DHCP client always using broadcast as the destination

Reception, channel detection, network issues, CableCARD setup, etc.
Post Reply
sdust
Posts: 45
Joined: Sat Jun 05, 2021 3:39 am
x 1

DHCP client always using broadcast as the destination

Post by sdust »

Looking at network activity of CONNECT 4K it seems the DHCP client does not remember the DHCP server address and always sends DHCP messages to the broadcast address.

Code: Select all

10:18:56.625714 00:18:dd:XX:XX:XX > ff:ff:ff:ff:ff:ff, ethertype IPv4 (0x0800), length 342: (tos 0x0, ttl 64, id 27893, offset 0, flags [DF], proto UDP (17), length 328)
    192.168.0.234.68 > 255.255.255.255.67: BOOTP/DHCP, Request from 00:18:dd:XX:XX:XX, length 300, xid 0x7a2e7c08, Flags [Broadcast]




HDHomeRun CONNECT 4K
Model: HDHR5-4K
Firmware: 20210224

jasonl
Expert
Posts: 15578
Joined: Sun Oct 28, 2007 9:23 pm
x 33

Re: DHCP client always using broadcast as the destination

Post by jasonl »

Per RFC 2131, the client has the option of using either broadcast or unicast for the DHCPREQUEST.

sdust
Posts: 45
Joined: Sat Jun 05, 2021 3:39 am
x 1

Re: DHCP client always using broadcast as the destination

Post by sdust »

jasonl wrote: Mon Jun 07, 2021 8:34 pm Per RFC 2131, the client has the option of using either broadcast or unicast for the DHCPREQUEST.
And HomeRun is the only device flooding the network with the unnecessary broadcast. :D

nickk
Silicondust
Posts: 16890
Joined: Tue Jan 13, 2004 9:39 am
x 86

Re: DHCP client always using broadcast as the destination

Post by nickk »

sdust wrote: Mon Jun 07, 2021 10:51 pm
jasonl wrote: Mon Jun 07, 2021 8:34 pm Per RFC 2131, the client has the option of using either broadcast or unicast for the DHCPREQUEST.
And HomeRun is the only device flooding the network with the unnecessary broadcast. :D
2 packets every 12 hours (assuming a 24 hour lease).

sdust
Posts: 45
Joined: Sat Jun 05, 2021 3:39 am
x 1

Re: DHCP client always using broadcast as the destination

Post by sdust »

nickk wrote: Mon Jun 07, 2021 11:42 pm
sdust wrote: Mon Jun 07, 2021 10:51 pm
jasonl wrote: Mon Jun 07, 2021 8:34 pm Per RFC 2131, the client has the option of using either broadcast or unicast for the DHCPREQUEST.
And HomeRun is the only device flooding the network with the unnecessary broadcast. :D
2 packets every 12 hours (assuming a 24 hour lease).
The lease time on my network is 10 minutes in line with AWS. I also think if something is worth doing it is worth doing right. I will refrain from enumerating the many areas where the quality of Silicon Dust engineering does not shine and results in unnecessary suffering of its users. ;)

Edit: A well behaved DHCP client when the IP address of the DHCP server is already known uses unicast. It doesn't also set the broadcast flag on the request which makes the server sending the reply use broadcast as well. This makes watching traffic from/to the device unnecessary difficult.

NedS
Silicondust
Posts: 2088
Joined: Mon Dec 10, 2018 12:38 pm
x 55

Re: DHCP client always using broadcast as the destination

Post by NedS »

I also think if something is worth doing it is worth doing right.
That statement is in direct contrition to this statement:
The lease time on my network is 10 minutes
A ten minute lease time is absurd for a home network. You are creating your own problem and asking us to fix it.

sdust
Posts: 45
Joined: Sat Jun 05, 2021 3:39 am
x 1

Re: DHCP client always using broadcast as the destination

Post by sdust »

NedS wrote: Tue Jun 08, 2021 1:50 am
I also think if something is worth doing it is worth doing right.
That statement is in direct contrition to this statement:
The lease time on my network is 10 minutes
A ten minute lease time is absurd for a home network. You are creating your own problem and asking us to fix it.
Let's say I have quite a few devices on my network but I would not call the setup absurd. That's uncalled for. ;)

nickk
Silicondust
Posts: 16890
Joined: Tue Jan 13, 2004 9:39 am
x 86

Re: DHCP client always using broadcast as the destination

Post by nickk »

A 10 minute lease time is fine. I did the initial development-test with a 60s lease time.

I wrote that code about 10 years ago so a quick revisit is reasonable - I will take a look.

Nick

Post Reply