Re: [gentoo-user] Linksys router BEFSR41 loosing internet

[William Kenworthy]

On Sun, 2010-12-19 at 05:53 -0600, Dale wrote:
> Peter Humphrey wrote:
> > On Sunday 19 December 2010 10:10:56 Dale wrote:
> >
> >
> >> It's pretty simple tho.  Computer>>  router>>  DSL modem>>  internet.
> >>
> > Seems to me that the only place you need DHCP is on the DSL side of the
> > modem, so that it can request an address from your ISP. If you pay them
> > for a static address, that's the one you'll get; otherwise of course
> > it'll vary from one occasion to another.
> >
> > On the inner side of the DSL modem I suggest you fix an address, say
> > 192.168.0.1, then 192.168.0.2 on the router's modem interface, then
> > 192.168.1.1 on the router's LAN interface. All those with a 24-bit mask
> > for simplicity. (I used to use a 29-bit mask, but that only leaves six
> > addresses free and it was too restrictive.)
> >
> > You could run DHCP in the router if you wanted to, to save yourself
> > setting manual addresses on your computers, but personally I don't
> > bother with DHCP as I prefer to know what address belongs to which
> > interface. It's not as though I had hundreds of boxes to keep abreast
> > of, after all.
> >
> >
>
> This was fun.  I tried to set it up the way you explained but apparently
> I ain't to good with this.  Now the router don't work at all and I had
> to hit the reset button on the modem.  I'm glad I could remember the
> password.  :/
>
> OK.  The IP I get from AT&T is set by them and it changes.  I think that
> is dynamic not static.  So, I assume that part of the connection has to
> be DHCP.  Correct?  That was how I left it anyway.
>
> Where does this network idiot go from here?  I think the modem got mad
> when I told it to let the router set the IP between it and the modem.
> The computer seemed to talk to the router just fine but had not internet
> IP address.  It was blank.
>
> Dale
>
> :-)  :-)
>
> P. S.  Going to look for a howto to see if it at least helps me
> understand how this works.
>

Dale, 

point 1 is that the problem you seem to have is that your two dhcp
systems are each giving out IP's from the same range, and as both are
starting at the same number, thats where the clash occurs.  Simple fix
is to change the ranges so they dont overlap.  Bottom line, you should
have only one dhcp server per network (as defined by the subnet mask)
unless you pin IP numbers (as in bootp),  use different ranges for each
or other trickery.  Or statically assign ip numbers and be done with it!

Point 2 is dhcp is non-routable as it broadcasts (as always, there are
ways to deal with this - but I dont think you have dhcp-relay going on.)
- dhcp clients broadcast for an address, and the server sends the
address back unicast - so clients on different network segments cant see
others broadcasts - for instance a layer 3 router blocks broadcasts.

point 3 is that the adsl modem is normally a dhcp client to the external
network (as its ip address is supplied by the ISP), and a server for the
internal network to supply IP numbers from its own pool of addresses to
your internal machines.

Point 4 is that the network design sucks.  Can you list what ip
number/subnet mask you have on the internal PC, the router internal
interface, the router external interface and the adsl modem internal
interface.  And on which device the NAT/firewall is happening (please
done say both ... :(

Point 5 ... thats enuf for now :)


BillK




-- 
William Kenworthy <billk@×××××××××.au>
Home in Perth!