[nsp] bgp - aggregates and specific routes

[Roger]

joshua sahala wrote:

>>A customer of ours, who's range is say 192.168.16.0/24 will be using our 
>>numbers and advertising said route to other eBGP peers.
>>    
>>
>
> your numbers?
>
>  
>
Yes - the 192.168.16.0/24 falls within the 192.168.0.0/19 range.  This 
was mentioned in the previous post.  The /24 is downstream from us and 
they're getting their own ASN. 

In real life we have a /19 delgated to us by ARIN.

> how are you learning the /24?  if you are learning it from your
> customer, then when the link goes down, you will stop learning that
> prefix and will subsequently stop advertising it.  if you are
> learning it via some other means, then i'd need to know how that is
> to answer this.
>  
>
We are learning the /24 via eBGP.  Now if the eBGP session between us 
and said downstream customer(16.0/24) goes down connectivity to the 
16.0/24 will still occur because it will be lumped in w/ our 
aggregate...  We need to prevent this when the eBGP session goes down. 


> /24 is more specific than /19, so for addresses in that /24, traffic
> will go towards your customers other providers.  all other traffic
> for the /19 will come to you
>
>  
>
I disagree.  While yes the /24 is more specific we are only advertising 
our aggregate /19 to upstream providers.  If the eBGP link between us 
and our downstream customer, using our numbers, goes down  connectivity 
will appear to normal because the /19 is still shown as up.

I'm looking for a route-map statement or some conditional advertisement 
statement.

>>router bgp 1
>>no synchronization
>>bgp log-neighbor-changes
>>network 192.168.0.0 mask 255.255.224.0
>>neighbor 1.2.3.4 remote-as 1234
>>neighbor 1.2.3.4 description WAN Link 1
>>neighbor 1.2.3.4 send-community
>>neighbor 5.6.7.8 remote-as 5678
>>neighbor 5.6.7.8 description WAN Link 2
>>neighbor 5.6.7.8 send-community
>>neighbor 192.168.16.254 remote-as 2
>>neighbor 192.168.16.254 description downstream customer
>>neighbor 192.168.16.254 send-community
>>!
>>ip route 192.168.0.0 255.255.224.0 Null0
>>    
>>
>
>this looks good - make sure that you are using some prefix filters
>and/or as path filters to prevent readvertising prefixes that you do
>not want to provide transit for ;-)
>  
>

No - the problem is we WANT to be a transit AS for our downstream 
customer 16.0/24 only if a eBGP link between us and them is in working 
order.  I'll continue to look.

I'll look over my original post - I think you missed the point or I 
didn't explain things clearly..

-- 
Rock River Internet                          Roger Grunkemeyer
202 W. State St, 8th Floor                grunky at rockriver.net
Rockford, IL 61101                           815-968-9888 x102