R0106-HP MSR Router Series MPLS Configuration Guide(V7)

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The public tunnel from PE 3 to ASBR 2 is set up. The next hop for the route to PE 1 is ASBR 2. The
incoming label for the public tunnel on ASBR 2 is L3, and the outgoing label is L2.
6. Within AS 200, the public tunnel from PE 3 to ASBR 2 is required to be set up hop by hop through
a label distribution protocol, for example, LDP.
MPLS packets cannot be forwarded directly from PE 3 to ASBR 2. Assume that the outgoing label
for the public tunnel on PE 3 is Lv.
After route advertisement and public tunnel setup, a packet is forwarded from CE 3 to CE 1 by using the
following process:
7. PE 3 performs the following routing table lookups for the packet:
a. Finds a matching route with next hop PE 1 and inner label Lx, and encapsulates the packet with
label Lx.
b. Finds the route to PE 1 with next hop ASBR 2 and label L3, and encapsulates the packet with
label L3 as the outer label.
c. Finds the route to ASBR 2 with outgoing label Lv, and encapsulates the packet with label Lv as
the outmost label.
8. AS 200 transmits the packet to ASBR 2 by the outmost label.
9. ASBR 2 removes the outmost label, replaces L3 with L2, and forwards the packet to ASBR 1.
10. ASBR 1 replaces L2 with L1, and forwards the packet.
11. AS 100 transmits the packet to PE 1 by the outer label.
12. PE 1 removes the outer label, and forwards the packet to CE 1 according to the inner label Lx.
As shown in Figure 49, t
o improve scalability, you can specify an RR in each AS to exchange VPN-IPv4
r
outes with PEs in the same AS. The RR in each AS maintains all VPN-IPv4 routes. The RRs in two ASs
establish a multihop MP-EBGP session to advertise VPN-IPv4 routes.
Figure 49 Network diagram for inter-AS option C using RRs
Carrier's carrier
If a customer of an MPLS L3VPN service provider is also a service provider:
• The MPLS L3VPN service provider is called the provider carrier or the Level 1 carrier.
VPN 1
PE 1
PE 3
VPN 1
CE 3
CE 2
VPN 2 VPN 2
PE 4
CE 4
CE 1
AS 100
PE 2
M
P-I
B
G
P
M
P-
IBGP
ASBR 1
(PE)
RR 1
RR 2
ASBR 2
(PE)
IBGP
IBGP
EBGP
Multi-hop MP-EBGP
VPN LSP
LSP
AS 200
MP-I
B
G
P
MP
-
IBG
P
MPLS backbone
MPLS backbone
Private LSP
Public LSP