Velocity Reviews - Computer Hardware Reviews

Velocity Reviews > Newsgroups > Computing > Cisco > when should i turn off ip subnet-zero ?

Reply
Thread Tools

when should i turn off ip subnet-zero ?

 
 
jh3ang
Guest
Posts: n/a
 
      08-02-2006
Hi ? I'm wondering when or in what particular reason should i tun off
ip subnet-zero ?

I saw this statement:
"ip subnet-zero //if router only has its subnet, it should not be used,
so disable ip subnet zero"

please tell me.. what does it mean ?
is there any occasion to turn it off ?

 
Reply With Quote
 
 
 
 
Walter Roberson
Guest
Posts: n/a
 
      08-02-2006
In article <(E-Mail Removed) .com>,
jh3ang <(E-Mail Removed)> wrote:
>Hi ? I'm wondering when or in what particular reason should i tun off
>ip subnet-zero ?


If you aren't running Sun 3 systems, you probably don't need to
leave subnet 0 reserved.

There used to be a reservation of the first subnet within a network,
for use in broadcasting, because at the time either the first or last
address in a range could be used as the broadcast address. The
use of the first address as the broadcast address went away a long
time ago, but Cisco equipment still reserves it in case you are
running old equipment.
 
Reply With Quote
 
 
 
 
Nandan
Guest
Posts: n/a
 
      08-03-2006

Hi There,

When you subnet a major network, you will get multiple subnets. e.g. If
you subnet 192.168.1.0/24 into /26 subnets, then you will get following
four subnets:
192.168.1.0/26
192.168.1.64/26
192.168.1.128/26
192.168.1.192/26

If you turn off ip subnet-zero, then you will NOT be able to use subnet
zero (in this case 192.168.1.0/26). I have always used ip subnet-zero
command, and it has never created a problem for me. So I would never
recommend anyone to turn it off.

Hope this helps.

Best Regards
Nandan

 
Reply With Quote
 
Walter Roberson
Guest
Posts: n/a
 
      08-03-2006
In article <(E-Mail Removed) .com>,
Nandan <(E-Mail Removed)> wrote:

>If you turn off ip subnet-zero, then you will NOT be able to use subnet
>zero (in this case 192.168.1.0/26).


Correct [in the context I snipped]

>I have always used ip subnet-zero
>command, and it has never created a problem for me.


Okay, fine, a valid observation of your personal experience.

>So I would never
>recommend anyone to turn it off.


But that statement tends to indicate that you do not understand
why ip subnet-zero was invented. If you knew -why- subnet zero was
not normally usable, then you would not say that you would "never"
recommend that anyone would turn it off, because some day you may
encounter a network that relies upon subnet zero being reserved.
 
Reply With Quote
 
Barry Margolin
Guest
Posts: n/a
 
      08-04-2006
In article <EKpAg.307255$iF6.70537@pd7tw2no>,
http://www.velocityreviews.com/forums/(E-Mail Removed) (Walter Roberson) wrote:

> In article <(E-Mail Removed) .com>,
> Nandan <(E-Mail Removed)> wrote:
> >So I would never
> >recommend anyone to turn it off.

>
> But that statement tends to indicate that you do not understand
> why ip subnet-zero was invented. If you knew -why- subnet zero was
> not normally usable, then you would not say that you would "never"
> recommend that anyone would turn it off, because some day you may
> encounter a network that relies upon subnet zero being reserved.


It was invented because of issues that existed over a decade ago, and
are now obsolete. Unless you go into a shop that is still running
10-year-old systems, you can safely forget about it. Unfortunately,
Cisco is really slow at changing their default configuration settings.

In other words, knowledge of this is about as useful as knowing how to
administer Windows 3.x systems.

--
Barry Margolin, (E-Mail Removed)
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
 
Reply With Quote
 
Walter Roberson
Guest
Posts: n/a
 
      08-04-2006
In article <(E-Mail Removed)>,
Barry Margolin <(E-Mail Removed)> wrote:

[ip subnet-zero]

>It was invented because of issues that existed over a decade ago, and
>are now obsolete. Unless you go into a shop that is still running
>10-year-old systems, you can safely forget about it.


Yup. Now turn the logic around: If you were to happen to go to a shop
running old systems (or which couldn't afford to change after
having run those systems for a long time), then you would need to
know the command, and in those circumstances you would recommend
its use.

The poster I was replying to was saying that he would *never*
recommend use of the command. He might never encounter those legacy
systems (outside of a cisco cert exam ) but if he -does-
happen to encounter them, how is he going to deal with the
situation if he has denied himself use of the appropriate tool?
 
Reply With Quote
 
Barry Margolin
Guest
Posts: n/a
 
      08-04-2006
In article <soAAg.316247$IK3.306214@pd7tw1no>,
(E-Mail Removed) (Walter Roberson) wrote:

> The poster I was replying to was saying that he would *never*
> recommend use of the command.


And of course on the Internet, every word must be taken absolutely
literally.

--
Barry Margolin, (E-Mail Removed)
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
 
Reply With Quote
 
Walter Roberson
Guest
Posts: n/a
 
      08-06-2006
In article <(E-Mail Removed)>,
Barry Margolin <(E-Mail Removed)> wrote:
>In article <soAAg.316247$IK3.306214@pd7tw1no>,
> (E-Mail Removed) (Walter Roberson) wrote:


>> The poster I was replying to was saying that he would *never*
>> recommend use of the command.


>And of course on the Internet, every word must be taken absolutely
>literally.


On a technical newsgroup, when giving technical advice to others,
"I would never" conveys a very different message than "I have never".

 
Reply With Quote
 
Barry Margolin
Guest
Posts: n/a
 
      08-07-2006
In article <DzoBg.323042$iF6.118216@pd7tw2no>,
(E-Mail Removed) (Walter Roberson) wrote:

> In article <(E-Mail Removed)>,
> Barry Margolin <(E-Mail Removed)> wrote:
> >In article <soAAg.316247$IK3.306214@pd7tw1no>,
> > (E-Mail Removed) (Walter Roberson) wrote:

>
> >> The poster I was replying to was saying that he would *never*
> >> recommend use of the command.

>
> >And of course on the Internet, every word must be taken absolutely
> >literally.

>
> On a technical newsgroup, when giving technical advice to others,
> "I would never" conveys a very different message than "I have never".


I was referring to interpreting "never" as a literal absolute. Like if
someone were to say "I would never kill someone", although in fact there
are most likely some extreme situations where they actually would. Or,
if you want a technical example, one might say "Never just cut power to
a computer, you should always perform a graceful shutdown"; the
qualification that this only applies when a graceful shutdown is
possible is obvious.

--
Barry Margolin, (E-Mail Removed)
Arlington, MA
*** PLEASE post questions in newsgroups, not directly to me ***
*** PLEASE don't copy me on replies, I'll read them in the group ***
 
Reply With Quote
 
 
 
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Viewstate wont turn off even after setting it to off ! robert112 ASP .Net 1 04-26-2007 01:51 AM
How to give users rights to turn their wireless cards on and off =?Utf-8?B?RGVhbg==?= Wireless Networking 1 10-17-2005 10:04 PM
Turn off notification of connection to wireless network =?Utf-8?B?TWljaGFlbA==?= Wireless Networking 1 04-17-2005 11:51 PM
How to turn off "Auto Complete" maradcliff@UNLISTED.com Firefox 1 12-09-2004 04:57 AM
Possible to turn off flowed text? : : b r i a n : : Firefox 2 12-21-2003 07:53 PM



Advertisments