addressing ( public or private ) is used when connecting two AS

[CiscoClub]

I am wondering what type of addressing ( public or private ) is used when connecting two AS:

let us say i have a midsize company, i got a public ASN  and i want to run eBGP between my CE Router and the upstream Service Provider to advertise a network. in this case what type of ip addresses i use on the link(s) that connect me with the ISP(s)

[Georg Pauwen]

Hello,

the short answer is: it is not your choice. You will get the (public) IP addresses from your ISP.

[CiscoClub]

But why they waste two public IPs when the network on the link between the two AS is not advertised ?

[Georg Pauwen]

Hello,

sorry for the confusion: which network do you want to advertise ? You only need a public IP address when you are advertising a public network...

Can you draw up what your setup looks like ?

[CiscoClub]

i mean the ip addresses that set on the interfaces f0/0 in the attached photo, should they be public or private ??

[Georg Pauwen]

Hello,

AS24 and AS40 are public AS numbers, you only need those if you have Internet access. So you need to connect them with public IP addresses on the FastEthernet interfaces.

[paul driver]

Hello

It all depends on if the ASN need to be a registered one - it doesn't have to be?

If you are going to connect to two different ISP's then your site would need to be registered between ASN 1-64511

However is you need to connect to a single ISP ( single or dual homed connection) then the ASN can be a private one - 64512 -65535 - Now any update to the ISP from your site will include its private ASN, thus the isp will remove this from the as-path it advertised to nay of it peers.

res
Paul

[CiscoClub]

Dear Paul;

Kindly note that my question was about the ip addresses ( and not the ASN number) needed to be assigned to the interfaces f0/0 on both side of the link that connect the two autonomous systems, those IPs, do they need to be public or not ?

Thanks in advance.

[paul driver · Accepted solution]

Hello

you will require public address when using two separate isps - as I stated you also need public ASN

the reason being is that they both need to advertise your address space to their own peers  which 9/10 would be a summary of the what they give you 

res

paul