BGP config WAS RE: [c-nsp] internet redundancy [7:99340]

[David Barak]

in-line.

--- Vikas Sharma <vikassharmas at gmail.com> wrote:

> Hi,
>  1) You don't need to pay for using ASN as this is
> default BGP attribute.

the fact than an ASN is a default attribute has
nothing whatsoever to do with payment.  In any case,
Tom will need to contact a RIR (ARIN, RIPE, etc) and
obtain a public ASN, and for this, he'll have to pay a
nominal annual fee.


> 2) It is better if u use IBGP internally because
> IBGP support all attribute 
> of BGP and one should avoid redistribution as
> possible.
> 3) You need your ASN only when u want to differ from
> ISP policies otherwise 
> u don't require ASN.

Tom is connecting to multiple ISPs - therefore, BGP is
the appropriate solution.  


> 4) To filter you can use 
>  a) Prefix filtering
>  b) AS_path filtering
>  c) Route map fltering
>  d) Community filtering

The most effective type of filtering in this case is
done on the provider's routers - just ask the provider
for their networks and their customer networks, and
all will be well.  

>  beside this u need to ask ur SP's to broadcast
> other SP's route in their 
> network or u may not need this if BGP
> synchronization is enable in all SPs.

No service provider worth their salt uses BGP
synchronization.  If they did, they would only
advertise routes which appeared in their IGP!  Rather,
if Tom's ISPs are all cooperative, then they will
permit him to originate address space, and will carry
those announcements rather than aggregating them.  

>  Chad :- here internet router and core router are
> different. so no need to 
> think abt internet link go down as these are
> seperate router. Redistribution 
> of default route is a good option with network
> 0.0.0.0 <http://0.0.0.0> in 
> bgp, but if that link is down there will not be any
> connectivity. You can 
> also use MED attribute to specify the best route.

ick!  Redistribution of a default route is an ugly
solution: the better approach is to have the edge
routers all speak iBGP with each other and the core
routers which make decisions.  The core routers are
the default gateways for Tom's internal network, and
once data reaches the core, it follows a BGP path
outward.


-David Barak


David Barak
Need Geek Rock?  Try The Franchise: 
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