telnet on local LAN question

[Tim]

Tim:
>> Partially...  Remember that he had two subnets (192.168.10 and
>> 192.168.2)

Paul Allen Newell:
> Not certain if this is correct ... but I might not be understanding what 
> you mean by two subnets.
> 
> I have up to found Linux boxes ... static 192.168.2.{10,11,12,13}
> 
> I have a Linksys WRT54GL (192.168.2.3) that 3 of the Linux boxes are 
> wired into. That WRT is connected to a larger net which eventually has 
> Verizon out to internet. I am localizing the tests to only run on two of 
> the Linux boxes which are wired into that WRT to minimize "points of 
> failure". I would consider my testbed to be a single subnet ... am I 
> mistaken?

Well, your original post had two sets of IPs mentioned:

  192.168.10.x  and 192.168.2.y

Did a typo creep in, so they should have all started with 192.168.2 and
only the last quad was unique for each device?

NB:  Each part of a IPv4 address, either side of the dots, is nicknamed
a quad.  Since there's four sections to the address (quad <--> four).

If not a typo, then 192.168.10.0 to 192.168.10.255 is a separate network
than 192.168.2.0 to 192.168.2.255, when using the default 255.255.255.0
netmark.  It sets a boundary that says when any of the first three quads
(192 and 168 and 2) are the same, all the IPs denoted by the last quad
are on the same network.  But, if any of the first three quads differ,
then the IPs are on a separate network, and a gateway is required
between them (it's called a gateway as the traffic goes through it to
get to the other side).

See the attached subnets.png file, if it makes it to the list, for a
diagram.  The connect-the-boxes lines show the devices that can directly
talk to each other.  To talk to something else, it has to go through all
the devices in between them (determined by gateway addresses, to say
where; and subnet masks, to work out when it has to go through a
gateway, and when it can go directly).  The diagram has two subnets, one
on the left side, the other on the right.

Most home LANs are a single subnet.  But can be broken into multiple
networks by design or accident.  Such as when someone uses a wireless
access point between one part of the house and another, and the access
point acts as a NAT box, separating all the computers behind it from
those in front of it.  Some people don't realise it breaks the network
up, others have done that purposely.

> FQDNs ???

Fully qualified domain names, as opposed to shortened hostnames.

A hostname could be "fred", and your computer will append the default
domain name (the domain name for the network it's currently on).

A fully qualified domain name could be "fred.example.com.", and that's
the entire domain name.  NB:  The trailing dot is actually part of the
address, it means that that's the top of the tree.  Usually it's not
seen, as there's a presumption that addresses written with one or more
dots in them (example.com or www.example.com) are FQDNs, and the dot
will be presumed to be there (at the end).  In some cases, it's better
to put it in there, explicitly, so nothing tries to add a domain name to
what it might think is just a hostname (e.g. fred.accounting might
really be fred.accounting.example.com).  In other cases, it's required
to put it there, such as in domain name records, else
fred.accounting /will/ be seen as just a hostname that /needs/ a domain
added to it.

You'll find out about that fun if you start playing with mail and DNS
records, properly.  Rather than dabbling with software which makes
guesses for you, usually getting it right, sometimes getting it wrong.


> What do I need to clear up?

Probably, in this instance, exact examples of the names and IPs that
you're trying to use.

> I do want to reiterate that your understanding of my using telnet is 
> right. My eventual target is mail, but telnet seems like a much easier 
> testing target to get the basics down in regard to learning what I need to.

Telnet is a good tool for testing other services.  You can see if a
connection succeeds, and issue manually typed commands to the server.

-- 
[tim at localhost ~]$ uname -r
2.6.27.25-78.2.56.fc9.i686

Don't send private replies to my address, the mailbox is ignored.  I
read messages from the public lists.


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