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Can the same AS number be used to run BGP on two seperate networks?

Hi,

We are currently running BGP with one AS Number  on a pair  of Juniper routers at location A. The two routers are  iBGP neighbors directly connecting to each other and they currently advertise the same  ARIN /19 address space out to the internet via ISP A1 and A2.  

We are adding a new datacenter and 3rd Juniper router at remote location Z  and would like to split the existing  /19 space to two separate /20s.  

We would like the traffic for the first /20 to go to the  routers at location A, and traffic for the second /20 to go to  the router at location Z

The router at location Z will not be connected to the routers at location A.  The router at location Z will be connecting to the internet via ISP Z.  The traffic between location A and location Z will routed through the internet

We would like to know if we can use the same ASN to run BGP on both locations. Or do we need another AS to make it work?  Any tips on connecting/routing between the  two locations is greatly appreciated.
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Sparktech8
Asked:
Sparktech8
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1 Solution
 
JFrederick29Commented:
Yes, use the same AS number for both locations.  The AS number is tied to your organization (not the site).
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Sparktech8Author Commented:
Since routers in location A and Z won't be iBGP neighbors, they will have trouble routing to each other using the same ASN and probably reject routes from each other when they see the same ASN from BGP.  I've heard of concept of disconnected ASNs that might work, but not sure how that works.
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JFrederick29Commented:
Sure, if you are going to filter out inbound routes from your ISP's including your AS number.  We have two locations using the same AS number without iBGP between the two locations without any issues.
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Sparktech8Author Commented:
Thx. Are you able to provide some config example or pointers on how to configure this?
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JFrederick29Commented:
Sorry, brain lapse, you are right.  We are only accepting a default route from our ISP's which is why it works :)  A BGP router will discard a prefix with its own AS path in it for loop avoidance.

Are you planning to receive full routes or just a default?

Let me do some digging, standby...
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Sparktech8Author Commented:
We are planning to receive full routes. Thx.
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JFrederick29Commented:
Well in that case, if the two locations need to communicate over the Internet instead of via backend private connections, you'll need a different ASN at the other location so the two sites can communicate.
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Sparktech8Author Commented:
We are using Juniper routers and I think there's a setting that allows you to accept routes that have your own ASN in it. something like a "loops" command
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JFrederick29Commented:
I need more coffee today.

In the Cisco world you can allow prefixes containing your AS in the path using the "allowas-in" neighbor option. Looks like it is the same in JUNOS.

http://www.juniper.net/techpubs/software/erx/junose81/swcmdref-n-z/html/n-commands8.html

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Sparktech8Author Commented:
The Junos syntax for Juniper M-series router is "loops"
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