Re: [gentoo-user] dhcpd versus fixed IP addresses

[Michael]

On Sunday, 4 October 2020 18:31:44 BST Neil Bothwick wrote:
> On Sun, 4 Oct 2020 18:30:08 +0100, Neil Bothwick wrote:
> > On Sun, 4 Oct 2020 13:03:39 -0400, Walter Dnes wrote:
> > >   I decided to get a low-end cable-internet account as backup. 10/1 is
> > >
> > > easily sufficient for 1080p Youtube or 720p Netflix (the max for
> > > Google Chrome on a PC).  I haven't yet received the TC4400 cable
> > > modem, but I understand that it only does dhcp.  Let's see if I have
> > > this right for switching switching my desktop back and forth to/from
> > > dhcpd/fixed IP...
> > >
> > > emerge dhcpcd (one time only)
> > >
> > > From fixed to dhcpc
> > > ===================
> > > Step 1) Rename /etc/conf.d/net and execute "touch /etc/conf.d/net"
> > > Step 2) Manually start up dhcpcd service
> > > Step 3) /etc/init.d/net.eth0 restart
> > >
> > > From dhcpc to fixed
> > > ===================
> > > Step 1) Restore original /etc/conf.d/net
> > > Step 2) Manually kill dhcpcd service
> > > Step 3) /etc/init.d/net.eth0 restart
> > >
> > >   This could cause problems when I want to transfer files between my
> > >
> > > computers.  Here's part of an example /etc/hosts file...
> > >
> > > 192.168.1.249        i3
> > > 192.168.1.250      i660
> > > 192.168.1.251      d531
> > > 192.168.1.2       thimk
> > >
> > >   If IP addresses are assigned at random, this obviously won't work.
> > >
> > > Any suggestions?
> >
> > If you have access to the DHCP server on the existing setup, you could
> > ditch static addresses altogether and set up your server to assign the
> > addresses you want to use. This avoids any shenanigans when switching
> > from one connection to another.
> >
> > Or you could run your own local DHCP server, such as dsnmasq, which
> > gives you full control however you are connected.I used to run dnsmasq
> > on my server but this year switched to running Pi-Hole on a Raspberry
> > Pi. It provides DNS, DHCP (through dnsmasq) and ad blocking all in one
> > place.
>
> However, I would wait until the new modem arrives as most do allow you to
> turn off DHCP for the LAN and the information you have may only apply to
> the WAN connection.

If I understand correctly what the OP is trying to achieve emerging dhcpcd or 
renaming /etc/conf.d/net may be unnecessary/avoidable.  I suspect the word 
"modem" is used here to mean the all-in-one modem + router + LAN switch 'white 
goods', plus potentially a WiFi AP.  I am not familiar with TC4400, but in 
generic terms routers expose some GUI control pages, for users to configure 
the DHCP tables in order to specify static IP addresses corresponding to the 
MACs of the devices on the LAN.  Even if this modem/router doesn't, you can 
set static IP addresses on the LAN PCs themselves without dhcpcd.  As long as 
the PCs do not ask for an address from the router's DHCP server, the static IP 
address they have been configured with should just work.  The caveat here is 
that the subnet for the PCs should be the same as the router's; i.e. 
192.168.1.0/24.

Random (guest) devices connected to the router will still be allocated 
dynamically some IP address by its dhcp server, typically starting from 2 and 
incremented from there.  Since most of your devices IP addresses start from 
the top it's unlikely there'll be clash, because any dynamically allocated IP 
address leases will soon expire.

You could of course set your modem+routers to operate in a 'fully-bridged' 
mode and use a stand alone router to deal with IP address allocation, DNS 
resolving and firewalling for your LAN, plus PPPoE.

You haven't explained if you intend to run a fallback mechanism so the 
standalone router, or clients, switch from one router-ISP to the other in case 
of failure, but for a manual set up the above will suffice.