From: Divin Mathew John (divinjohn@gmail.com)
Date: Sun Mar 29 2009 - 19:09:11 ART
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
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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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