Console vs. Auxiliary

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I get confused between the console port and the auxiliary post on Cisco
routers and switches.

Which is the serial and which is the RJ45 port?

And when would I want to use each one?

Thanks.

--
Andrew W. Young                                  news03@andrew-young.com
                                             http://www.andrew-young.com /

Re: Console vs. Auxiliary
Whether the console and aux ports are RJ45 ports or not depends on the
platform.  The newer platforms tend to be RJ45 ports.

You will mostly use the console port to manage the box by reverse
telnetting to it.  The aux port tends to come into use when you need
remote access to the box via a modem.  Only the aux port can support a
modem connected to it that you can dial into.

Cisco da Gama
http://ciscostudy.blogspot.com


Re: Console vs. Auxiliary

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What do you mean by "reverse telnet" ?  Is this a routine telnet
session, e.g.:

telnet 1.2.3.4 23

What is the console port physically cabled to?

--
Andrew W. Young                                  news03@andrew-young.com
                                             http://www.andrew-young.com /

Re: Console vs. Auxiliary

You can connect a flat, green cable between the console port on your
router and an access port on an access server like the AS-2511RJ. This
is called a "rolled cable" on exams or a "console cable" in real life.

Suppose you connect your console port to port 5 on the access server,
and the access server has ip address 128.0.0.1. You then would use the
command, "telnet 128.0.0.1 2005" to access your router. If you connect
to port 12 on the access server, you would use the command "telnet
128.0.0.1 2012" to access your router. This is called reverse telnet.

You can do the same thing with the auxiliary port, except you need a
flat, pale-blue cable. You can call this an "aux cable" if you like.

Serial connectors... complicate things. I encourage you to check out
this page because it will help on the exam and in the real world:

http://www.cisco.com/en/US/products/hw/routers/ps332/products_tech_note09186a0080094ce6.shtml

Basic cabling is essential knowledge for a network engineer.

On Fri, 17 Feb 2006 20:00:17 +0000, Andrew W Young

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Re: Console vs. Auxiliary

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I wouldn't get attached to those colours, nor the "flatness" of the cable -
this is solely for local identification.

I needed a console cable in a hurry once so made one up from what I had to
hand - white Cat5 UTP.

Aubrey



Re: Console vs. Auxiliary
On Sat, 18 Feb 2006 13:45:24 +0800, "Aubrey Adams"
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Conventions minimize errors and simplify debugging. I wanted to help
the original poster visualize how things should really look.

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That's a good point. In an emergency, mix cables, adaptors, and
extenders as necessary... but re-standardize as soon as possible.

The link I sent earlier explains how to mix those parts.

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Re: Console vs. Auxiliary
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Would you typically leave the console port connected to an access port
on an access server as a permanent installation?  Is it the console port
on a switch or router which has the device's own IP configured rather
than any other interface?

If you don't connect the console port to an access server, can you still
telnet to the router/switch via the production network?

--
Andrew W. Young                                  news03@andrew-young.com
                                             http://www.andrew-young.com /

Re: Console vs. Auxiliary
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Depending on how many routers you have in your network, leaving the
console port connected to a comm-server may not be practical.  With a
few routers is certainly reasonable to have all their console ports
connected to a comm-server for easy manageability.

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You seem to be misunderstanding something here.  The console port does
not have an IP address.  The console port is reached via the IP address
of the comm-server using reverse-telnet explained earlier in this
thread.

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Sure you can.  You just need to make sure that routing is set up fine
so that you can telnet to the router over one of its network
interfaces.

Cisco da Gama
http://ciscostudy.blogspot.com


Re: Console vs. Auxiliary
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I see.  So, in a large infrastructure why would you bother to use an
access server at all?  Why not just telnet direct to each router/switch?


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Ah, understood, thanks.

--
Andrew W. Young                                  news03@andrew-young.com
                                             http://www.andrew-young.com /

Re: Console vs. Auxiliary
On Mon, 20 Feb 2006 10:26:27 +0000, Andrew W Young

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+ Telnet is not an option when you initially configure a device. You
have to use the console port

+ Telnet is not an option for some troubleshooting scenarios--such as
recovering a password.

+ In many network designs, the management network is more reliable
than the production traffic network.

+ Having full remote access limits how much time you spend walking
between devices vs. troubleshooting them

+ When 24/7 uptime of a device is important, 24/7 full remote access
to those same devices is also important.

Re: Console vs. Auxiliary
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That's wonderful -- many thanks for your time answering my questions.

--
Andrew W. Young                                  news03@andrew-young.com
                                             http://www.andrew-young.com /

Re: Console vs. Auxiliary

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It depends. An access server costs $1500 anconnects upto 16 devices.
Ask yourself how important is 24/7 remote access to a device?

For wireless access points and desktop switches, an after-hours outage
can probably wait until the next business day for debugging. However,
a core switch, router, or server outage may require an immediate fix.

A permanent access server means you can debug these problems faster
and usually without spending time travelling to/from the office.

Re: Console vs. Auxiliary
That may be one use, but I wouldn't say that is the usual use. Generally the
console cable is what you'll use to physically connect your notebook to
configure the system or reload. AUX port is also used in conjunction with a
modem for remote sites. You can use those two ports for reverse telnet and
many other access needs.


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Re: Console vs. Auxiliary

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The only real difference is the AUX port uses hardware flow control, where
the CON port has no flow control.



Re: Console vs. Auxiliary
On Fri, 17 Feb 2006 17:00:59 +0000, Andrew W Young wrote:

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someone in here posted that you can't connect a modem to a console port.
yes you can.  I've connected to many a router like this.  the modem will
answer your call, not the router in this case.  use hyperterminal to do
it.  it's been about 5years since i've done it though, but it CAN be done.

Re: Console vs. Auxiliary
That was me saying earlier that the AUX port is usually used to connect
modems to.  I didn't mean to imply that modems could not be connected
to console ports.  Note that though possible, there are several
potential issues to be aware of while connecting modems to console
ports.  Please take a look at

http://www.cisco.com/warp/public/76/9.html#consoleport

Cisco da Gama
http://ciscostudy.blogspot.com


Re: Console vs. Auxiliary
I concur on this point and one huge reason why you would connect a modem to
the console port instead of the aux port is that if you reload the router
the aux port will reset and the modem will drop whereas the console port
stays connected and you can use that to access rommon or watch the boot
process.


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