eBGP & iBGP help

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Dear Expert,

PFA My NW diagram with proposed link.

We are using three ISPs bandwith with eBGP, we have our own IP address and ASN.

Now we are going to start another site with different location with same ASN.

Router A NW IP : 102.21.20.0/22 advertised with Three ISP

Router A (ASN ) 23456

Router B NW IP 102.21.22.0/24  advertised with another ISP in different location with same ASN.

Router B (ASN) 23456

When another ISP b/w goes down then i need my all the traffic going via iBGP (Router A).

My Requirement when link goes down between Router – B to another ISP (Proposed) then my all the traffic working via iBGP.

So what configuration in my both the Router A & B to fulfill my requirement.

Thanks in ADV,

[Pedro Lereno · Accepted solution]

Hi,

You can advertise the route 102.21.22.0/24 on router A with aspath prepend:

router bgp 23456

neighbor outside route-map BGP_ out

route-map BGP_OUT permit 10

match ip address 1

set as-path prepend 23456

route-map BGP_OUT permit 20

access-list 1 permit 102.21.20.0 0.0.0.255

An alternative way would be to use bgp communities to influence ISP local preference (rfc 1998), check this video http://youtu.be/xVQlYPWOCYE

Best Regards,

Pedro Lereno

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Hi Pedro,

Thanks for your great support, but i am confuse b'coz i am not bgp expert so that' why.

can you pl make exact config for both the routers A & B to achieve this.

Great help if u make it.

Once again Thanks in ADV,

[Pedro Lereno · Accepted solution]

Hi,

I think this is what you need to add to your configs:

ROUTER A:

router bgp 23456

network 102.21.22.0 mask 255.255.255.0

neighbor ip_ebgp_nei remote-as 46720          (or 9659 or 28201)

neighbor ip_ebgp_nei route-map BGP_ out

neighbor ip_router_B remote-as 23456

neighbor ip_router_B next-hop-self   ### Check if you mey need this ??

route-map BGP_OUT permit 10

match ip address 1

set as-path prepend 23456 23456

route-map BGP_OUT permit 20

access-list 1 permit 102.21.20.0 0.0.0.255

ROUTER B:

router bgp 23456

network 102.21.22.0 mask 255.255.255.0

neighbor ip_ebgp_nei remote-as 10241

neighbor ip_router_A remote-as 23456

neighbor ip_router_A next-hop-self

The purpose is router A advertise route  102.21.22.0 with as-prepending 2 times AS 23456. On the internet we see this net 2 “hops away” on router A then from router B, so will prefer router B connection.

Recently I have uploaded this video that can help you for as path prepending: http://youtu.be/DVT1y1oSLUs.

If you need more help, send me actual configuration of router A.

I hope this helps!

Best regards,

Pedro Lereno

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Dear Pedro,

Thanks for your great help.

I'll config when i get downtime and get back to u shortly...

If any concern i'll revert you.