Re: Can't Access Printer!!!

gmark <gmark@xxxxxxx> wrote:

On Jul 15, 12:10 am, J.J. O'Shea <try.not...@xxxxxxxxxxx> wrote:
DHCP is fairly simple. A DHCP server automatically assigns IP addresses
to nodes (printers, computers, etc.) attached to it, by Ethernet or by
wireless. These addresses are assigned from out of the DHCP pool.
Private networks,

So the DHCP server (one of the computers always, or could it be in the
router?)

It is usually the router, but it can be a computer running DHCP server
software (rare unless you are running a "server" operating system, or
have specially set it up).

keeps track of the IP addresses it assigns a device?

The DHCP server knows what addresses it has already allocated, so the
next time something asks for an address, it will allocate a new address.

There is an expiry mechanism - typically the addresses are allocated by
the DHCP server for a period such as 24 hours, and the clients
(computers) have to renew their lease of the address before the timer
expires. (The server tells the client how long it has the address for,
and client normally renews the lease when half the time has passed.)

And the device also remembers this.

When a client starts up it will typically remember its previously
assigned address. If so, it asks the DHCP server for permission to reuse
that address. If that address has already been assigned to something
else, the client then asks for a new address and forgets the previously
used one.

If I were you I'd exclude a block of IPs from the DHCP pool generated by
your

This is done via the subnet mask?

No. The subnet mask specifies the pattern for addresses which are
regarded as being part of the same network.

A DHCP server usually has a separate setting which specifies the first
address to be allocated, and the number of consecutive addresses.

For example, a network using 192.168.0.x addressing would have a subnet
mask of 255.255.255.0. If the router is 192.168.0.1 it might be
configured to allocated DHCP addresses starting at 192.168.0.50, for a
maximum of 200 addresses (finishing with 192.168.0.249). That leaves
192.168.0.1 through 192.168.0.49 free for manually assigned addresses
(and also 192.168.0.250 through 192.168.0.254).

All devices on this network would use a subnet mask of 255.255.255.0 and
a gateway/router address of 192.168.0.1.

Netgear, and assign one IP to theprinter, but would let the Netgear hand out
IPs using DHCP to all your computers.

Any reason not to used fixed IPs for the computers?

Ease of configuration. You can leave the computers set up to use the
DHCP server and not have to type in a bunch of numbers to use the
network. Very handy for a laptop or any other computer which gets moved
around to other networks.

The main advantage of using a fixed IP address is if you want to run
some kind of server application on the computer (such as a web server)
and set up a port forwarding rule in your router so that the outside
world can access that server.

It generally isn't necessary for simple operations like file sharing
within the network.

Seems if I wanted to communicate with them, I'd like them to be static so
I could remember them. Or do people generally use symbolic addresses (e.
g., <computer-name>.local ) ?

With Macs, you generally don't need to know the IP address. Bonjour
takes care of advertising computer names and IP addresses, so you can
see shared computers by name in the sidebar of Finder windows (for
example) without having to know what IP address they are using.

Windows has a similar mechanism. I rarely need to know the IP address of
Windows PCs at work.

NAT is also fairly simple. What it does is it uses your router so that your
entire local network pretends to be just one IP on the Internet. The router
has a WAN IP (in your case, 24.15.121.159) and is set up as a gateway using

Where did that IP address (24.15.121.159) come from? The standards
docs?

Your ISP. That is a globally unique IP address. It might be statically
assigned to you by your ISP, or dynamically allocated from a large pool
of IP addresses they use for their customers.

the address 192.168.0.1 on your local net. Any device which is on the
local net and which knows the address of the gateway can use the gateway
to connect to the Internet. The Internet sees only the gateway. You
could have all 254 nodes of a Class C private network set up behind the
gateway, and the only evidence that might point that way would be the
traffic going in and out of the gateway. The router knows which local
device made which request, so it

Where is the data to identify the request a particular packet is
associated with?
Somewhere in the header?

Each UDP or TCP packet header contains a source address, source port
number, destination address and destination port number. These uniquely
identify the connection.

NAT works by changing the source address and port as the packet passes
through your router from your network and out to the Internet. The
router has a table in its memory which remembers the mapping it used,
and when a reply packet comes in from the Internet which is part of the
same connection (matching IP addresses and ports, just swapped over),
the table entry is used to find the appropriate values to pass on to the
originating computer, which is done by modifying the destination IP
address and port.

It seems to me that one of the computers on my network should be
providing the DHCP functionality and is turned off. (Or perhaps the router
used to provide this?)

Probably the router, but if your computers are using DHCP (as clients),
i.e. you haven't manually configured each computer with a static IP
address, then the DHCP server in the router is probably working fine.

Now, if the laser printer used to request a DHCP assignment, it may
also have been disabled inadvertently.

That's possible. My HP LaserJet is connected to my network via a
JetDirect interface, and its default configuration is to not use DHCP.

--
David Empson
dempson@xxxxxxxxxxxxx
.

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