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Webcast-Catalyst9k
New Member

LoadBalancing to two ISPs

Dear,

I have two ISPs, one is sending me the full BGP router ( ISP-A) while the other one is sending me only the default reoute 0.0.0.0 (ISP-B).

How I can manage and do load balancing to both ISPs?

regards

MHS

12 REPLIES
New Member

LoadBalancing to two ISPs

Hi,

Impossible. If You have only default route from provider B, all traffic will go to existing routes, except illegal traffic without destination. For example, port scanning.

BGP isn't for load balancing, it's for traffic management. You'll need to plan what traffic destination to be sent to which provider. If no, then one provider will be better to almost all the world.

Anyway, You'll need to ask second provider for real routes. It can be full table, or something smaller. For example, Your country inside routes from direct peers between local providers. And also You'll need to ask provider to announce Your routes to these links too. Some providers give possibilities to control outgoing routes through route tags, You can ask provider for it. Some routing paths can be assimetric, but mostly it's better to keep it simetric. Anyway, it will be nat a real balancing.

No one will give You universal recipe for traffic and route management. It's individual an depends from Your providers, Your need, Your possibilities, Your wishes.

Kind Regards,

UgisD.

Re: LoadBalancing to two ISPs

Hi, Have a look at the following BGP configuration guide for load sharing:

http://www.cisco.com/en/US/tech/tk365/technologies_configuration_example09186a00800945bf.shtml

It states that:

"Load balancing is not possible in a multihomed  environment with two ISPs. BGP selects only the single best path to a  destination among the BGP paths that are learned from different AS's,  which makes load balancing impossible. But, load sharing is possible in  such multihomed BGP networks"

New Member

LoadBalancing to two ISPs

Thanks UgisD & Sean,

However, currently most of my traffic 95 % is going through the ISP-A which advertise the full BGP routing and very less traffic through the ISP-B which advertise the defautl route.

Is it there a way to manage the traffic to both ISPs in such away? or I have to ask one ISP-B to send the full BGP routes or ISP-A to send the defualt route only.

Which is better for traffic managment to have two defualt routes or the full BGP routes?

regards

MHS

New Member

Re: LoadBalancing to two ISPs

Got to the same issue.

The following options were implemented:

1.) ISP-b run full routing (best if it's 1st tier ISP)

2.) ISP-b should get you a new /24 block and advertise it on both providers

3.) start using the ISP-b IP block for web services

It did help the traffic but not much. ISP-b just a third tier ISP and not so many customers.

New Member

Re: LoadBalancing to two ISPs

Dear Eli,

Could you pelase clarify point (2 & 3).

2- I have my own subnet /20 I am advertiving the full subnet /20 to both ISP and also hlaf subnet to ISP-A and another half to ISP-B.

3- Can you clarifiy it more.

Thnx

MHS

Re: LoadBalancing to two ISPs

Hi Alshamlan,

If there is not any special reason to get the full internet routing table by your ISP, to request them to send you a default route.

It will be much easier to troubleshoot, to load share and you will save much CPU and Memory from your routers.

Hope that helps,

Vasilis

New Member

Re: LoadBalancing to two ISPs

Dear Vasillis,

Do you mean It is easier for me to ask both ISP to send the default route?

reg

MHS

Re: LoadBalancing to two ISPs

Hi Alshamlan,

Yes, if you do not need the full routing table to your routes for any special reason, I would recommend to receive just a default route for the reason described to my previous post.

Regards,

Vasilis

New Member

Re: LoadBalancing to two ISPs

Hi Vasillis,

Thanks for your reply. Do you have documents which shows how we can manage the full BGP routing in compare to the managing the default route?

regards

New Member

LoadBalancing to two ISPs

Hi,

If You want more simple construction, You can ask both providers to announce only their own networks, or same far and stable network. Then You can use two static default routes  to these networks.Static routes allow two paralel destinations.

For incoming trafic You can use Your existing solution with /20 to both and /21 or smaller for each.

More complex sollution is to filter routes with route-maps and send community tags to providers, if they accept them.

Re: LoadBalancing to two ISPs

Hi Alshamlan,

No, i do not have any document related to internet routing table management....i have only my experience which I shared with you

Super Bronze

Re: LoadBalancing to two ISPs

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If your platform supports it, see if OER/PfR might work for you.

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