Re: prefix advertisement in bpg

No, it will be using a null route so that it can advertise a summary route
such as the /16 in your example.

The null route is used so that when a packet arrives it checks to see if there
is a route matching the destination that is more specific than the /16 null
route, if there isn't then the null route is used and the traffic is dropped.

Regards

David Rothera
CCIE #38338
Sent from my iPhone
Please excuse any mistakes and brevity.

On 15 Apr 2013, at 08:16, Imran Ali <immrccie_at_gmail.com> wrote:

> so far i did not see any logical reason to point it to null 0 ,
>
> in case servers are using private ip, and they do nat to translate public
block to private block . but since this public subnet is non existant we need
a route for nat to work,
>
> is my mind correct ?
>
>
> On Mon, Apr 15, 2013 at 9:40 AM, David Rothera <david.rothera_at_gmail.com>
wrote:
>> It doesn't have to be in an IGP (unless you are using IGP sync) but simply
the routing table itself, either by a static route or from an IGP.
>>
>> Regards
>>
>> David Rothera
>> CCIE #38338
>> Sent from my iPhone
>> Please excuse any mistakes and brevity.
>>
>> On 15 Apr 2013, at 06:14, Ahmed Hussain <engine10_at_gmail.com> wrote:
>>
>> > Before BGP can advertise the prefix it has to be in IGP. thats what the
>> > null route is doing.
>> >
>> >
>> > On Fri, Apr 12, 2013 at 10:01 PM, Imran Ali <immrccie_at_gmail.com> wrote:
>> >
>> >> why some bgp implementations adds a null route for advertised
prefixes
>> >>
>> >> ex
>> >>
>> >> router bgp 2
>> >> bgp log-neighbor-changes
>> >> network 128.16.16.0 mask 255.255.255.0
>> >> network 130.130.0.0
>> >> neighbor 10.10.10.1 remote-as 1 * neighbor 10.10.10.1 advertise-map
>> >> ADVERTISE non-exist-map NON-EXIST***neighbor 10.10.20.3 remote-as 3
>> >> !
>> >> ip route 130.130.0.0 255.255.0.0 *Null0*
>> >>
>> >>
>> >>
>> >> is has something to do with NAT ?
>> >>
>> >>
>> >> Blogs and organic groups at http://www.ccie.net
>> >>
>> >> _______________________________________________________________________
>> >> Subscription information may be found at:
>> >> http://www.groupstudy.com/list/CCIELab.html
>> >
>> >
>> > Blogs and organic groups at http://www.ccie.net
>> >
>> > _______________________________________________________________________
>> > Subscription information may be found at:
>> > http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Mon Apr 15 2013 - 08:42:25 ART