= 1 && 0 == strcmp("\"\"", 
print_hex_1(lease->uid_len, lease->uid, 60))) {
                 dump_packet(state->packet);
                 dump_raw ((unsigned char *)state->packet->raw, 
state->packet->packet_length);
                 dump_raw ((unsigned char *)&raw, packet_length);
         }

When the situation happens again, the log output of debug statements(as 
bellow) seems the packet dhcpd was dealing it a wrong DHCP packet and 
followed by a bogus hlen message.

dhcpd[18972]: DHCPOFFER on 10.28.129.242 to "" (iPhone-6) via 10.28.128.1
dhcpd[18972]: packet length 300
dhcpd[18972]: op = 255  htype = 255  hlen = 255  hops = 255
dhcpd[18972]: xid = 0  secs = 10968  flags = f2ef
dhcpd[18972]: ciaddr = 252.127.0.0
dhcpd[18972]: yiaddr = 80.45.239.242
dhcpd[18972]: siaddr = 0.0.0.0
dhcpd[18972]: giaddr = 32.255.255.255
dhcpd[18972]: chaddr = fc:7f:00:00:0e:00
dhcpd[18972]: filename = 1
dhcpd[18972]: server_name = 1
dhcpd[18972]:   option dhcp-lease-time 7776000;
dhcpd[18972]:   option dhcp-message-type 1;
dhcpd[18972]:   option dhcp-parameter-request-list 1,3,6,15,119,252;
dhcpd[18972]:   option dhcp-max-message-size 1500;
dhcpd[18972]:   option host-name "iPhone-6";
dhcpd[18972]:   option dhcp-client-identifier 1:24:24:e:dc:fd:d7;
dhcpd[18972]:
dhcpd[18972]: 000: 02 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 010: 80 2d ef f2 fc 7f 00 00  60 0f d5 e3 31 00 00 00 
.-......`...1...
dhcpd[18972]: 020: cd 5c 49 00 00 00 00 00  78 82 c6 e3 31 00 00 00 
.\I.....x...1...
dhcpd[18972]: 030: c6 70 d5 e3 31 00 00 00  00 00 00 00 00 00 00 00 
.p..1...........
dhcpd[18972]: 040: 80 2d ef f2 fc 7f 00 00  70 2d ef f2 fc 7f 00 00 
.-......p-......
dhcpd[18972]: 050: 03 00 00 00 00 00 00 00  a0 2e ef f2 fc 7f 00 00 
................
dhcpd[18972]: 060: ce 5c 49 00 00 00 00 00  67 41 c4 e3 31 00 00 00 
.\I.....gA..1...
dhcpd[18972]: 070: cf 5c 49 00 00 00 00 00  00 00 00 00 00 00 00 00 
.\I.............
dhcpd[18972]: 080: 01 00 00 00 00 00 00 00  58 2b ef f2 fc 7f 00 00 
........X+......
dhcpd[18972]: 090: 00 00 00 00 00 00 00 00  20 2c ef f2 00 00 00 00 
........ ,......
dhcpd[18972]: 0a0: a0 e5 f8 e3 31 00 00 00  00 00 00 00 00 00 00 00 
....1...........
dhcpd[18972]: 0b0: 60 2c ef f2 fc 7f 00 00  af 09 00 00 00 00 00 00 
`,..............
dhcpd[18972]: 0c0: ca 5c 49 00 00 00 00 00  8c 6b d5 e3 31 00 00 00 
.\I......k..1...
dhcpd[18972]: 0d0: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 0e0: cc 2c ef f2 fc 7f 00 00  e8 2c ef f2 fc 7f 00 00 
.,.......,......
dhcpd[18972]: 0f0: 00 00 00 00 00 00 00 00  08 2d ef f2 fc 7f 00 00 
.........-......
dhcpd[18972]: 100: 00 ff ff ff 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 110: ae 87 21 41 36 00 00 00  20 00 00 00 00 00 00 00 
..!A6... .......
dhcpd[18972]: 120: 00 00 00 00 00 00 00 00  f8 2b ef f2 
.........+..
dhcpd[18972]: 000: 02 01 ff 01 05 a9 b0 fc  00 09 00 00 00 00 00 00 
................
dhcpd[18972]: 010: 0a 1c 81 f2 00 00 00 00  0a 1c 80 01 24 24 0e dc 
............$$..
dhcpd[18972]: 020: fd d7 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 030: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 040: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 050: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 060: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 070: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 080: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 090: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 0a0: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 0b0: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 0c0: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 0d0: 00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00 
................
dhcpd[18972]: 0e0: 00 00 00 00 00 00 00 00  00 00 00 00 63 82 53 63 
............c.Sc
dhcpd[18972]: 0f0: 35 01 02 36 04 0a 03 09  02 33 04 00 00 2b eb 01 
5..6.....3...+..
dhcpd[18972]: 100: 04 ff ff fc 00 03 04 0a  1c 80 01 06 0c 0a 03 09 
................
dhcpd[18972]: 110: 06 0a 03 09 05 0a 03 09  04 0f 0b 62 75 70 74 2e 
...........bupt.
dhcpd[18972]: 120: 65 64 75 2e 63 6e ff 00  00 00 00 00 
edu.cn......
dhcpd[18972]: Discarding packet with bogus hlen.

Any sugguestion how to resovle this? Thanks!

-- 
yc.

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