as-number on 5 locations

[husamaga1]

Hello,

I have a question for my situation here.

i have a big network with far locations. so i need to make 5 bgp sessions with the same ISP from 5 locations.

my question is that possible?

i have a set of IP's : 176.xxx.160.0/19

and ASN: 31789

i want to use the set like this:

Location 1: 176.xxx.160.0/22

Location 2: 176.xxx.164.0/22

Location 3: 176.xxx.168.0/22

Location 4: 176.xxx.172.0/22

Location 5: 176.xxx.176.0/22

Can i make BGP with the same ISP from 5 difirent locations? and advertise the needed ip's?

Can i do that without making an eBGP between my routers?

Best regards.

[smitesh kharecha · Accepted solution]

Hi,

You can use the same AS number at any number of different locations.

However, they won't be able to communicate within themseleves as by default as per BGP rules, BGP will reject any prefix which will have its own AS number.

So, to make the concept work, you have to make IBGP between all the sites and make one of them as route-reflector.

Regards,

Smitesh

PS: Please rate helpful posts.

[husamaga1]

Thanks for your reply.

So you are saying that i have to make an IBGP between all locations? that meens 15 ibgp sessions between routers.?

also, when i make IBGP between all these locations, what should i use?

let say on location one is my cisco core switch with as-number. and i have to advertise the prefix /22 on it, and then use the same as-number on the second router on location 2 with prefix of /22 and the same as-number? and when make all ibgp sessions between the routers&switches i can make the bgp session to my ISP? as a regular bgp session to the ISP on every location but with other perfixes advertised?

how can i make the route-reflector & what does reflector doe's ?

Regards

[smitesh kharecha · Accepted solution]

Hi,

Please see attached topology.

You will be given /30 IP address by your ISP at every location.

You will run eBGP with your ISP at evey location.

Now, since you are already given /30 IP address by your ISP, you can have iBGP on  those IP address.

In the sample topology, I have made Site A as route reflector and rest site will have iBGP peering with Site A only.

PS: Sorry for hasty and untidy visio.

Regards,

Smitesh

[husamaga1]

Thanks. this helped.

so , in every location i will advertised only my set of /22 , except on the reflector i can use the /19? or i must do the same at all locations? do i make ibgp with the same as-number also?

sorry for these all questions but really i need to understand that.

Regards

[smitesh kharecha · Accepted solution]

Hi,

At all of your site you will advertise /22 only, including your route-reflector site.

iBGP means BGP peering with same AS. Hence at all of your sites AS number will be same.

At all sites ( apart from route-reflector) you will be having two bgp peers, one eBGP with ISP and other iBGP with route-reflector.

At route-reflector site, you will be having one eBGP with ISP and 4 iBGP with rest of your sites.

Regards,

Smitesh

[husamaga1]

Okay, thanks for your answer. i understood that

Best regards.

[husamaga1]

Okey,

here what i done:

i used the /30 ip's from my ISP for iBGP, and i make the connections and it's established with multihop. i didn't advertised any thing yet. should i advertised my /22 set on iBGP? & also advertised the same thing on the eBGP?

Regards

[smitesh kharecha]

Hi,

Yes, you need to advertise /22 at every location in eBGP and iBGP.

Regards,

Smitesh

[Alessio Andreoli]

Hi there,
You can do it indeed. Just remember to implement the local-as command or ask to your service provider if it is possible to override your as number with theirs. Generally the second solution is a better design.

Alessio

Sent from Cisco Technical Support iPad App

[husamaga1]

Thanks for your answers,

i'm sorry i'm late with my report.

i make bgp with my ISP, and advertised set of ipv4 addresses, i used ip xxx.xxx.xxx.1 from my set to create bgp connections. so every thing works fine.

P.S. i didn't use reflector.