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Home > Archive > Unix administration > March 2006 > When to use a null model cable or adapter?
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When to use a null model cable or adapter?
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| Joe D. 2006-03-03, 6:43 pm |
| Hi all; I am managing an environment with numerous Sun servers, from
old Ultra-XX to V120 and V210 blades, to 280R, 420R, and V880's. Very
few of them have consoles attached. I would like to set up a terminal
server environment to enable console connectivity to them for local and
remote access to console. I am looking for some advice on the 'basics'
I will need; particularly with regard to 'null modem' cabling.
>From my reading thus far, I understand that I will want to connect up
to the Serial A port to ensure that I get POST diags and other boot
messages at boot time and for maintenance. Does the connection to the
Serial port A ALWAYS need to be a null-modem connection, or does it
vary from server to server, and if so, does anyone know a link to a
quick summary of which Sun servers need what? I've been downloading
user and field service guides from Sun, but it would be nice to have
this in a concise tabular format.
Also, can anyone recommend any particular manufacturer of terminal
servers or switches, or whatever that would meet my needs? I'm looking
for capacity of 20 - 25 servers, with the ability for local access
(terminal in the actual computer room) and remote access to the switch,
where I could then select whichever server's port I needed. Are there
adapters available that turn a regular ether cable into a null modem
cable (say, a two piece connector set; one in Serial A, the other on
the Terminal serverport , and they're wired such that all you need do
is connect them with an ether?).
Any pointers, past experiences, tips and gotchas gratefully appreciated
and acknowledged.
Joe
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| Doug McIntyre 2006-03-03, 6:43 pm |
| "Joe D." <newbie_from_newbie@yahoo.com> writes:
>I will need; particularly with regard to 'null modem' cabling.
There's usually a DCE and a DTE. If you have two DCE's, you need a
null modem in the middle to make one end look like a DTE by flipping
transmit and receive, and whatever handshaking lines you are using.
Thus, if you have a computer going to a computer, you'll need a null modem.
>to the Serial A port to ensure that I get POST diags and other boot
>messages at boot time and for maintenance. Does the connection to the
>Serial port A ALWAYS need to be a null-modem connection, or does it
>vary from server to server, and if so, does anyone know a link to a
>quick summary of which Sun servers need what? I've been downloading
>user and field service guides from Sun, but it would be nice to have
>this in a concise tabular format.
No, its pretty consistant, you pretty much need a null-modem
everytime. Unless of course, you have a cable already wired as a null-modem.
Some devices (just like in ethernet) try to trick you out by making
themselves look like DTEs instead of DCEs, and then you need a null
modem on the end of your null modem cable if that is what you are using.
FWIW: Sun followed along with the industry to make serial cables on RJ45
constitant to the cisco standard. One nice feature of the cisco layout
is that if you roll the cable (ie. pin 1 to 8) and plug it in that
way, you have a null modem. Very convienient.
>Also, can anyone recommend any particular manufacturer of terminal
>servers or switches, or whatever that would meet my needs? I'm looking
>for capacity of 20 - 25 servers, with the ability for local access
>(terminal in the actual computer room) and remote access to the switch,
>where I could then select whichever server's port I needed.
Sure, what's your budget? Cyclades makes some nice units. You'd
probably be able to find 4-5 without really looking too hard.
> Are there adapters available that turn a regular ether cable into a
>null modem cable (say, a two piece connector set; one in Serial A,
>the other on the Terminal serverport , and they're wired such that
>all you need do is connect them with an ether?).
Its better to use flat cable instead of twisted pair, but yes, there
are adaptor modules you can buy. Since there aren't many consistant
standards (or, perhaps too many standards that nobody followed one
until recently), they all come unwired, and you are expected to wire
them to whatever standard you want to use.
Or, buy serial cables from your term server vendor at their higher price.
The canonical page to refer to is at..
http://www.sunhelp.org/unix-serial-port-resources/
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| Darren Dunham 2006-03-03, 6:43 pm |
| In comp.unix.solaris Joe D. <newbie_from_newbie@yahoo.com> wrote:
> From my reading thus far, I understand that I will want to connect up
> to the Serial A port to ensure that I get POST diags and other boot
> messages at boot time and for maintenance. Does the connection to the
> Serial port A ALWAYS need to be a null-modem connection, or does it
> vary from server to server, and if so, does anyone know a link to a
> quick summary of which Sun servers need what? I've been downloading
> user and field service guides from Sun, but it would be nice to have
> this in a concise tabular format.
A "straight-through" cable is useful when going from a modem to a
terminal. They're designed for this. However, when going from a
terminal to a terminal, you can't. They both talk on the same pins, so
the cable has to swap them. This is the basic bit of the null-modem.
You need it any time you're attaching two terminal-like (DTE) ports
together. All Sun boxes and PCs will have DTE serial ports.
http://www.sunhelp.org/unix-serial-...serial-pinouts/
Dedicated terminal server hardware may be wired any way they like.
You'd need to refer to their documentation for what is right to do.
--
Darren Dunham ddunham@taos.com
Senior Technical Consultant TAOS http://www.taos.com/
Got some Dr Pepper? San Francisco, CA bay area
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