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

[Vikas Sharma]

Hi,
 1) You don't need to pay for using ASN as this is default BGP attribute.
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.
4) To filter you can use 
 a) Prefix filtering
 b) AS_path filtering
 c) Route map fltering
 d) Community filtering
 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.
 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.
 Regards
Vikas
    Date: Wed, 18 May 2005 14:15:58 -0400
From: "Kern, Tom" <tkern at CHARMER.COM>
Subject: BGP config WAS RE: [c-nsp] internet redundancy [7:99340]
To: <cisco at groupstudy.com>, "Cisco List 2 (E-mail)"
<cisco-nsp at puck.nether.net>
Message-ID:
<677F8D88345F3E4AB753BBEC7E7C576DFE084B at EXCHANGE2.CHARMERNYDOM.CSG-IT.NET>

Content-Type: text/plain; charset="iso-8859-1"


Ok, i'm still trying to set up an internet redundancy solution.
I unsucessfully attempted this only using eigrp and tunneling it through my 
firewall and redistributing static routes,etc. But that never worked.
A while back someone mentioned bgp and to get over the FUD surrounding it 
and just try it.

Ok, so now i'm gonna try it.

My senario is probably well known(too well known, everyone on this list 
would say).
I have 3 sites with 3 isps. The 3 sites connect to each other via point o 
point T1's(not the same routers as the internet facing one's).

I want to set up outgoing and incoming redudancy(disregard any resoultion 
issues and ddns soultions for now).

I'm going to use bgp.
My question are as follows-
1.I need to use the ASN of each respective isp, correct? Do they charge for 
this normally?

2. Internally, do I need to run ibgp or should i redistribute ebgp into 
eigrp?

3. If i run ibgp, do i need a "real" ASN or can I use a private one?

4. Aside from setting up an AS-Path filter is there anything else i need to 
do to prevent filling up my routing table with isp routes?

5. Am i missing anything else?


Thanks



Kern, Tom wrote:
> I set up a ebgp link from the 3 routers to the 3 isp's.
> now, do i inject the ebgp stuff into eigrp or do i run ibgp between
> the 3
> internet routers?
>
>
> i'm confused as to when i should redistribute into an IGP or run ibgp
> Thanks a lot
>
> Chad Larsen wrote:
>> Tom,
>>
>> You'll need to setup BGP with the ISP's and have them advertise only
>> default route to you. You should redistribute the default route
>> into EIGRP..this will allow the route to disappear if the internet
>> link goes down. At this point you'll have 3 edge routers
>> advertising a default route...the EIGRP metrics will allow the PC's
>> to make it out the default router that is closest to them (least
>> cost metric).
>> As far as inbound, you need to advertise your IP block out each ISP
>> with BGP and prepend your own as to manipulate which link will be
>> preferred by the net. Also, you will most likely neet to set a bgp
>> community attribute to manipulate the traffic from within the same
>> ISP's cloud (most of the bigger ISP's will have info on which
>> community should be set).
>>
>> Hopefully this helps,
>>
>> -chad
>>