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After some time I have finally been able to reconfigure the network on my NVidia Jetson after the ethernet stopped working abruptly. I hope that by understanding what exactly is happening in the lines below I can better understand what is occurring when my computer communicates with my router.

  • What does the listening on and sending on information mean and stand for?
  • What is an xid?
  • Why port 67?
  • Who is sending DHCPDISCOVER, and who is sitting at 255.255.255.255?
  • What are the various odd numbered intervals 3, 5, 12, 67?
  • Why finally is a DHCPREQUEST made, and who decided the ip address requested?
ubuntu@tegra-ubuntu:~$ sudo ifdown eth0
RTNETLINK answers: No such process
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/00:04:4b:26:fd:7b
Sending on   LPF/eth0/00:04:4b:26:fd:7b
Sending on   Socket/fallback
DHCPRELEASE on eth0 to 10.0.0.1 port 67 (xid=0x7b85fd90)
ubuntu@tegra-ubuntu:~$ sudo ifup eth0
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/00:04:4b:26:fd:7b
Sending on   LPF/eth0/00:04:4b:26:fd:7b
Sending on   Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 3 (xid=0x37e8201)
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 5 (xid=0x37e8201)
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 12 (xid=0x37e8201)
DHCPREQUEST of 10.0.0.35 on eth0 to 255.255.255.255 port 67 (xid=0x37e8201)
DHCPOFFER of 10.0.0.35 from 10.0.0.1
DHCPACK of 10.0.0.35 from 10.0.0.1
bound to 10.0.0.35 -- renewal in 275106 seconds.
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    The interval 3, 5, 12 are timeouts, which are randomized and are longer and longer as they DHCPDISCOVER not getting any answer from a server and times out. The third DHCPDISCOVER sent reached the DHCP-server and it got an answer before the "12" timeout.
    – Anders
    Nov 12, 2014 at 0:59

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This looks like a typical set of DHCP client operations when a DHCP address is released (on ifdown) and then acquired (on ifup).

The listening and sending parts are related to which interfaces is the DHCP client going to operate on (send requests and listen for responses).

xid is defined in RFC2131 - it is a transaction number that allows the DHCP client and server to be on the same page during the message exchange.

Your client is broadcasting DHCPDISCOVER where 255.255.255.255 is the broadcast IP address of the local network. This allows it to find the DHCP server (if such exists on the local network).

Port 67 UDP is a standard DHCP port.

The DHCPREQUEST is sent by your client to the server in an attempt to renew its last known IP address. DHCPOFFER is sent back by the server with the requested IP address by your client. The client acknowledges it back to the server with DHCPACK and finally assigns the UP address to eth0.

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