Trying to capture DHCP packets (discover, offer, request, ack)

dhcp

asked 2020-02-18 19:56:20 +0000

dcalcutt
1 ●1 ●1

updated 2020-02-19 11:21:35 +0000

grahamb

flag of United Kingdom of Great Britain and Northern Ireland

23790 ●4 ●950 ●227 https://www.wireshark.org

I'm having issues with IoT devices, specifically Lifx bubs.

when I first turn on the bulbs, they connect well...

then after a period of time the device are not connected to the network.

I do see in the system log file, the device is discovered, offer, and then nothing else, but the discover and offer are repeated again and again. SO the device never get connected.

So I'm trying to capture the packets with Wireshark now.

I set the screen display filter to DHCP.

I only get the Discover, and Offer request, but no ACK.

Any suggestions? I know they are there... when you first turn on the bulb.

edit retag flag offensive close merge delete

Comments

Where is the capture being done (on the DHCP server?) and what type of network is it (WiFi, switched, ?)?

Chuckc ( 2020-02-18 20:07:07 +0000 )edit

All my bulbs are on 2.4 connected to one of four access points. Each access point is teathered to the main router. The desktop I’m using Wireshark on is on a switch connected to the main router.

Should I move the desktop connection to the main router?

dcalcutt ( 2020-02-18 23:50:48 +0000 )edit

add a comment

answered 2020-02-19 04:47:36 +0000

Chuckc
2818 ●5 ●567 ●19

The destination ethernet address for DHCP can be the broadcast address (ff:ff:ff:ff:ff:ff)or a specific device MAC address. See the DHCP RFC (https://www.ietf.org/rfc/rfc2131.txt) for info about when unicast and broadcast addresses are valid.

A switch only sends packets out a port that are either addressed to the attached device or to the broadcast address. Any DHCP packets being sent to the bulb MAC addresses won't be sent to the desktop switch port.

Moving the desktop to the router will help but you will also need to configure that port to be a Monitor port to see all traffic. Capture configuration and when to use a Monitor port are covered here: https://wiki.wireshark.org/CaptureSet...

edit flag offensive delete link

add a comment

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Trying to capture DHCP packets (discover, offer, request, ack)

Comments

1 Answer

Your Answer

Question Tools

Stats

Related questions

Trying to capture DHCP packets (discover, offer, request, ack) edit

Comments

1 Answer

Your Answer

Question Tools

Stats

Related questions

Trying to capture DHCP packets (discover, offer, request, ack)