Mailinglist Archive: opensuse (1047 mails)

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Re: [opensuse] Network set up after crash
On 01/15/2016 01:15 PM, don fisher wrote:
But I have never been able to get the dynamically assigned IP address
associated with host name.

What are you using as a DHCP server and how is it configured?

A DHCP server can either respond to a host that 'knows' its name and
tells the DHCP server. Or the DHCP server can assign a name.

Its all in the configuration!

In the past, I've set up a firewall, on other occasions a main server,
as the DHCP server and gone to a lot of length to make sure the DHCP
config has the 'smarts' to make the network look and behave like I want.
The thing is that there are a LOT of ways to do this and a lot of
options. It all depends on the hardware and software. Its difficult
to make sweeping generalities.

On another occasion, I started with DHCP and noted everything ..
*EVERYTHING* .. about the network config on the one host and re-entered
that for static values.

Oh, and it broke the network.
That was because I'd hard coded an address that is in the DHCP 'pool'.
"Well, don't do that!".

If you want names to match up then you need to have DNS and DHCP tightly
integrated. The 'dnsmasq' program is one way to do that, if you are
using that on the 'server'. As Per says, its doable but irrelevant in
the case you've been describing.

There is a big caveat on all this:
This works for me because my network is behind my firewall. My firewall
on the 'red' side does DHCP negotiation with the vendor supplied cable
modem. On the 'blue' side it hands out dynamic addresses in the range
.100 to .200 to wifi devices. All my statically wired devices have
static addresses under .64.

If, however, your computer connects to the vendor cable modem (or fibre
or DSL-whatever) directly and you start with DHCP, note the values, then
hard code them statically, you've set yourself up for a fall.
The reaon the vendor is using DHCP in the first place is resource
management; some time in the future your 'public' address may change and
that static value is now invalid.


One of the reasons many vendors use DHCP and ship devices that get used
as routers with DHCP as the default is that if you simply use it then
its idiot simple and ought to be idiot-proof. However its also one of
those cases where "a little knowledge is a dangerous thing".

A single hosted machine such as you have described needs only three
routes, and they should be set up without the need for manual tweeking.

1. The loopback
127.0.0.0/8 dev lo

2. The LAN
host-ip/24 dev Ethernet

3. The default if nothing else is matched
This should go to the router

Its up to the router to decide whether to send the packet to the
Internet or to another LAN segment. How the router is configured,
whether its set up statically, uses DHCP, uses a 'discovery protocol',
is beyond the scope of what we're discussing here.
BTDT.

In the worst case, if your DHCP is a mess, you may have to enter #3
manually, but there is no reason you should have to enter #1 or #2
manually.


--
A: Yes.
> Q: Are you sure?
>> A: Because it reverses the logical flow of conversation.
>>> Q: Why is top posting frowned upon?

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