basic networking queries

basic networking queries

[James Miller]

I've set up a small home network and managed to get a few computer talking on
it, including an old laptop.  The laptop prompts this query.  So, I have a
basic grasp of some Linux networking concepts, as well as general networking
concepts.  I set up the home network with static addressing, which seemed
more approachable to me.  Now, I'm going to need to tweak the laptop a bit so
I can use it at some larger institutions (schools) where I visit or study.
Almost surely these places will be using DHCP for assigning network addresses,
and they will likely expect computers hooking up there to be DHCP-capable.
Well, I'm sure I have such capability on the laptop, so that much is in place.
I've also gotten some information from the PCMCIA how to, as well as some
other sources, on ways to select between DHCP and static addressing setups.
In this initial inquiry, I just want to ask for some further information on
how DHCP works, so I'll have an idea what to expect.  Let me pose my questions
as follows: in the network.opts file, which is where rc.pcmcia gets its
information about the network from, there are various entries - ip address,
gateway address, subnet address, network address and the like.  I have at least
a general idea of which of these fields I must fill in on my static, home
network, as well as the values that go there.  What I'm not sure about when
using DHCP is which of the fields (if any) need to be filled in?  Apart from
enabling DHCP there (by entering a "y" in the appropriate field), which other
fields might I need to fill in?  Do I need to know anything about the network
addressing scheme where I'll be using the laptop, or will DHCP take care of
detecting and utilizing all those values?

Depending on the enlightenment or confusion that results from answers I may
receive to this query, I may need to pose additional questions.  Thanks for
your help.

James

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Re: basic networking queries

[Ray Olszewski]

James -- I cannot answer your question directly, because you have provided 
a bit too little information about your setup, and some of what you did 
provide is unusual relative to my experience.

First off, what Linux distribution and version are you using? I'm guessing 
Slackware, but that is no more than a guess (based on the filename 
rc.pcmcia ... of the major distros, I think Slackware is the only one that 
still uses rc* filenames for init scripts).

To get an IP address assigned by DHCP, a system needs to run a DHCP client. 
The one most commonly used, these days, is pump. Others include dhcpcd and 
dhclient. You need to see which of these you have on your system, then 
create or activate an init script that starts one of them with appropriate 
settings. If you have none of them, you need to see which of them your 
distro provides and install one of them ... also maybe create an init 
script, or maybe the install will cause an init script to be installed too.

Or maybe changing the settings in network.opts as you guessed will work, if 
the needed daemon is on your system. It's hard to say. The form of init 
scripts is a bit distro dependent (very much so as regards Slackware), so 
without seeing the script in question, it is hard to be definite about what 
you should do. Usually, if you are using DHCP, you do not fill in fields 
for IP address, netmask, broadcast address, gateway, and maybe nameservers.

Since you are a beginner, I'll close with a bit of beginner advice: 
whenever you pose a question about Linux, here or on any list, always 
mention what distro you are using, what version, and (usually) what kernel 
version (e.g., "Red Hat 9.0 with kernel 2.4.20" or "Debian Sid with kernel 
2.4.19"). It saves everyone a lot of time.

At 08:57 PM 7/24/2003 -0500, James Miller wrote:
>I've set up a small home network and managed to get a few computer talking on
>it, including an old laptop.  The laptop prompts this query.  So, I have a
>basic grasp of some Linux networking concepts, as well as general networking
>concepts.  I set up the home network with static addressing, which seemed
>more approachable to me.  Now, I'm going to need to tweak the laptop a bit so
>I can use it at some larger institutions (schools) where I visit or study.
>Almost surely these places will be using DHCP for assigning network addresses,
>and they will likely expect computers hooking up there to be DHCP-capable.
>Well, I'm sure I have such capability on the laptop, so that much is in place.
>I've also gotten some information from the PCMCIA how to, as well as some
>other sources, on ways to select between DHCP and static addressing setups.
>In this initial inquiry, I just want to ask for some further information on
>how DHCP works, so I'll have an idea what to expect.  Let me pose my questions
>as follows: in the network.opts file, which is where rc.pcmcia gets its
>information about the network from, there are various entries - ip address,
>gateway address, subnet address, network address and the like.  I have at 
>least
>a general idea of which of these fields I must fill in on my static, home
>network, as well as the values that go there.  What I'm not sure about when
>using DHCP is which of the fields (if any) need to be filled in?  Apart from
>enabling DHCP there (by entering a "y" in the appropriate field), which other
>fields might I need to fill in?  Do I need to know anything about the network
>addressing scheme where I'll be using the laptop, or will DHCP take care of
>detecting and utilizing all those values?
>
>Depending on the enlightenment or confusion that results from answers I may
>receive to this query, I may need to pose additional questions.  Thanks for
>your help.




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Re: basic networking queries

[James Miller]

On Thu, 24 Jul 2003, Ray Olszewski wrote:

Thanks for your answer, Ray.  I didn't provide much detail because, rather
than trying to set something up specifically or trying to troubleshoot, I
was trying to understand better *in theory* something about networking -
namely about how DHCP works.  I know so little about it, in fact, that I'm
not sure what sort of information to provide.  I do use a Slackware
variant.  As I mentioned, I know from sources connected with this variant
that some form of dhcp is enabled on it (dhcpd?) and maybe just runs as a
background process.  But this is really already further than I want to go
with this.  I'm just trying to better my grasp on some of the fundamentals
of how dhcp works, what sort of info it needs/uses and the like.  One of
those touchy-feely inquiries, you know, where you're not even sure which
questions to ask to get started learning?  I don't know, maybe you already
know everything about everything and don't find yourself in those sorts of
situations.  But I sure do (not ashamed of admitting it, either).  Anyway,
this sort of inquiry goes in stages for me: I start with some probings,
which helps me get bearings and know what further to ask, where further to
look.  At some later stage of the learning process, I can then formulate
more specific questions related to some task.  But I'm just not at that
stage yet with DHCP.  Is a linux-newbie list not the place to make those
sorts of inquiries?

James

PS I had some problems getting that message to the list, since my initial
post got lost.  Maybe I didn't formulate things very clearly in the
rewriting, with the disappointment of having lost what I'd earlier
started.
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BLOODY CVS

[John T. Williams]

Anyone who has CVS admin experience,
    I'm trying to figure out how to cause files that are added to a CVS rep
to belong to a particular group.  by this I mean, when a user says"

cvs -d:ext:user@mycvs.server:/cvsroot/myproject add newname

user is a member of group myproject (though its not his/her primary group)

I want new file to be added as newfile,v belonging to user.myproject

instead the new files is added as newfile,v belonging to user.(user's
primary group)

which means that I need to manually change the group before other users in
the group can either download file or upload changes to the file.

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Re: basic networking queries

[James Miller]

Ok.  More on DHCP, networking fundamentals, PCMCIA cards and so forth.
The system ref'd is a Slackware 7.1 minimal install on a 486 laptop.  I
will use it most of the time at home, where I have static network
addressing.  The card works, and the machine is successfully on my network
now.  When I need to take it away from home, though, different network
settings will need to be used - almost surely DHCP will be in use where
I'll use it away from home.  I believe what I have on this machine is
udhcpc - some sort of trimmed-down dhcp client.  I have no idea if this is
something I need to start manually, or whether it sort of runs as some
kind of background process (ps axu |more shows no trace of it but, as I
mentioned, I use static addressing on my home network, so I wouldn't
necessarily expect it to be visible).  Now, where to start?  As I
understand it (from the PCMCIA how to), I set my networking options in
/etc/pcmcia/network.opts.  When I run /etc/rc.d/rc.pcmcia start , values
are read from that file to get the network connection up.  I did edit that
file for my home network, and it does get me connected.  But, the question
remains: how to handle those times when I am away from home and may need
to make the card connect to a DHCP network?  What I found relevant to
this in the PCMCIA how to is something called "schemes" that enable one to
have alternate network settings for the PCMCIA card.  Here's an excerpt:

---------------BEGIN EXCERPT----------------------------------
This is fairly easy using ``scheme'' support. Use two configuration
schemes, called ``home'' and ``work''. Here is an example of a
network.opts script with scheme-specific settings:

case "$ADDRESS" in
work,*,*,*)
    # definitions for network card in work scheme
    ...
    ;;
home,*,*,*|default,*,*,*)
    # definitions for network card in home scheme
    ...
    ;;
esac

The first part of a device address is always the configuration scheme. In
this example, the second ``case'' clause will select for both the ``home''
and ``default'' schemes. So, if the scheme is unset for any reason, it
will default to the ``home'' setup.

Now, to select between the two sets of settings, run either:

cardctl scheme home

or

cardctl scheme work
-----------------------END EXCERPT--------------------------------------

Well, I got confused right off.  My network.opts file doesn't look very
similar to this: it consists of about 15 more lines with all kind of
fields where values can be entered in - one of the fields saying something
like 'DHCP=""' - a "y" or "n" needing to follow.  I don't see how I could
use the lines given in the PCMCIA how to: they don't even have a DHCP
option.  I decided that, what I should probably do is simply copy the
whole scheme that appeared in the default network.opts file so that the
file would contain 2 instances of it, then rename the 2 with appropriate
"scheme" entries and edit them accordingly.  This I did.  Was I right?
The "home" scheme contains various static networking entries: the address
of the PCMCIA interface, the gateway's address, etc., and an "n" next to
the DHCP option.  In the "away" scheme (as I called the second scheme),
all fields I left blank except the one next to DHCP, which of course has a
"y".  Does this sound right?  I'm not entirely sure how to go about
testing this, except to take the laptop to a place where I'll use it that
has DHCP and run the cardctl scheme away command from the command line.
One thing that's got me confused is that I tried running the cardctl
scheme away command on my network at home, expecting that I wouldn't get a
working network connection: however, it did connect to the LAN and I was
able to use the 'net connection.  I use Freesco router to route the 'net
connection and LAN traffic and, so far as I know, I've disabled DHCP on
it.  So, why was I able to get on the LAN with the DHCP scheme?  ifconfig
shows that, on the home network, regardless of whether the "home" or
"away" schemes are chosen, eth0 is getting assigned the same address.

Input on this anyone?  I hope it's more comprehensible to someone reading
it than it was to me while writing it: I think I'm still a bit lost.

James

On Thu, 24 Jul 2003, James Miller wrote:

> On Thu, 24 Jul 2003, Ray Olszewski wrote:
>
> Thanks for your answer, Ray.  I didn't provide much detail because, rather
> than trying to set something up specifically or trying to troubleshoot, I
> was trying to understand better *in theory* something about networking -
> namely about how DHCP works.  I know so little about it, in fact, that I'm
> not sure what sort of information to provide.  I do use a Slackware
> variant.  As I mentioned, I know from sources connected with this variant
> that some form of dhcp is enabled on it (dhcpd?) and maybe just runs as a
> background process.  But this is really already further than I want to go
> with this.  I'm just trying to better my grasp on some of the fundamentals
> of how dhcp works, what sort of info it needs/uses and the like.  One of
> those touchy-feely inquiries, you know, where you're not even sure which
> questions to ask to get started learning?  I don't know, maybe you already
> know everything about everything and don't find yourself in those sorts of
> situations.  But I sure do (not ashamed of admitting it, either).  Anyway,
> this sort of inquiry goes in stages for me: I start with some probings,
> which helps me get bearings and know what further to ask, where further to
> look.  At some later stage of the learning process, I can then formulate
> more specific questions related to some task.  But I'm just not at that
> stage yet with DHCP.  Is a linux-newbie list not the place to make those
> sorts of inquiries?
>
> James
>
> PS I had some problems getting that message to the list, since my initial
> post got lost.  Maybe I didn't formulate things very clearly in the
> rewriting, with the disappointment of having lost what I'd earlier
> started.
> -
> To unsubscribe from this list: send the line "unsubscribe linux-newbie" in
> the body of a message to majordomo@vger.kernel.org
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> Please read the FAQ at http://www.linux-learn.org/faqs
>
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Re: basic networking queries

[Jeff Woods]

James Miller wrote:
>I will use it most of the time at home, where I have static network 
>addressing.  The card works, and the machine is successfully on my network 
>now.  When I need to take it away from home, though, different network 
>settings will need to be used - almost surely DHCP will be in use where 
>I'll use it away from home.
>
>But, the question remains: how to handle those times when I am away from 
>home and may need to make the card connect to a DHCP network?  What I 
>found relevant to this in the PCMCIA how to is something called "schemes" 
>that enable one to have alternate network settings for the PCMCIA card.

Rather than trying to change the network configuration manually between 
your home/static and elsewhere/DHCP environments, I recommend you simply 
always use DHCP for the laptop.  Using DHCP at home does *not* mean you 
must use DHCP to assign network information to all your home systems, 
though you probably can if you like.  You can reserve part of your IP 
addresses for static systems and part for dynamic/DHCP systems.

In particular, servers should have static addresses so they don't move 
around, but desktop/workstation/portable systems can usually be dynamic 
without any difficulties.  In fact, due to the auto-configuring aspect of 
DHCP clients and the ability thereby to prevent duplicate IP addresses, it 
makes a lot of sense to me to use DHCP for *all* systems that don't 
*require* static addresses, (i.e. servers).

So you "simply"  ;) configure a DHCP server on some local system at home 
(Mine is built into the DSL router I use.) and then leave the laptop 
enabled for DHCP all the time.  When home, it gets all the network config 
from the home network just like it does when away from home.

--
Jeff Woods <kazrak+kernel@cesmail.net>


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Re: basic networking queries

[James Miller]

Well, this will likely be my final installment on this DHCP issue and the
PCMCIA "schemes" I wrote about earlier.  I have gotten a certain
arrangement to work, though I'm not sure how and why it works.  I suppose
this is a little better than not having it work and not knowing why it
won't work, so I shouldn't complain too much.  And, the workings of it all
may dawn on me as time passes - if senility doesn't set in first, that is.
It turns out that the "solution" (i.e., the procedure that allows me to
use my old laptop on either my home, statically-addressed LAN, or on a
larger DHCP network) is simple.  I don't need any alternate "schemes" or
anything like that.  I just boot the thing like normal, let the init
scripts (I think that's what they're called) assign my home network values
to the PCMCIA NIC interface and all that.  If I'm at home, all is well and
good and off I go onto my network.  If I'm away, I simply issue from the
command line "dhcp," and all the necessary network settings are found and
assigned to the NIC (or wherever they get stored), overriding the static
values I assigned there for the home network.  And away I go onto
that network.  All the while, I sit there stymied, wondering how I can
cram any further information on networking and DHCP into my head.
Clarifications on why this works, what may have been my misperceptions (as
long as these don't involve statements like "that's what u get fer
thinking u were smart enough to use Linux!") etc, are, as always, welcome.

James
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Documentation for int 0x80

[dante]

Hi,

Does anyone know of any good documentation for writing assembly level 
system calls on i386 arch?  I'd like to see something with lots of 
examples.

Anthony G. Basile
Directory of Information Technology
D'Youville College
Buffalo NY, 14201
(716) 881-8197



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Re: basic networking queries

[beolach]

I for one applaud you wanting a deeper understanding of the
underlying protocol, rather than just wanting a quick-fix.
This is one of my favorite aspects of linux; you learn so
much more about how something actually works when you set it
up, very much unlike, say, M$ Windows.

I myself don't have a very deep understanding of how DHCP
works (I have to admit, the few times I ever used it I just
went for the quick-fix), but I think I can point you to some
documentation that you might find interesting.  First off,
you should definitely read the DHCP-mini-HOWTO, available on
The Linux Documentation Project at
<http://www.tldp.org/HOWTO/DHCP/index.html>. It should also
be on your local machine in the /usr/doc/Linux-mini-HOWTOs
directory (Slackware specific). The DHCP-mini-HOWTO mostly
focuses on specific configurations, but it is still a good
read, and in its very small section on the DHCP protocol it
points us to the second document I would recommend, a DHCP
FAQ by John Wobus. But rather than the broken link in the
HOWTO, you can find the FAQ online at
<http://www.mark-itt.ru/Collection/FAQ/dhcp.faq.html>.
Lastly, if you really want to get to the low-down nitty-
gritties, read the Request For Comments (RFC) 2131 and 1541
available at <http://www.ietf.org/rfc/rfc2131.txt> and
<http://www.ietf.org/rfc/rfc1541.txt> respectively.

That's probably enough reading to last you for a while, and
after reading it all, you can be the linux-newbie list expert
on DHCP.  :)

Conway S. Smith

--- James Miller <jamtat@mailsnare.net> wrote:
> 
> Thanks for your answer, Ray.  I didn't provide much detail
> because, rather than trying to set something up specifically
> or trying to troubleshoot, I was trying to understand better
> *in theory* something about networking - namely about how DHCP
> works.  I know so little about it, in fact, that I'm not sure
> what sort of information to provide.  I do use a Slackware
> variant.  As I mentioned, I know from sources connected with
> this variant that some form of dhcp is enabled on it (dhcpd?)
> and maybe just runs as a background process.  But this is really
> already further than I want to go with this.  I'm just trying to
> better my grasp on some of the fundamentals of how dhcp works,
> what sort of info it needs/uses and the like.  One of those
> touchy-feely inquiries, you know, where you're not even sure
> which questions to ask to get started learning?  I don't know,
> maybe you already know everything about everything and don't
> find yourself in those sorts of situations.  But I sure do
> (not ashamed of admitting it, either).  Anyway, this sort of
> inquiry goes in stages for me: I start with some probings,
> which helps me get bearings and know what further to ask, where
> further to look.  At some later stage of the learning process,
> I can then formulate more specific questions related to some task.
> But I'm just not at that stage yet with DHCP.  Is a linux-newbie
> list not the place to make those sorts of inquiries?
> 
> James
> 
> PS I had some problems getting that message to the list, since
> my initial post got lost.  Maybe I didn't formulate things very
> clearly in the rewriting, with the disappointment of having lost
> what I'd earlier started.
> -
> To unsubscribe from this list: send the line "unsubscribe
> linux-newbie" in the body of a message to
> majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.linux-learn.org/faqs


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