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AC 07-18-2003 05:00 PM

Subnetting
 
Set up the scenario a little here:

We have a /23 network coming in through a Cisco router. At the moment, our
Linux box is using proxy arp and has the network divided into two pieces. I
want to elimate proxy arp and use the Linux box as a proper router.
Basically I want to take our /23 and cut it into two /24s.

I'm pretty sure I can do the configuration on the Linux box, but the Cisco
box has me a little confused. I think it might be as simple as the IOS
command:

ip route y.y.y.y 255.255.255.0 x.x.x.21

(where y is the upper /24 and x is the lower /24).

Is this right, or am I missing something?

--
Aaron Clausen

maureen-taocow-ng1@alberni.net

Barry Margolin 07-18-2003 05:05 PM

Re: Subnetting
 
In article <slrnbhga1q.214.maureen-taocow-ng1@ts1.alberni.net>,
AC <maureen-taocow-ng1@alberni.net> wrote:
>Set up the scenario a little here:
>
>We have a /23 network coming in through a Cisco router. At the moment, our
>Linux box is using proxy arp and has the network divided into two pieces. I
>want to elimate proxy arp and use the Linux box as a proper router.
>Basically I want to take our /23 and cut it into two /24s.
>
>I'm pretty sure I can do the configuration on the Linux box, but the Cisco
>box has me a little confused. I think it might be as simple as the IOS
>command:
>
>ip route y.y.y.y 255.255.255.0 x.x.x.21
>
>(where y is the upper /24 and x is the lower /24).
>
>Is this right, or am I missing something?


You're right.

--
Barry Margolin, barry.margolin@level3.com
Level(3), Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

AC 07-18-2003 08:09 PM

Re: Subnetting
 
On Fri, 18 Jul 2003 17:05:04 GMT,
Barry Margolin <barry.margolin@level3.com> wrote:
> In article <slrnbhga1q.214.maureen-taocow-ng1@ts1.alberni.net>,
> AC <maureen-taocow-ng1@alberni.net> wrote:
>>Set up the scenario a little here:
>>
>>We have a /23 network coming in through a Cisco router. At the moment, our
>>Linux box is using proxy arp and has the network divided into two pieces. I
>>want to elimate proxy arp and use the Linux box as a proper router.
>>Basically I want to take our /23 and cut it into two /24s.
>>
>>I'm pretty sure I can do the configuration on the Linux box, but the Cisco
>>box has me a little confused. I think it might be as simple as the IOS
>>command:
>>
>>ip route y.y.y.y 255.255.255.0 x.x.x.21
>>
>>(where y is the upper /24 and x is the lower /24).
>>
>>Is this right, or am I missing something?

>
> You're right.


I'm glad I'm right about something. Let's try a more tangible example.

We've got a /23:

10.101.104.0/23

Ethernet1 on the cisco unit has the following configuration:

interface Ethernet1
ip address 10.101.104.0 255.255.254.0
no ip directed-broadcast

To forward the upper /24 to the Linux router, the entry is:

ip route 10.101.105.0 255.255.255.0 10.101.104.2

(Where 10.101.104.2 is the Linux router's address on the lower /24)

It's that simple from the Cisco box?

--
Aaron Clausen

maureen-taocow-ng1@alberni.net

Barry Margolin 07-18-2003 08:14 PM

Re: Subnetting
 
In article <slrnbhgl3h.6gi.maureen-taocow-ng1@ts1.alberni.net>,
AC <maureen-taocow-ng1@alberni.net> wrote:
>I'm glad I'm right about something. Let's try a more tangible example.
>
>We've got a /23:
>
>10.101.104.0/23
>
>Ethernet1 on the cisco unit has the following configuration:
>
>interface Ethernet1
> ip address 10.101.104.0 255.255.254.0
> no ip directed-broadcast
>
>To forward the upper /24 to the Linux router, the entry is:
>
>ip route 10.101.105.0 255.255.255.0 10.101.104.2
>
>(Where 10.101.104.2 is the Linux router's address on the lower /24)
>
>It's that simple from the Cisco box?


Yes. You would also normally change the subnet mask in the "ip address"
statement to 255.255.255.0.

--
Barry Margolin, barry.margolin@level3.com
Level(3), Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

AC 07-18-2003 08:33 PM

Re: Subnetting
 
On Fri, 18 Jul 2003 20:14:16 GMT,
Barry Margolin <barry.margolin@level3.com> wrote:
> In article <slrnbhgl3h.6gi.maureen-taocow-ng1@ts1.alberni.net>,
> AC <maureen-taocow-ng1@alberni.net> wrote:
>>I'm glad I'm right about something. Let's try a more tangible example.
>>
>>We've got a /23:
>>
>>10.101.104.0/23
>>
>>Ethernet1 on the cisco unit has the following configuration:
>>
>>interface Ethernet1
>> ip address 10.101.104.0 255.255.254.0
>> no ip directed-broadcast
>>
>>To forward the upper /24 to the Linux router, the entry is:
>>
>>ip route 10.101.105.0 255.255.255.0 10.101.104.2
>>
>>(Where 10.101.104.2 is the Linux router's address on the lower /24)
>>
>>It's that simple from the Cisco box?

>
> Yes. You would also normally change the subnet mask in the "ip address"
> statement to 255.255.255.0.


So the Ethernet1 config would like this?

interface Ethernet1
ip address 10.101.104.0 255.255.255.0
no ip directed-broadcast

--
Aaron Clausen

maureen-taocow-ng1@alberni.net

Barry Margolin 07-18-2003 09:39 PM

Re: Subnetting
 
In article <slrnbhgmgi.7a4.maureen-taocow-ng1@ts1.alberni.net>,
AC <maureen-taocow-ng1@alberni.net> wrote:
>On Fri, 18 Jul 2003 20:14:16 GMT,
>Barry Margolin <barry.margolin@level3.com> wrote:
>> Yes. You would also normally change the subnet mask in the "ip address"
>> statement to 255.255.255.0.

>
>So the Ethernet1 config would like this?
>
>interface Ethernet1
> ip address 10.101.104.0 255.255.255.0
> no ip directed-broadcast


Actually, the address needs to be in the range 10.101.104.1 through
10.101.104.254. .0 is the network address and .255 is the broadcast
address.

--
Barry Margolin, barry.margolin@level3.com
Level(3), Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

AC 07-21-2003 05:40 PM

Re: Subnetting
 
On Fri, 18 Jul 2003 21:39:36 GMT,
Barry Margolin <barry.margolin@level3.com> wrote:
> In article <slrnbhgmgi.7a4.maureen-taocow-ng1@ts1.alberni.net>,
> AC <maureen-taocow-ng1@alberni.net> wrote:
>>On Fri, 18 Jul 2003 20:14:16 GMT,
>>Barry Margolin <barry.margolin@level3.com> wrote:
>>> Yes. You would also normally change the subnet mask in the "ip address"
>>> statement to 255.255.255.0.

>>
>>So the Ethernet1 config would like this?
>>
>>interface Ethernet1
>> ip address 10.101.104.0 255.255.255.0
>> no ip directed-broadcast

>
> Actually, the address needs to be in the range 10.101.104.1 through
> 10.101.104.254. .0 is the network address and .255 is the broadcast
> address.


Okay. Can you give me an example of how the Interface commands should look?
Sorry to be a pain, but I feel like I'm missing something here.

--
Aaron Clausen

maureen-taocow-ng1@alberni.net

Barry Margolin 07-21-2003 05:57 PM

Re: Subnetting
 
In article <slrnbho9i0.ejl.maureen-taocow-ng1@ts1.alberni.net>,
AC <maureen-taocow-ng1@alberni.net> wrote:
>On Fri, 18 Jul 2003 21:39:36 GMT,
>Barry Margolin <barry.margolin@level3.com> wrote:
>> In article <slrnbhgmgi.7a4.maureen-taocow-ng1@ts1.alberni.net>,
>> AC <maureen-taocow-ng1@alberni.net> wrote:
>>>On Fri, 18 Jul 2003 20:14:16 GMT,
>>>Barry Margolin <barry.margolin@level3.com> wrote:
>>>> Yes. You would also normally change the subnet mask in the "ip address"
>>>> statement to 255.255.255.0.
>>>
>>>So the Ethernet1 config would like this?
>>>
>>>interface Ethernet1
>>> ip address 10.101.104.0 255.255.255.0
>>> no ip directed-broadcast

>>
>> Actually, the address needs to be in the range 10.101.104.1 through
>> 10.101.104.254. .0 is the network address and .255 is the broadcast
>> address.

>
>Okay. Can you give me an example of how the Interface commands should look?
>Sorry to be a pain, but I feel like I'm missing something here.


interface Ethernet1
ip address 10.101.104.1 255.255.255.0

--
Barry Margolin, barry.margolin@level3.com
Level(3), Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.

AC 07-21-2003 06:00 PM

Re: Subnetting
 
On Mon, 21 Jul 2003 17:57:47 GMT,
Barry Margolin <barry.margolin@level3.com> wrote:
> In article <slrnbho9i0.ejl.maureen-taocow-ng1@ts1.alberni.net>,
> AC <maureen-taocow-ng1@alberni.net> wrote:
>>On Fri, 18 Jul 2003 21:39:36 GMT,
>>Barry Margolin <barry.margolin@level3.com> wrote:
>>> In article <slrnbhgmgi.7a4.maureen-taocow-ng1@ts1.alberni.net>,
>>> AC <maureen-taocow-ng1@alberni.net> wrote:
>>>>On Fri, 18 Jul 2003 20:14:16 GMT,
>>>>Barry Margolin <barry.margolin@level3.com> wrote:
>>>>> Yes. You would also normally change the subnet mask in the "ip address"
>>>>> statement to 255.255.255.0.
>>>>
>>>>So the Ethernet1 config would like this?
>>>>
>>>>interface Ethernet1
>>>> ip address 10.101.104.0 255.255.255.0
>>>> no ip directed-broadcast
>>>
>>> Actually, the address needs to be in the range 10.101.104.1 through
>>> 10.101.104.254. .0 is the network address and .255 is the broadcast
>>> address.

>>
>>Okay. Can you give me an example of how the Interface commands should look?
>>Sorry to be a pain, but I feel like I'm missing something here.

>
> interface Ethernet1
> ip address 10.101.104.1 255.255.255.0


Why do I suddenly feel like an idiot?

Thanks for the help.

--
Aaron Clausen

maureen-taocow-ng1@alberni.net


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