17-48 Riverstone Networks RS Switch Router User Guide Release 8.0
Configuring L3 Label Switched Paths MPLS Configuration
BGP Traffic over an LSP Configuration Example
In traditional BGP networks, BGP must be run on every router in order to provide packet forwarding. If BGP routing
information is not propagated to all routers, including backbone routers, packets may not be able to be routed to their
BGP destinations. You can run MPLS in a BGP network to remove BGP routing from backbone routers. Removing
BGP from the backbone network provides the following benefits:
•Memory requirements for backbone routers is reduced, as they do not have to store extensive routing
information
•Backbone routers do not have to perform BGP update processing, thus saving CPU utilization
•Routing tables are more stable, because backbone routers do not have to process route flaps
In Figure17-11, R7 in AS 63498 and R9 in AS 65498 are running BGP. BGP traffic between R7 and R9 is routed
through AS 64498 where OSPF is running as the IGP. Routers R3 and R6 are LSRs running MPLS and LDP, in
addition to BGP.
R3 and R6 are ingress and egress LSRs for bidirectional LSPs. R1 is a transit LSR. On the LSPs, the BGP traffic is
label switched, with LDP as the label signaling protocol. (RSVP can be used in MPLS networks where traffic
engineering is needed.) R3 and R6 use labels that are generated for the next-hop addresses of advertised BGP routes.
Packets with BGP destinations are sent across the LSPs with labels that correspond to the egress LSR that advertised
the external route. Note that R1 and any other transit LSRs on the LSPs do not need to perform IP lookups nor do they
need to learn BGP routing information to forward packets.
Figure 17-11BGP traffic over a n MPLS LSP
Timesaver Click on the router name (in blue) to see the corresponding configuration.
R9
R6
AS 64498 AS 65498
AS 63498
R7 R3 R1
EBGP Route
LSP