Juniper JUNOSE 11.2.X BGP AND MPLS, Configuration Manual

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MPLS tunnels are unidirectional; Figure 77 on page 401 shows only the tunnels established
to carry traffic from ASBR 2 to PE 1 and from PE 4 to ASBR 3. Note that ASBR 2 and ASBR
3 are both also PE routers. In that sense, ASBR 2 treats ASBR 3 as a CE router, and ASBR
3 treats ASBR 2 as a CE router.
Inter-AS Option B
The second method is known as inter-AS option B or 2547bis option B, after IETF RFC
4364—BGP/MPLS IP Virtual Private Networks (VPNs) (February 2006). This method
uses BGP to signal VPN labels between the AS boundary routers (Figure 78 on page 402).
The base MPLS tunnels are local to each AS. Stacked tunnels run from end to end
between PE routers on the different ASs. This method provides greater scalability, because
only the BGP RIBs store all the inter-AS VPN routes.
Figure 78: Inter-AS Topology with End-to-End Stacked MPLS Tunnels
PE 1 assigns labels for routes to the customer sites, and distributes both the label
assignments and the VPN-IPv4 routes throughout AS 42 in extended BGP update
messages by means of internal MP-BGP. ASBR 2 then distributes the routes to ASBR 3
with external MP-BGP; ASBR 2 specifies itself as the next-hop address and assigns a
new label to the route so that ASBR 3 can properly direct traffic. ASBR 3 propagates the
routes by internal MP-BGP throughout AS 35, including to PE 4.
Example You can use the show ip bgp vpn all field in-label and show ip bgp vpn all field out-label
commands in the context of each VPN element to display the in label and out label
associated with the route at that point. Suppose that CE 1 advertises a route to prefix
10.10.10.11/32 to its external BGP peer PE 1 (10.2.2.2) in VRF A. PE 1 associates the label
16 with this route; an extended update message sent to internal MP-BGP peer ASBR 2
carries this information as a labeled VPN-IPv4 prefix (label 16, RD 100:0, IPv4 prefix
10.10.10.11/32).
host1:pe1# show ip bgp vpn all field in-label
Prefix In-label
10.10.10.11/32 16
On PE 1, no out label is associated with the IPv4 prefix 10.10.10.11/32.
Copyright © 2010, Juniper Networks, Inc. 402
JunosE 11.2.x BGP and MPLS Configuration Guide