I have a HP Laserjet 1320 (ip, says x.y.z.w). I have two computers: one installed winxp and other is running CentOS somewhere else. Usually, I do the printing job via winxp. For the linux, I use nomachine client, installed in the winxp, to remotely logon it. I want to setup the printer on linux too. First of all, I use Nmap to see what ports are being opened at the printer, it returns

-----------------------------------------------
PORT STATE SERVICE
23/tcp open telnet
80/tcp open http
280/tcp open http-mgmt
515/tcp open printer
9100/tcp filtered jetdirect
-----------------------------------------------

Does anyone know what's the difference b/w the last two lines?

Anyway, in linux, I logon as root, turn off the firewall first. Go to printer settings, new a printer, choose corresponding model and driver, choose [Network Printers (TCP)] -> scan all all possible printers at x.y.z.* at port 9100, it retruns some chooses but I didn't see my printer. So I try to scan x.y.z.* at port 515, this time, it shows my printer. I select that item, now the URI of the printer becomes

URI: socket://x.y.z.w:515

socket??? is that normal?

I don't know if there is anything wrong, but when I test the printing, nothing comes out.

I also try different interfaces. First of all, I try "Remote CUPS server (IPP/HTTP)", but it asks me to input user identification, what kind of information I have to provide? The user information for loggon on the linux?

I also try "Network printer w/IPP (IPP/HTTP)", similarly, I scan the subnetwork x.y.z.* at port 9100 and 515, it shows some items (same as before), buy whatever I click in the list, it freezes there forever and have to shut it down by killing the process in the background! Am I doing
somehting wrong? Anyway, I reopen the printer setting, repeat whatever I did before, but I didn't scan the pinter, I directly input URI as x.y.z.w:9100 or x.y.z.w:515, when I try to print something ...
after a while, some junk was coming out (not what I am printing) while the printing job still stays in the montior forever

So what's the different b/w "Network printer w/IPP (IPP/HTTP)" and "Network Printers (TCP)]"? Which one is the right choice for my case?

I think port 9100 is an LPD port.
which means that it should work ok.
it should be set up to act aas a unix network printer.

first try this: (a.b.c.d is the printer address)

ls | nc a.b.c.d 9100

if it works...
then, open an application (e.g. firefox) and print to file
this will give you a postscript file.
try

cat file.ps | nc a.b.c.d 9100

if this works out fine it's a simple job.
I've had no luck with IPP but with TCP it looks like you should be fine.

try cups

browser to localhost:631 should bring up the admin and
set up your printer as an LPD postscript printer.

Thanks a lot for your reply. ls | nc a.b.c.d 9100 returns nothing,moreover,if I scan the within this section a.b.c.* at 9100, the ip for the printer didn't shown in the return list. It is there only when I scan a.b.c.* at 515, weird !

Anyway, I following what you said to call cups at localhost:631,

1) I add a new printer, choose Location and Description as OurHP1320, Name is HP1320.

2) In next screen, for choosing the Device, I choose "LPD/LPR Host or Printer", but I read the manual for HP1320 series, it has something call JetDirect, so should I chose "AppSocket/HP JetDirect" instead?

3) In next screen, in Device URI, I input socket://a.b.c.d:9100 (I also try socket://a.b.c.d:515 since this is what scan printer over the network return)

4) In next screen, for Make/Manufacturer for HP1320, I choose HP

5) In next screen, for Model/Driver for HP1320, I choose "HP LaserJet 1320 series Postscript (recommended) (en)" but when I click to proceed, it shows "A username and password are being requested by http://localhost:631. The site says: "CUPS", I don't know what that password and user is for, I input one for the root, is that ok?

However, after this setup, it seems still no good to use the network printer. If I choose socket://a.b.c.d:515 instead of 9100, when I print something, the pritner will print a few lines (with cups information included) but that's not what I am printing...

did you try

lpd://printer?

do you mean lpd://a.b.c.d or just lpd://printer ?

I try the first one, but seems not work. I din't know if the later one works or not, but will the system find it if I just give a name "printer"?

lpd://a.b.c.d

I would try just the following without including any port number.
ipp://w.x.y.z