Building a BGP Architecture

Hello all,

I’m new on this forum. Sorry for my bad english, I’m French :smile: I don’t know if I should post my question in this section, but I’m building a BGP Architecture for my company.
This is what my boss want :
We have a /22 subnet of public IP Addresses and we want to announce this subnet on the Internet. In order to doing that we have requested our own ASN to RIPE.
But, and this is where it becomes complex, we have threee different providers. We are going to create a peering with these 3 providers and my boss want to announce a /24 of our /22 to one provider in primary with the two others as secondary. An other /24 to the second provider with two others as secondary, and an other /24 to the third provider with two others as secondary.

So for one /24, flows should come through the first provider, for an other /24, through the second and for an other /24 through the third provider.

I don’t know if it’s possible, but if it is, how can I doing this ?

Thank you

Bonjour Guillaume,

One way of achieving this is by using AS path prepending

For example, let’s say you use address space 192.168.0.0/22 and you use 3 subnets:

* 192.168.0.0/24
* 192.168.1.0/24
* 192.168.2.0/24

You have one router (R1) in AS 1 that is connected to three different providers, ISP1, ISP2 and ISP3 in different ASes.

* Traffic for 192.168.0.0/24 should come in through ISP1.
* Traffic for 192.168.1.0/24 should come in through ISP2.
* Traffic for 192.168.2.0/24 should come in through ISP3.

**To ISP1 you advertise all three subnets but you use AS path prepending like this:**

* 192.168.0.0/24 without AS path prepending
* 192.168.1.0/24 with AS path prepending
* 192.168.2.0/24 with AS path prepending

**To ISP2:**

* 192.168.0.0/24 with AS path prepending
* 192.168.1.0/24 without AS path prepending
* 192.168.2.0/24 with AS path prepending

**To ISP3:**

* 192.168.0.0/24 with AS path prepending
* 192.168.1.0/24 with AS path prepending
* 192.168.2.0/24 without AS path prepending

If you do it like this, there will be a preferred path for each of your subnets. Does this make sense?

Rene

Hello Rene,

Thank you for your quick answer. I’m going to try it next my in my lab.

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