From: Salah ElShekeil (salah.elshekeil@gmail.com)
Date: Sun Mar 29 2009 - 19:11:24 ART
you have to lab it up Raghav you will understand,
if you have questions just ping :)
On Mon, Mar 30, 2009 at 1:09 AM, Divin Mathew John <divinjohn@gmail.com>wrote:
> yeah. salah just put it Small and Simple!
> Thanking You
>
> Yours Sincerely
>
> Divin Mathew John
> divinjohn@gmail.com
> divin@dide3d.com
> +91 9945430983
> +91 9846697191
> +974 5008916
> PGP PUBLIC KEY BLOCK @ http://www.dide3d.com/divin_Public_PGP_key.txt
> Sent from: Bangalore KA India.
>
> On Mon, Mar 30, 2009 at 3:37 AM, Salah ElShekeil <
> salah.elshekeil@gmail.com> wrote:
>
>> if the router who is generating the summary have no longer match in its
>> routing domain then it will discard it
>>
>>
>> On Mon, Mar 30, 2009 at 1:03 AM, Raghav Bhargava <
>> raghavbhargava12@gmail.com> wrote:
>>
>>> Hi divin/salah,
>>>
>>> Can you guys please answer my questions that I requested for in my
>>> mail..I understand in EIGRP wen we create a summary address it creates a
>>> Null 0 route but my question is if a packet comes in for a different network
>>> what happens then..
>>>
>>> raghav
>>>
>>>
>>> On Sun, Mar 29, 2009 at 3:00 PM, Salah ElShekeil <
>>> salah.elshekeil@gmail.com> wrote:
>>>
>>>> yep in rip it won't creat route to Null you have to do it manually
>>>>
>>>> ip route xxxx xxxx null0
>>>>
>>>> On Mon, Mar 30, 2009 at 12:56 AM, Divin Mathew John <
>>>> divinjohn@gmail.com> wrote:
>>>>
>>>>> and i do think its only in OSPF and EIGRP when u do summarize routes
>>>>> internal or external that creates a NULL route automatically.! for rip
>>>>> i
>>>>> guess will have to create a static route pointing to the Null0 with a
>>>>> higher
>>>>> administrative distance than any other routing protocol....to avoid
>>>>> loops/!
>>>>> Thanking You
>>>>>
>>>>> Yours Sincerely
>>>>>
>>>>> Divin Mathew John
>>>>> divinjohn@gmail.com
>>>>> divin@dide3d.com
>>>>> +91 9945430983
>>>>> +91 9846697191
>>>>> +974 5008916
>>>>> PGP PUBLIC KEY BLOCK @ http://www.dide3d.com/divin_Public_PGP_key.txt
>>>>> Sent from: Bangalore KA India.
>>>>>
>>>>> On Mon, Mar 30, 2009 at 3:25 AM, Divin Mathew John <
>>>>> divinjohn@gmail.com>wrote:
>>>>>
>>>>> > The Null interface is typically used for preventing routing loops.
>>>>> Enhanced
>>>>> >> Interior Gateway Routing Protocol (EIGRP), for instance, always
>>>>> creates a
>>>>> >> route to the Null0 interface when it summarizes a group of routes.
>>>>> Whenever
>>>>> >> a routing protocol summarizes, this means that the router might
>>>>> receive
>>>>> >> traffic for any IP address within that summary. Because not all IP
>>>>> addresses
>>>>> >> are always in use, there is a risk of looping packets in case
>>>>> default routes
>>>>> >> are used on the router which receives the traffic for the summary.
>>>>> >
>>>>> >
>>>>> >
>>>>> http://www.cisco.com/en/US/tech/tk364/technologies_tech_note09186a00801c9a6e.shtml
>>>>> > refer that doc. u will know why null0 is created
>>>>> > and
>>>>> >
>>>>> >
>>>>> http://www.cisco.com/en/US/tech/tk364/technologies_tech_note09186a00801c9a6e.shtml
>>>>> >
>>>>> > However, in IOS levels 12.1(6) and higher, this discard route is
>>>>> generated
>>>>> > by default, and you don't need to create it. If you want to disable
>>>>> creation
>>>>> > of the discard route, use the *no discard-route* command:
>>>>> >
>>>>> >> Router1(config)#*router ospf 55*
>>>>> >> Router1(config-router)#*no discard-route internal*
>>>>> >>
>>>>> >>
>>>>> >> Router1(config-router)#*no discard-route external*
>>>>> >>
>>>>> >> With the *internal* keyword, this command prevents the router from
>>>>> > automatically generating discard routes for internal summary routes.
>>>>> > Similarly, the *external *keyword is for external routes. However, we
>>>>> urge
>>>>> > caution with this command because the absence of a discard route can
>>>>> cause
>>>>> > loops.
>>>>> >
>>>>> >
>>>>> >
>>>>> > Thanking You
>>>>> >
>>>>> > Yours Sincerely
>>>>> >
>>>>> > Divin Mathew John
>>>>> > divinjohn@gmail.com
>>>>> > divin@dide3d.com
>>>>> > +91 9945430983
>>>>> > +91 9846697191
>>>>> > +974 5008916
>>>>> > PGP PUBLIC KEY BLOCK @
>>>>> http://www.dide3d.com/divin_Public_PGP_key.txt
>>>>> >
>>>>> >
>>>>> >
>>>>> > On Mon, Mar 30, 2009 at 2:27 AM, Raghav Bhargava <
>>>>> > raghavbhargava12@gmail.com> wrote:
>>>>> >
>>>>> >> Hi Experts,
>>>>> >>
>>>>> >> Have some doubts related to Null 0.
>>>>> >>
>>>>> >> In EIGRP,
>>>>> >>
>>>>> >> For example if we have 4 networks:-
>>>>> >>
>>>>> >> 1.1.0.1/24 , 1.1.1.1/24, 1.1.2.1/24, 1.1.3.1/24
>>>>> >>
>>>>> >> Now lets say I summarise them all under 1 default route by the
>>>>> command ip
>>>>> >> summary -address eigrp 10 0.0.0.0 0.0.0.0
>>>>> >>
>>>>> >> when I do this it creates a Null 0 route in the Routing table. So If
>>>>> I
>>>>> >> would
>>>>> >> have not summarise these networks as a default route and would have
>>>>> done
>>>>> >> it
>>>>> >> like this ip summary-address eigrp 10 1.1.0.0 0.0.3.255 .Then will
>>>>> the
>>>>> >> Null
>>>>> >> 0 route be created.???? I don know..
>>>>> >>
>>>>> >> As per my understanding of Null 0 , it helps in preventing
>>>>> forwarding
>>>>> >> Loops
>>>>> >> . So does it mean that if i want to reach a network which is outside
>>>>> of
>>>>> >> these 4 networks for eg - 4.4.4.4/24. The Null 0 will drop the
>>>>> route for
>>>>> >> this network. Please correct me if I am wrong.
>>>>> >>
>>>>> >> Secondly like in OSPF also when we do summarisation of internal
>>>>> /external
>>>>> >> routes a null 0 route is created. I know it is used for preventing
>>>>> >> forwarding loops but will it do the same thing . I mean if a route
>>>>> for a
>>>>> >> different network comes in will it drop it.
>>>>> >>
>>>>> >> Also in OSPF we can remove this Null 0 via the command---> no
>>>>> >> discard-route
>>>>> >> internal/external. Why do we do that if Null 0 helps in preventing
>>>>> the
>>>>> >> loops.
>>>>> >>
>>>>> >> Last but not the least is there a command to do the same in other
>>>>> >> protocols
>>>>> >> like RIP, EIGRP, BGP.
>>>>> >>
>>>>> >> just curiosu to know ....
>>>>> >>
>>>>> >>
>>>>> >> --
>>>>> >> Warm Regards
>>>>> >> Raghav
>>>>> >>
>>>>> >>
>>>>> >> Blogs and organic groups at http://www.ccie.net
>>>>> >>
>>>>> >>
>>>>> _______________________________________________________________________
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>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>
>>>
>>>
>>> --
>>> Warm Regards
>>> Raghav
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