1. MBGP and Customer Routes
Advanced Communications 2007 Week 11 Lecture 1
by Donald Neal

2. To Make This Happen We Need
IP routing for internal use
PE's holding large numbers of distinct routing tables – VPN Routing and Forwarding Instances
A way of passing label information around
LDP – Label Distribution Protocol
RSVP – Resource Reservation Protocol
Or both
A way of passing customer routes tied to labels
MBGP – Multiprotocol BGP

3. BGP

4. Route Distinguishers “4.1. The VPN-IPv4 Address Family
The BGP Multiprotocol Extensions [BGP-MP] allow BGP to carry routes
from multiple "address families". We introduce the notion of the
"VPN-IPv4 address family". A VPN-IPv4 address is a 12-byte quantity,
beginning with an 8-byte Route Distinguisher (RD) and ending with a
4-byte IPv4 address. If several VPNs use the same IPv4 address
prefix, the PEs translate these into unique VPN-IPv4 address
prefixes. This ensures that if the same address is used in several
different VPNs, it is possible for BGP to carry several completely
different routes to that address, one for each VPN.”
- RFC4364

5. Route Distinguisher (64 bits)
VPN-IPv4 Encoding
Route Distinguisher (64 bits)
IPv4 Address(32 bits)
Type 0
AS Number
Assigned Number
Type 1
IP Address
Assigned Number
Type 1
Type 2
AS Number
IP Address
Assigned Number
Assigned Number
e.g. 681:514:

6. Route Targets “4.3.1. The Route Target Attribute
Every VRF is associated with one or more Route Target (RT)
attributes.
When a VPN-IPv4 route is created (from an IPv4 route that the PE has
learned from a CE) by a PE router, it is associated with one or more
Route Target attributes. These are carried in BGP as attributes of
the route.
Any route associated with Route Target T must be distributed to every
PE router that has a VRF associated with Route Target T. When such a
route is received by a PE router, it is eligible to be installed in
those of the PE's VRFs that are associated with Route Target T.”
“There is a set of Route Targets that a PE router attaches to a route
received from site S; these may be called the "Export Targets". And
there is a set of Route Targets that a PE router uses to determine
whether a route received from another PE router could be placed in
the VRF associated with site S; these may be called the "Import
Targets". The two sets are distinct, and need not be the same.”
“The Route Targets discussed herein are encoded as BGP
Extended Community Route Targets [BGP-EXTCOMM]. They are structured
similarly to the RDs.”
“Note that a route can only have one RD, but it can have multiple
Route Targets.”
-RFC4364

7. VRF's One VRF per address space (e.g. per customer) One RD to one VRF
Must have a route import policy
Must have a route export policy
Interfaces to customer routers assigned to a VRF
Each PE needs peer with each other PE only once for all VRF's

8. VRF's ip vrf voice rd 65300:101 route-target import 65300:101
route-target export 65300:101
- Broadband Network Architectures p.72

9. PE Peering AKL-PE2 TAU-PE1 AKL-PE1 AKL-P1 MAN-P1 TAU-P1 HAM-PE2 HAM-P1.
TAU-PE1
AKL-PE1
AKL-P1
MAN-P1
TAU-P1
HAM-PE2
HAM-P1
HAM-PE1
ROT-P1

10. Multiprotocol Reachable NLRI
AFI 1 = IPv4
SAFI 1 = Unicast
SAFI 128 = Labelled VPN Unicast
NLRI
When a PE router distributes a VPN-IPv4 route via BGP, it uses its
own address as the "BGP next hop". This address is encoded as a
VPN-IPv4 address with an RD of 0. ([BGP-MP] requires that the next
hop address be in the same address family as the Network Layer
Reachability Information (NLRI).) It also assigns and distributes an
MPLS label. (Essentially, PE routers distribute not VPN-IPv4 routes,
but Labeled VPN-IPv4 routes. Cf. [MPLS-BGP].)
- RFC4364 (Reference is to RFC3107)

11. The Way of the MPLS VPN Packet(1)CE
IP Packet forwarded from customer router to PE router HAM-PE1
HAM-PE1 pushes (prepends) two labels to packet
Labelled packet forwarded
TAU-PE1
AKL-P1
TAU-P1
To TAU-PE1
To Customer on TAU-PE1
100301
101539
IP Packet
HAM-P1
ROT-P1 CE
HAM-PE1

12. Which VRF's? AKL-PE2 TAU-PE1 AKL-PE1 AKL-P1 MAN-P1 TAU-P1 HAM-PE2.
TAU-PE1
AKL-PE1
AKL-P1
MAN-P1
TAU-P1
HAM-PE2
HAM-P1
HAM-PE1
ROT-P1

13. In My VRF Definition Route Distinguisher Import Route Target
Export Route Target
Interface (to CE)
RIP routing instance (to CE)

14. In My VRF Definition Route Distinguisher Import Route Target
Another Import Route Target
Export Route Target
Interface (to CE)
RIP routing instance (to CE)

15. Route Targets ”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.”
-RFC4364

16. Internet Access (1) Internet CE TAU-PE1 AKL-P1 TAU-P1 HAM-P1 ROT-P1 CE
HAM-PE1

17. Internet Access (2) Internet CE TAU-PE1 AKL-P1 TAU-P1 HAM-PE2 HAM-P1
ROT-P1 CE
HAM-PE1

18. Internet Access (2) Internet CE AKL-PE2 TAU-PE1 AKL-P1 TAU-P1 HAM-PE2
ROT-P1 CE
HAM-PE1
Customer VRF

19. Further Reading Broadband Network Architectures pp.67-79
RFC4364 – BGP/MPLS IP VPNs
Broadband Network Architectures pp.67-79

20. Reading for Next Lecture
Kompella & Rekhter, RFC4761 -Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling