Setup BGP over multiple ISP

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Sep 24th, 2014
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Hello,

I am not well versed in BGP, so please pardon my seeming ignorant questions when you reply.

I have a task at hand to configure BGP on a Cisco 2951 router such that 3 ISPs are connected directly to the router, and the LAN as well.

I am to configure internet load sharing on all 3 links for LAN use. I may have to involve a DMZ somewhere, but this is still in the works. SO what is important for me now is to successfully setup all 3 ISPs on the router, and allow internet traffic to be successfully shared over all 3 links.

I have attached a sketch of what i feel may illustrate this better.

I am also attaching a config that i feel may work, but would need comments where necessary to be sure.

Thank you for your valuab

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Akash Agrawal Wed, 09/24/2014 - 11:16
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Hi,

 

Normally we see high traffic in incoming direction where you may want to load share the traffic. To load share in incoming direction, you need to advertise your prefixes accordingly.

 

In your BGP config, i am seeing just three eBGP neighbors to three ISP, no BGP to internal router. No BGP network origination other than 3 wan ip to ISP and no redistribution. What would be your lan pool and how would you originate it inot BGP.

 

Regards,

Akash

femi.agboade Wed, 09/24/2014 - 16:42
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Hello Akash,

Thank you for your response.

As regards prefix, not sure what you referring to here.

As regards internal router, i assume you are referring to another router that sits between the BGP router and the LAN? If this is so, if you look at my config again, you'll see that the BGP router will be LAN router as well. If you go through the config again, you'll see that interface GE0/0 has been configured with a LAN IP. Is it an advisable/recommended to have a separate router for the LAN?

No BGP network origination and no redistribution; not sure what is implied here. Can you help?

LAN Pool: 192.168.20.0/24

Please note that the config is a proposed one, i would appreciate recommended options to guide me into successfully implementing this correctly.

I appreciate your valuable comments.

 

Regards,

Femi

 

 

Akash Agrawal Wed, 09/24/2014 - 20:38
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Hi Femi,

 

I understand GE0/0 is LAN interface. I just got confused since 192.168.0.0/16 is private ip range and how can we advertise this subnet to ISP for internet use.

 

Regarding load share on different ISP link, in which direction you want to load share traffic outbound or inbound. If it is outbound, you can prefer selective prefixes through one ISP (use of local preference) and selective through other ISP. If it is inbound, then you need to advertise your prefixes accordingly. Now you have /24 lan pool. You can not split it into further subnets since tier-1 ISPs dont accept prefixes smaller than /24. In this case, it would be difficult to load share inbound traffic.

 

Regards,

Akash

femi.agboade Thu, 09/25/2014 - 02:07
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Hello Akash,

Not sure where you got the 192.168.0.0/16 private range from, i think i only had the 192.168.20.0/24 range, which is just for illustration purpose. I am not sure we need to advertise the subnet to ISP since it will be natted in any case when traffic hits the router right?

As regards load sharing, basically what we are trying to achieve is share outbound traffic from within the office on all 3 ISP links and when one fails, all internet bound traffic will be routed only through the other working 2.

I honestly am not sure i understand what your other statements are about, but i will appreciate if you can give samples to work with. i build my config from various samples and similar scenarios to ours.

Thanks again for your valuable feedback.

Regards,

Femi

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