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jskfan
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Configure BGP

Configure BGP

https://www.experts-exchange.com/questions/29010316/Public-DNS-Vs-BGP.html

following the Thread on the above link, When I purchase Public IP addresse(s), and register the IP addresse(S) with a Public DNS, then how do I configure my router for BGP so that customers will chose ISP1 as most preferred to get to that public IP address and use ISP2 as less preferred

Thank you
RoutersTCP/IP* bgp

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jskfan

8/22/2022 - Mon
Jan Bacher

What router manufacturer?
jskfan

ASKER
That 's Cisco Router
Jan Bacher

This should work:

#############################################

ip prefix-list ANNOUNCE seq 5 192.168.0.0/24
ip prefix-list ANNOUNCE seq 5 192.168.2.0/23 le 24

route-map LOCALPREF permit 10
 set local-preference 500

route-map DEPREFER permit 10
 match ip address ANNOUNCE
 set as-path prepend 65535 65535 65535

router bgp 65535
 neighbor 10.0.0.1 description Primary ISP
 neighbor 10.0.0.1 route-map in LOCALPREF
 neighbor 10.0.0.1 prefix-list ANNOUNCE out
 neighbor 172.16.2.1 description Backup ISP
 neighbor 172.16.2.1 route-map DEPREFER out
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jskfan

ASKER
Thanks Jan Springer,
for Education purposes, can you please comment below each line, just to explain what each line is meant for ?
Jan Bacher

The prefix list defines those subnets that you are announcing to your upstream.

The LOCALPREF route-map assigns a higher local preference for outgoing traffic to your preferred provider.

The DEPREFER route-map prepends your ASN to create a longer and less preferred path.
jskfan

ASKER
in your example
192.168.0.0/24  is the Public IP that is registered on  the public DNS  ?
the same applies to this one 192.168.2.0/23 le 24?
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Jan Bacher

No, that's the subnet that's assigned to you either by one of your providers or your RIR.  

IPs out of that subnet could/would be defined in DNS.

"le 24" means allow me to announce this subnet as one /23 or two /24s.
jskfan

ASKER
Ok Thanks Jan...

What is the key word
OUT
meaning in :
neighbor 10.0.0.1 prefix-list ANNOUNCE out

and

neighbor 172.16.2.1 route-map DEPREFER out

Why not "IN", since customer will try  to get in ?
Jan Bacher

I want to announce these prefixes  going OUT to my neighbor.

How I want to traffic engineer data coming IN to me.

The "why" has to do with logic and how the people that wrote the RFCs determined.
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jskfan

ASKER
I thought since these subnets are already out on the Public DNS
192.168.0.0/24
192.168.2.0/23 le 24

customers will use them to get in
jskfan

ASKER
Jan Springer,

probably if you can comment each line..That might help me understand better the "Morse Code"
Jan Bacher

The purpose of using BGP is to tell your router how you want to reach the outside world and how you want the outside world to reach you.

Again.  You are confusing BGP and DNS.
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jskfan

ASKER
In your example what do these IP addresses represent   ?
192.168.0.0/24
  192.168.2.0/23
 10.0.0.1  
  10.0.0.1
   10.0.0.1  
  172.16.2.1  
 172.16.2.1
jskfan

ASKER
Ok , just to confirm the way they have explained it to me:
My company will have Public IP addresses for my web servers x.x.x.x , y.y.y.y , these addresses Registered in DNS.
I will advertise those IP Subnets  to ISP-A and ISP-B , then on my edge router I can configure, for instance if  a Customer needs access x.x.x.x network then they can come through ISP-A if they need to access y.y.y.y network then they can come through ISP-B



bgp
Jan Bacher

No.

If you can advertise address space via BGP, then you have a /24 or larger.  Those are the IPs that you put on your server and configure in DNS.

The path taken by your customers to reach you will be determined by your traffic engineering (localpref, etc) and their provider traffic engineering.

And it looks like this:

   SomeRemoteIPs => Internet => ProviderA \
                                                                                  => MyCompanyRouter  => Servers
   OtherRemoteIPs => Internet => ProviderB /
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jskfan

ASKER
MyCompany is my Router where BGP is configured.. it will advertize to ISP-A and ISP-B the purchased IP subnets.

Public DNS will have Ip addresses of my web servers..

The path that will be  taken by my customers to reach my web servers will be determined by the configuration of BGP on Mycompany router (as you stated for instance using Local Preference attribute)
jskfan

ASKER
the IP addresses I put on public DNS , will be within the subnets I advertize through BGP
jskfan

ASKER
Correct ?
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ASKER CERTIFIED SOLUTION
Jan Bacher

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jskfan

ASKER
I see what you are saying ...
Was just example in case you purchased 2 or more IP ranges for  2 or more different sites
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jskfan

ASKER
Thank you  Jan Springer