Re: Public & private IP addresses via IP Aliasing?

Re: Public & private IP addresses via IP Aliasing?

[beolach]

Thanks, Ray.  Dhcp-relay is exactly what I wanted to know about.
Unfortunatly, some of the machines on the local network are
running M$ Windows, which from googling I learn lacks real IP
Aliasing support - you can get multiple static IPs, but not
static & DHCP at the same time.  So at least for the windows
boxes, I will probably switch to DHCP only.  Which brings up a
new question: is there an easy way to change the IP address a
hostname refers to when the machine's IP address changes.  For
example, the host named gamebox crashes, and after reboot has a
different IP than before.  Is there a nice way to tell all the
other computers on the local net that gamebox's address has
changed?  I'm guessing that with how common DHCP is, there must
be a way, but I don't know what it would be.

Thanks again,
Conway S. Smith

-- Ray Olszewski <ray@comarre.com> wrote:
> At 01:22 AM 9/19/2003 +0000, beolach@juno.com wrote:
> 
> > On my home network, I am currently using IP-masquerading (aka NAT)
> > on my linux gateway to provide internet access for the local net.
> > This has been working fine in general, but I have some problems
> > with internet multiplayer in certain games that I believe are due
> > to the IP-masqing.  My ISP provides public addresses via DHCP, but
> > I prefer having static addresses on the local net.  I was wondering
> > if I could use both public & private addresses via IP Aliasing.
> > 
> > Would this work?
> > 
> >           Internet
> >              |
> >              |
> > Gateway |- eth0 public dynamic address
> >         |- eth1:0 bridged with eth0
> >         |- eth1:1 private static address
> >               |
> > Local Net |- eth0:0 public dynamic address
> >           |- eth0:1 private static address
> > 
> Whether this would work or not depends on one detail that you were too 
> vague about. Do you have two public addresses or only one? That is, do > you 
> want Local Net:eth0:0 to have the *same* IP address as Gateway:eth0 or > a 
> different address?
> 
> If they need to be the same address, then I do not know how to do it
> and 
> suspect that there is no way to do it.
> 
> If they are different, the only piece that is not obvious is how to 
> get the 
> dynamic-public address assigned to the Local Net host. Normally, DHCP 
> queries and replies do not cross routers, so you need a DHCP proxy 
> running 
> on the Gateway. There is such an application for Linux, called 
> dhcp-relay 
> ... your distro's packaging system probably has it.
> 
> You also have to get the routing table on Local Net right, so it knows 
> which interface/IP address to use for which traffic. And you probably > have 
> to proxy-arp the Local Net dynamic address on Gateway, since yuor ISP > will 
> not know that its public IP address is their route to the Local Net 
> host. 
> (Your bridging approach may take care of that ... I haven't done 
> bridging 
> recently enough to remember the details ... but I suspect that proxy 
> arp 
> will prove easier to implement.)
> 
> Finally ... games do have problems with standard NAT; they often 
> require 
> port forwarding to work. Also, sometimes the clients need to be told 
> the 
> external IP address through their configuration menus (this is 
> something of 
> a nuisance when dynamic addresses change). Depending on the specific 
> games 
> you are concerned with, you might find it easier to implement port 
> forwarding for them.

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Re: Public & private IP addresses via IP Aliasing?

[Ray Olszewski]

At 09:46 PM 9/19/2003 +0000, beolach@juno.com wrote:

>Thanks, Ray.  Dhcp-relay is exactly what I wanted to know about.
>Unfortunatly, some of the machines on the local network are
>running M$ Windows, which from googling I learn lacks real IP
>Aliasing support - you can get multiple static IPs, but not
>static & DHCP at the same time.  So at least for the windows
>boxes, I will probably switch to DHCP only.

Yeah, that's a problem. Though I use Windows as well as Linux, I'm not 
really all that expert in Windows configuration, so I was only really 
addressing the Linux parts of your problem.

>Which brings up a
>new question: is there an easy way to change the IP address a
>hostname refers to when the machine's IP address changes.  For
>example, the host named gamebox crashes, and after reboot has a
>different IP than before.  Is there a nice way to tell all the
>other computers on the local net that gamebox's address has
>changed?

How do they know it in the first place? The answer to this governs how easy 
it is to change. Possibilities are (I'm giving Linux approaches, but I know 
there are Windows analogs to all of them):

1. A local /etc/hosts file on each machine. In this case, there is no sane 
way to do what you want.

2. A DNS server that is authoritative for the LAN. In this case, the fact 
that the DHCP assignment comes from a different host (the ISP) make it 
tough, as the DNS host itself will not receive the lease info for other 
hosts. The only workaround I can think of for that is that DHCP clients 
typically include a way to run an arbitrary script or program whenever the 
address changes. You could write a pair of scripts -- one on each DHCP host 
that sends a message to the DNS server to update info, the other on the DNS 
server to receive the information and use it to update the DNS records. 
(This is just a scaled-down version of what services that provide 
authoritative DNS resolution for hosts with dynamic addresses do.)

3. SMB shares. This information is provided to the SMB server by the host 
and should be updated whenever an address changes. I've never had a problem 
with that, other than a modest bit of latency.

>I'm guessing that with how common DHCP is, there must
>be a way, but I don't know what it would be.

Actually, to my knowledge, there is no GOOD way to keep DNS-assigned 
hostnames stable when the IP address changes. I hope someone else here 
knows of one and chimes in, as I've had to work around this limitation 
myself from time to time.



[old stuff deleted]

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correlating module names and config options

[John Aspinall]

I'm building my first kernels from sources, and I'm comparing the result 
with the kernel as shipped with typical major distro.  The 
"distro-kernel" is loaded with every possible option built as a module. 
  (Not at all surprising, since they need to install on all kinds of 
hardware.)  But this brings up the following question:

I run lsmod in my distro-kernel to find the modules I actually need on 
this particular hardware.  But how do I establish the relationship 
between the module name, and the configuration option I should choose 
when doing 'make config' or 'make xconfig'?  The correspondence is not 
always obvious.

John

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Re: correlating module names and config options

[Ken Moffat]

On Wed, 15 Oct 2003, John Aspinall wrote:

> I'm building my first kernels from sources, and I'm comparing the result
> with the kernel as shipped with typical major distro.  The
> "distro-kernel" is loaded with every possible option built as a module.
>   (Not at all surprising, since they need to install on all kinds of
> hardware.)  But this brings up the following question:
>
> I run lsmod in my distro-kernel to find the modules I actually need on
> this particular hardware.  But how do I establish the relationship
> between the module name, and the configuration option I should choose
> when doing 'make config' or 'make xconfig'?  The correspondence is not
> always obvious.
>
> John
>

 Have a look at Documentation/Configure.help in your source tree. If
you're using `less' you can search with the `/' key, then scroll up to
read the lines above the module name where the configure option is
listed.

 It's probably also worth looking at what options are nearby in this
file, to try to get pointers to where you can actually find the option
in menuconfig or xconfig.

HTH

Ken
-- 
Will code payroll for food.



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