MPLS VPN BGP Role

• BGP well suited to carry the traffic of  hundreds of thousands of routes.
• It is flexible & extended policies to be implemented.
• So it is used well in MPLS VPN.
• In MP BGP 4 address families will be supported.
• IPv4
• IPv6
• VPNv4
• VPNv6
• Remaining are unicast, multicast & VRF
• BGP Extended Community: RT
• It tells to the PE routers if the route imported into a VRF add at least one RT to that IPv4 route

Order

• IP IGP routing protocols build the ip tables.
• LSR assign a local label for each route learned(but not bgp learned routes)
• LSRs share their labels with other LSRs using LDP
• LSRs build their own LIB(Label Information Base), LFIB(Label Forward Information Base) & FIB(Forward Information Base) based on what they have learned from their LDP neighbor.

LDP Neighbor:

• Hellow Messages
• LDP link hello uses destination UDP port 646 & is sent to 224.0.0.2 every 5 sec.
• Session is TCP based on destination port 646.
• Router with highest LDP router ID(Active LSR) will initiate TCP session.
• Keepalives are sent for every 60 sec.
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MPLS VPN Routes Updating

• IGP or eBGP are advertises the CE routes in PE routing table
• At PE router IPv4 routes learned from the CE router is inserted into VRF routing table
• PE routers are fully meshed with MP-BGP.
• To this updated VRF routes RD is added & make them VPNv4 route & then RTs are added.
• Then these VPNv4 routes are redistribute into MP-BGP.
• The iBGP between PEs advertises the VPNv4 route with MPLS label & RTs
•  RTs tells that which vrf can import which route.
• After that RD is removed from VPNv4 route.
•  Then IPv4 route is inserted into VRF routing table.
• PE advertises these routes towards the customer routers.

• The communication between sites is controlled by RTs
• An RT is a BGP extended community that indicates which route should be imported from MP-BGP into the VRF.
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• An RT is a BGP extended community.
• that indicates which routes should be imported from MP-BGP into the VRF.
• Exporting an RT means,
• that the exported vpnv4 route receives an additional BGP extended community, this is the RT, when the route is redistributed from the vrf routing table into MP-bgp.
• Importing an RT means,
• received vpnv4 route from mp-bgp is checked for a matching extended community, this is the rt,.
• If the result is a match, the prefix is put into the vrf routing table.