Is there a reason to keep dhcpcd running after an Internet connection is established? - Re: Systemd service life cycle

[Robert Heller]

At Wed, 13 Apr 2016 14:37:14 -0400 "Ubuntu user technical support,  not for general discussions" <ubuntu-users at lists.ubuntu.com> wrote:

> 
> On 16-04-13 02:13 PM, Ralf Mardorf wrote:
> > So what is continuing running the daemon good for after the Internet 
> > connection is established?
> 
> IP Addresses are leased from the DHCP server for a fixed amount of 
> time.  The DHCPCD daemon is responsible for renewing that lease before 
> it expires, (and, if requested by the server at that time, change the IP 
> address of the client.)
> 
> I have no idea how the ISP's system will react if a system keeps using 
> an IP address after a lease for it has expired and not been renewed, but 
> I suspect the short answer is "Don't do that."

Typical behaviour on a LAN DHCP server is to recycle the IP address if it is 
not renewed.  If a node uses an 'expired' IP address that has been recycled to 
another node, then you have two nodes with the same IP address.  Then you have 
a relly big OPPS! situation:  Will the *real* 192.168.0.27, please stand up? 
No, there can't be two of you, there can be only one... 

While, many ISP (and some LANs) might provide IP Addresses with *very long 
lease times*, the lease time is never "forever".  On the LANs I manage where 
the DHCP server gives out 'static' (fixed) IP addresses to selected MAC 
addresses, it is still for a fixed time and yes, the IP address won't actually 
get recycled, but the nodes in question don't (can't) know that, so yes, the 
dhcp client daemon will be running (idling quietly in the background).  It is 
possible that ISPs might actually assign a 'fixed' IP address to a given 
customer with a given MAC address, there is no certainly of that.  *Most* of 
the time the IP address lease can be renewed an indefiniate number of times 
(if it is a 'random' address), but again there is no certainity.

> 
> 
> 

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