Re: >>Two XPs can't see each other<<
From: Bob Willard (BobwBSGS_at_TrashThis.comcast.net)
Date: 02/21/04
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Date: Sat, 21 Feb 2004 10:43:25 -0500
Wayne B. wrote:
> I've been told that a router would be needed for ICS.
> Since I have a switch linking these systems together, I
> figured that I wouldn't be able to get that done until I
> purchased one.
> Everything that you detailed out for me is pretty much
> how I had it understood. (Guess I didn't fall asleep as
> much as I thought I did during classes)
>
> I guess my only foggy point is, is >DNS< as well as
> APIPA default services that run on 98, Win2k and XP? I
> ask that because, lets say for instance, if you put a LAN
> together without any of the machines touching the
> internet, IPs are still distributed out (via APIPA) to
> each machine that requests an IP. But, is name resolution
> present from the beginning (which is what I believe) or
> does it have to be installed and ran? I'm not sure on
> that because there is not one time that I remember
> installing DNS on my machines.
> Thanx Again, Wayne B.
>
>
>>Here's what typically happens (simplified quite a bit):
>>
>>First event: you (or somebody acting for you, such as
>
> the vendor who
>
>>installed XP) gave your PC a name. Second event: an
>
> IPA was given
>
>>to your PC, either by you assigning a static IPA, or by
>
> your PC's
>
>>asking and being given an IPA by a DHCP server, or by
>
> your PC's giving
>
>>itself an APIPA after a failed attempt to get an IPA
>
> from a DHCP
>
>>server. Third event: your PC registers itself with a
>
> DNS server by
>
>>announcing its name and IPA. Note that the DNS server
>
> and the DHCP
>
>>server are software entities which may or may not reside
>
> on the same
>
>>hunk of hardware. Also note that events 1-3 happen for
>
> each PC.
>
>>Fourth event: when you command your source PC to
>
> communicate with
>
>>a target PC (by, say, PING PC123) on your LAN, your
>
> source PC sends
>
>>a request to the DNS server to translate the target PC's
>
> name (PC123)
>
>>into the IPA for that PC; if translation succeeds, then
>
> the source PC
>
>>uses the IPA of the target PC as the target for packets
>
> sent over the
>
>>network (your LAN, in the case of interest).
>>
>>I assume that your XP PRO PC is a gateway to the
>
> internet for your
>
>>other PCs, and that your LAN is controlled by ICS (with
>
> the XP PRO PC as
>
>>the ICS host and the other PCs as ICS clients). If
>
> that's true, then
>
>>that ICS host is the DHCP server and the (real or
>
> virtual) DNS server.
>
>>ICS is hard-wired to use 192.168.x.y for its LAN. Also,
>
> your XP PRO PC
>
>>has a separate IPA to use on its WAN-side, which it gets
>
> by a similar
>
>>process (usually DHCP) from your dial-up ISP.
>>
>>Caveat: The details of address assignment and address
>
> translation
>
>>vary a lot, depending on the protocol(s) used. If you
>
> want to really
>
>>understand how it works, a good starting point is
>
> Cisco's handbook:
>
>>http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/
>
> index.htm
>
>>--
>>Cheers, Bob
>>
>>.
>>
1. DHCP uses a central server to hand out IPAs; each DHCP client
asks the DHCP server for an IPA. OTOH, APIPA does not (I think)
use a central server; rather, each PC selects an IPA on its own,
in the APIPA (169.254.x.y) range. I don't know what algorithm the
APIPA code uses to avoid duplicate assignments on a LAN. APIPA
is independent of ICS.
2. The specific name resolution mechanism used depends on the network
protocols used. You'll need to do a lot of digging to find out how
it really works with the protocols you use, if you really care, and
I suggest starting with the Cisco handbook previously mentioned.
A key point I tried to make in my earlier reply was that DNS and
DHCP are totally separate and, in fact, need not be on the same
hardware; it is rather common to have DHCP in a (hardware or
software) router at your premises, while DNS begins in some box
at the ISP's premises.
3. There are two general types of routing: software routing, and
hardware routing. ICS is an example of software routing; routers
are, clearly, hardware routing. SOHOs almost never need both --
if you have a hardware router, you should in most cases turn off
ICS, since hardware routing is more reliable than ICS (because the
hardware used in a router is dedicated, while ICS shares its PC
with the OS and jillions of apps).
-- Cheers, Bob
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- In reply to: Wayne B.: "Re: >>Two XPs can't see each other<<"
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