RE: Route Target in BGP/MPLS IP VPN

[E.T.Metz at telecom.tno.nl]

In a hub-and-spoke VPN, spoke-sites (assuming these do not share a VRF
when connected to the same PE) cannot communicate with eachother
directly, i.e. spoke-PE to spoke-PE. If spoke-sites need to communicate
with eachother the communication path indeed goes (must go) through the
hub-CE, the underlying requirement could e.g. be that traffic between B
and C needs to pass a firewall at A. Note that the hub-PE never acts as
a 'transit' node in this case. To achieve spoke-spoke communication you
either need to advertise an aggregate (covering the spoke-subnets or
entire VPN) or a default from the hub-site (CE), and ensure that the
hub-CE has specific routes to the spoke-CEs pointing to the hub-PE. This
will result in traffic from CE-B to CE-C to go like this CE-B -> PE-B ->
PE-A -> CE-A -> PE-A -> PE-C -> CE-C.

Hope this helps.

cheers,
	Eduard

________________________________

	From: l3vpn-bounces at ietf.org [mailto:l3vpn-bounces at ietf.org] On
Behalf Of Fabien Verhaeghe
	Sent: woensdag 26 januari 2005 14:15
	To: L3vpn at ietf.org
	Subject: Re: Route Target in BGP/MPLS IP VPN
	
	
	Thanks for your answer Taras ,
	 
	What I understood is that Spoke can not communicate DIRECTLY
with each other. They have
	to go through the Hub.
	But if a packet is received at PE C (from the CE) for a
destination address which is in site B he won't
	have any route that says to go through the Hub.
	 
	I'm talking about the routing between PEs when I make a
reference to RFC1771 9.2.1. Not between CE and PE.
	 
	Fabien
	 
	----- Original Message ----- 
	From: TYushkov at microtest.ru 
	To: fabien.verhaeghe at atosorigin.com ; L3vpn at ietf.org 
	Sent: Wednesday, January 26, 2005 1:29 PM
	Subject: RE: Route Target in BGP/MPLS IP VPN

	Hi,

	The main idea of Hub&spoke is the following: spokes may
communicate with hub, but spokes can NOT communicate with each other.

	So, everything seems to be ok. Site A can communicate with site
B & C, and sites B & C can't communicate with each other.

	As I can understand we may use: RIPv2, OSPF and EBGP to make
routing between PE and CE. So RFC1771 9.2.1 it's not our case.

	 

	Cheers.

	Taras

	
________________________________

	From: l3vpn-bounces at ietf.org [mailto:l3vpn-bounces at ietf.org] On
Behalf Of Fabien Verhaeghe
	Sent: Wednesday, January 26, 2005 3:03 PM
	To: L3vpn at ietf.org
	Subject: Route Target in BGP/MPLS IP VPN
	
	
		Hi,
	 
	I've got a question about the use of "Route Target" in BGP/MPLS
IP VPN
	Section 4.3.5 of  draft-ietf-l3vpn-rfc2547bis-03.txt states:
	 
	"Alternatively, suppose one desired, for whatever reason, to
create a
	"hub and spoke" kind of VPN. This could be done by the use of
two
	Route Target values, one meaning "Hub" and one meaning "Spoke".
At
		the VRFs attached to the hub sites, "Hub" is the Export
Target and
	"Spoke" is the Import Target. At the VRFs attached to the spoke
		site, "Hub" is the Import Target and "Spoke" is the
Export Target."
	 
	If I have 3 sites A,B,C. one CE/PE pair for each site and one
VRF per CE/PE.
	Site A is the hub
	Site B,C are spoke
	 
	In A VRF I would have the routes to both sites B and C
	In B,C VRF I would only have routes to A since with BGP routes
learned from IBGP are not
	advertised to BGP peer in the same AS (RFC 1771 9.2.1).
	 
	So how can systems in site B communicate with systems in site C?
	 
	I guess I misunderstood something, and PE connected to site A
will actually advertised routes received from site C
	to site B. But it seems inconsistent with RFC 1771 9.2.1.
	 
	Can someone explain to me please?
	 
	Thanks
	Fabien