Inter AS VPN question

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Jul 17th, 2006
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a global question is when using Inter AS VPN , and i am using Private AS , and will be connecting to another provider with Public AS.

do i need to register a public AS alos for this scenario , or i can run the service with my own private AS without having to change it.

taking into consideration that will most probably use VRF-VRF connection as based on RFC 4364


Correct Answer by Harold Ritter about 11 years 1 month ago

The AS path on prefixes received from the other AS via BGP on the VRF interface will definitely be propagated via VPNv4 as well as all the other transitive attributes.


Hope this helps,

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Harold Ritter Mon, 07/17/2006 - 04:08
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You can indeed use the private AS number as long as the other SP has no problem with it.


Hope this helps,

olorunloba Mon, 07/17/2006 - 09:52
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Using the back to back VRF solution, I doubt the other SP would mind. This is because your routes will appear in a vrf on the other SPs router. I doubt the SP will complain about having private addresses in a VRF.


Harold Ritter Mon, 07/17/2006 - 12:09
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Olorunloba,


I was referring to the private ASN, not the private addresses. In the case of private ASNs, the other SP might have already allocated the private ASN to another of its MPLS VPN customers. Beyond that, it shouldn't be an issue.


Regards,

mohamedhaddad Mon, 07/17/2006 - 20:39
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what if the other SP had already allocated the private ASN to another MPLS VPN customer , i guess as per your reply , this also won't affect the case, because this ASN will not be shown in the global routing table , so it won't affect anything. !!

am i right??

mohamedhaddad Mon, 07/17/2006 - 20:52
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one thing also appeared in my mind ..

aren't we going to redistribute the routes receieved from BGP into the MP-BGP .will this also transfere the ASN with the route distributed..? if yes , will this also affect the Private ASN assigned , will it make a conflict ?or it will be also within that VPN so will not make any conflict.


Regards

Harold Ritter Tue, 07/18/2006 - 03:48
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Correct. The prefixes learnt via the bgp session between the two SP networks will be propagated into the SP VPNv4 session along with the private AS. It would only conflict if you were to propagate these updates to a customer using the same ASN to connect to the MPLS VPN network. There is ways such as remove-private-as, as-override or allowas-in to solve this though.


Hope this helps,

mohamedhaddad Tue, 07/18/2006 - 04:21
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Thanks for the reply , but why would the ASN be transfered with the VPN-V4 address from the SP1-PE facing the SP2-PE to the remote PE of SP1 ..

i am not sure, but i guess the MP-BGP will transfere only the IP prefexes, VPN-V4 addresses, not any other BGP attribute that were learned with the route in the SP1-PE to SP2-PE BGP session.



Correct Answer
Harold Ritter Tue, 07/18/2006 - 05:23
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The AS path on prefixes received from the other AS via BGP on the VRF interface will definitely be propagated via VPNv4 as well as all the other transitive attributes.


Hope this helps,

olorunloba Tue, 07/18/2006 - 06:34
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Thanks Harold, I was thinking the conversation was about IP addresses.


mohamedhaddad,

Other BGP attributes are also advertised under the eBGP session, in accordance with normal BGP rules. For example, your route-targets communities are also advertised.


Note that if you are using the back-to-back vrf solution, you do not have to use BGP to peer the AS together, and then the BGP attributes will be lost, if this is what you want.



Harold Ritter Tue, 07/18/2006 - 03:42
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Correct. It shouldn't an issue technically speaking but certain SP might have issues with using the same private ASN for different customers. I guess it boils down to discussing it with the other SP.


Thanks for your reply,

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