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Buffalo WLAE-AG300N DHCP client is buggy and adds a NULL character to the host name.

Posted by jpluimers on 2016/05/13

Buffalo WLAE-AG300N is one of those buggy DHCP clients… Even running firmware Ver.1.85 (R1.05/B1.00)), it gets the length of the DHCP host name wrong so adds a bogus NULL byte to that name.

@Buffalo: please fix this.

The DHCP client options are of structure Type/Length/Value so a client is supposed to set the length of the hostname to exactly the number of characters.
However there exist buggy clients that either send a length of 1 more and a \00 at the end of the name, or send a fixed length and pad it with \00 as necessary.

Source: DHCP server: Odd active hostname behaviour: some views have null character at the end, some don’t. – MikroTik RouterOS

Fromt a packet capture:

Buffalo WLAE-AG300N gets the length of the DHCP name wrong and inserts an extra NULL character.

Buffalo WLAE-AG300N gets the length of the DHCP name wrong and inserts an extra NULL character.

This besides these devices also not automatically powering up when power goes out and comes back up

Mikrotik packet capture and viewing it in Wireshark

Anyway: getting and displaying the packet capture was quite easy:

  1. In Winbox (or from the console):
    1. Tools ->
    2. Packet Sniffer ->
    3.  General tab: set filename and file limit, then click Apply
    4. Filter tab: choose the interface, protocol (UDP) and port (67), then click Apply
    5. Click Start
    6. Wait for the DHCP refresh to happen
    7. Click Stop
  2. In Winbox (or from the console):
    1. Files -> Choose the captured file -> Download
  3. In your file manager, ensure the downloaded file gets the .pcap extension
  4. In Wireshark: load the .pcap file and inspect it

 

–jeroen

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