NFS help (.. is definitely needed)

[Greg Julius]

I broke this up to understand it and reply in parts.

>not wanting to get into a heavy discussion on this issue, I will just state
>this simply.  
>
>My ISP assigns me a IP address, I have a router and through
>the DHCP my computer is assigned a local IP address and since I have
>connected to my local address I have up to 5 local IP addresses(could have
>many more if I liked) under this standard each of the 5 IP addresses are
>translated to go out the one address assigned by the ISP.

This router sounds like a standard router which you can get from Linksys,
NetGear, et. al.  In comes one wire (the WAN from your ISP) and out goes one
or more wires (the LAN).  Many even have an access point built into them to
give wireless capability to the LAN.  These things are quite amazing when
you think about it.  They have multiple Network ports, they accomplish many
networking chores, they provide address translation and some firewall
capabilities and even wireless.  All in a box between $25 and $125.  Easy to
use and easy to set up.  Reliable as the day is long.

<warning>
Discourse on DHCP, WAN, LAN, NAT, and SPI forthcomming, skip if you know all
about it.  But since this thread is turning into a general education on
networking, it feels right to do this.  I hope I'm not insane and showing
too many flaws in my understanding.  Everyone please jump in where I have
boned it up.
</warning>

Most ISPs providing high-speed internet give a dynamic address.  If you are
providing services to the internet (say a web-site or an email server) then
you will probably need a static IP.  There are a few reasons where you might
need one even if you don't provide services to the internet.  Some providers
will only give you static addresses and some providers will never give you a
static address.

In any event, the router has the ability to "speak DHCP" to the ISP and
request an IP from the ISP (they come out of the box configured that way).
They can also be configured to respond to a specific static ip if that is
what your ISP gave you.

Some routers have the ability to report to one of the "dynamic DNS"
providers (like DynDNS JEff mentions) the IP address assigned by the ISP.
This gives the ability for the internet at large to find your router even
though it doesn't have the decency <grin> to stay at a given address.
Static IP assignments don't need the dynamic DNS solutions.

The configuration of the WAN side of the router, either static or dynamic
provides some much needed information:  The network address & subnet, the
router's address as seen from the internet, the router's gateway IP to the
internet, and a couple (usually two or more) Domain Name Servers for Domain
Name resolution.

So, for the sake of this discussion, let's say that the WAN IP address (the
address of the router as seen from the Internet) is A.A.A.34 (make up your
own numbers for A.A.A <grin>  For the literal, the A number is between 0 and
255).  This WAN IP could have been dynamic or static.  The important thing
is that there is one.  There will also be the other values as mentioned
above.

That covers the WAN side.  Now for the LAN side.

The router usually provides DHCP services to the devices attached to the LAN
by wires or wireless.  The router can also accept devices that have a fixed
IP address.

On the LAN side, you would commonly get a set of addresses starting with
192.168.0.x or sometimes 192.168.1.x - I've seen both - if the address were
generated by an out of the box router by DHCP.  x is usually a value
starting at 100 and going up.  Supposing you have two devices attached, then
one could be 192.168.0.100 and another could be 192.168.0.101.  If you
configure the DHCP service provided by the router you can end up with
anything.  Note that the router also has a network address on the LAN,
usually 192.168.0.1.  This is the address of your router as seen from inside
your network.

OK, now we have a wire on the right (The WAN) and wires on the left (The
LAN).  The WAN side of things can be thought of as the Internet.  The LAN
side of things can be thought of as the internal network or Intranet.

>From the point of view of the internet, all of your computers have the same
address, Namely A.A.A.34, the address of the WAN IP on your router.  The
crowd on the internet never sees your internal 192.168.0.x address.

So, how does your computer attached at 192.168.0.100 carry on a
"conversation" with a computer on the internet?  More to the point, how does
a response from something on the internet get to  your PC if all of the PCs
on your internal network appear to have the same address?  That's NAT's job.

NAT is Network Address Translation.  ** Note:  I am about to really simplify
here to avoid confusing on exactly how this works  **  When you start a
"conversation" with an Internet service (say your email at your ISP) your PC
says I want to talk to IP B.B.B.B (which is the IP provided by some DNS
server for the name of your email server on your ISP).  The first thing your
computer does is look up to see where it should send it.  It doesn't know so
it sends it to the gateway for your network.  The gateway will usually be
the router (remember the 192.168.0.1 address from earlier?).

The router then takes note of which computer the message came from and where
it was going (it remembers), it then translates the internal network address
into a variation of the A.A.A.34 address and then sends the message along on
to the next hop which will be the gateway address of the WAN.

When the reply comes back, the router looks up where it came from and where
it was going (the variation of the A.A.A.34), "untranslates" the addresses
and sends the message to the appropriate computer.

That's NAT in a nutshell.

Now what about when somebody sends something to A.A.A.34 out of the blue?
Usually, because it doesn't know who it was intended for (can't find
anything in it's memory about it) it throws it away.  This feature is a part
of what is called SPI (Stateful Packet Inspection).  When you send something
out (an outgoing packet), the router remembers who, what, when, how.  When a
reply comes back (an incoming packet) the who, what, when, and how is
compared to prior outgoing packets looking for a match.  If it doesn't find
it, and the router isn't configured to do something special with it, then it
just throws it away.  This is a basic firewall feature and helps to prevent
uninvited outsiders from getting into your network.

That's SPI in a nutshell.


>When it assigns
>me the one IP address it assigns my IP address to two DNS IP addresses and
>it also assigns a gateway.  

A bit of care here on the terminology.  Your ISP assigned your router a
network address & subnet, an IP, and a gateway and INFORMED it of two DNS
addresses that it could use for retrieving IP addresses from Domain names.
It didn't send anything to the DNS for you.

>The ISP can change the IP address it assigns to
>me(this assignment is a dynamic assignment) anytime it wants and it will be
>transparent to me because the DNS to which this IP is assigned is updated
>with the IP address and since it is transparent somebody in China can still
>send a message or connect to my network and they don't need to have the new
>IP address that is assigned.  

Sigh.  Not exactly right.  Yes, the ISP can, will, and does change the
address which gets assigned to your router.  It does not send anything to
the DNS.  Period.  Your router may send something to a DynDNS type service,
but you can rest assured that your ISP did not.

For clarity, I would like to find out why you think your address is getting
assigned to the DNS so somebody in china can get to you?  

I'm not denying that they can send you messages via email or even via some
instant messanger or something of the sort, but not by the name of your pc
which is inside your internal network.

>Now on my local network I can have the same
>setup.  I can have my own DNS server that I assign my local IP to and it
>resolves the issues for my local network.  On local networks arbitration
>goes on and somebody declares I'm the boss and I will handle all of this
>info and if he drops out then the arbitration happens again and somebody
>else becomes boss, etc etc.  

This sound extremely like NETBIOS processes and is not a function of TCP/IP
at all, nor even of the internet.  Are you sure you are not confusing the
two as they are very similar in purpose and function?

Yes, you can set up a DNS on your internal network.  All it takes is a host
to run it on.  Yes, you can put in your DNS the IP addresses of the machines
on your network.  This is manually done usually.

There are even some routers which now contain am mDNS which works in
conjunction with their internal DHCP and gives a "Dynamic DNS" ability.  The
Dynamic part is the Address assignment from DHCP and a real-time update of
the DNS of that assignment data.  But even in this case, the mDNS is being
updated by the DHCP and not by the host.  I know it sounds like splitting
hairs, but of such is the network made.


The rest of the statement is not DHCP nor DNS and sounds like NETBIOS.

>The DNS declares himself to be the boss of the
>5 computers on my local and does all of the resolutions for my network and
>communicates with the outside world to resolve the issues.

This would definately be NETBIOS. It isn't DNS.  While DNS may give name
resolution services, it doesn't declare itself boss.  The Network setup data
provided by DHCP or by manual configuration says where to go look for name
to address resolution.

>One of the
>issues that you mention is true for domains like .com, .net, and etc. 
???

>but
>that is only part of the answer the other part is the routing and routing
>tables and these are important in the address resolution.

Actually, routing and routing tables have nothing to do with name to address
resolution.  Nor DHCP.

Routing and routing tables are the underlying mechanism for getting a packet
from point Address A.A.A.A to B.B.B.B  This involves a lot of things like
address resolution protocol and transmission metrics and RIPs and such which
I won't even begin to touch.  My understanding of that is shakey at best.

DHCP is the assignment of an internet address (your WAN or LAN addresses for
example) to a particular host or device.  This device may be on your
internal network or perhaps your router address from your ISP.

DNS is concerned with mapping a name (POP.EXAMPLE.COM) to an internet IP
address (the A.A.A.A or B.B.B.B).


>While I don't
>disagree with you completely.  There are definitely holes, I am not a
>expert, but you can check any ISP assignment to see that the structure I
>presented above is alive and working.

Jeff makes excellent points about the internet and shows a keen grasp of the
issues facing dynamic domain name service issues on the internet as a whole.
I think Jeff was thinking mostly about the internet at large in his
response.  LANs have a bit more flexibility and that is where this
discussion originally started.

Regarding your claim that that's how it works, I just don't see it.  I don't
know which part of the internet you are using, but mine doesn't work the way
you describe.  Neither the parts inside my three LANs nor the parts of the
internet I interface with connecting my LANs to the internet and while
providing web hosting to my clients.  I get the feeling you are mixing
NETBIOS and DNS and DHCP and such in a big mash.

>SNMP is a part of what you presented
>so I am not completely positive about all of this but there is chaos going
>on when you decide to send a message, cause a route has to be setup and it
>is this arbitration between the DNS that determine how to setup this route.

I did a search on the original message and don't find SNMP mentioned.
Simple Network Management Protocol is a tool used to manage the devices on
the network and to diagnose the network when it is down or not working
correctly.  I don't really use it yet as my needs have been simple to this
point.  Soon, but not now.

-g