1 © 1999, Cisco Systems, Inc _05F9_c2 1 NW’99 Vienna © 1999, Cisco Systems, Inc. MPLS VPNs Peter Tomsu Senior Consultant EMEA Peter Tomsu Senior Consultant EMEA

2 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns 2 © 2000, Cisco Systems, Inc. Agenda VPN Concepts MPLS VPN Connectivity Model Route Distribution Mechanisms Table Population and Packet Forwarding Advanced MPLS VPN Topologies MPLS VPN Convergence

3 © 1999, Cisco Systems, Inc _05F9_c2 3 NW’99 Vienna © 1999, Cisco Systems, Inc. 3 © 2000, Cisco Systems, Inc. VPN Concepts

4 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns Virtual Private Networks Virtual Networks Virtual Private NetworksVirtual Dialup NetworksVirtual LANs Overlay VPNPeer-to-Peer VPN Layer-2 VPNLayer-3 VPN X.25F/R ATM GRE IPSec Access lists (Shared router) Split routing (Dedicated router) MPLS/VPN IP network infrastructure delivering private network services over a public infrastructure - certainly not a new concept Leased lines --> statistical multiplexing schema Delivered at layer-2 (SP backbone) or layer-3 (IP backbone) Private connectivity between multiple sites Global as well as non-unique private IP addressing space between VPNs

5 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns VPN - Overlay Model Service Provider Network Provider Edge (PE) device VPN Site Virtual Circuit CPE (CE) Device Layer-3 Routing Adjacency Private trunks across a Telco/SP shared infrastructure Leased lines, dialup lines FR/ATM virtual circuits IP(GRE) tunnelling Point-to-point solution between customer sites how to size inter-site circuit capacities ? full mesh requirement for optimal routing CPE routing adjacencies between sites

6 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns Service Provider Network Provider Edge (PE) Router VPN Site CPE (CE) Router Layer-3 Routing Adjacency VPN - Peer-to-Peer Model Provider Edge (PE) device exchanges routing information with CPE all customer routes carried within SP IGP simple routing scheme for VPN customer routing between sites is optimal circuit sizing no longer an issue Private addressing is not an option Addition of new site is simpler no overlay mesh to contend with

7 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns Shared or dedicated router approach shared may require complex filtering dedicated is expensive to deploy Cannot deploy duplicate private addressing between customers PE router will hold routes for ALL VPN customers VPN - Peer-to-Peer Model Issues Service Provider Network Provider Edge (PE) Router VPN Site CPE (CE) Router Layer-3 Routing Adjacency

8 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns Solution - MPLS/VPN Model Combine benefits of overlay and peer-to-peer models overlay (security and isolation between customers) peer-to-peer (simplified customer routing) PE routers only hold routes for attached VPNs reduces size of PE routing information proportional to number of VPNs attached MPLS used to forward packets (no mor via routing) full routing within backbone no longer required means no more external routing info needed in backbone P-Network PE Router C-Network CE Router VPN Site P Router VPN Site

9 © 1999, Cisco Systems, Inc _05F9_c2 9 NW’99 Vienna © 1999, Cisco Systems, Inc. 9 © 2000, Cisco Systems, Inc. MPLS VPN Connectivity Model

10 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns MPLS/VPN Connectivity Model A VPN is a collection of sites sharing common routing information same set of routes within the routing table A site may belong to more than one VPN through sharing of routing information A VPN can be seen as Closed User Group (CUG) or Community of Interest P-Network PE Router C-Network CE Router VPN Site P Router VPN Site

11 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns VPN Routing & Forwarding Instance – VRF & Global Routing Table PE CE VPN-A CEVPN-B VRF for VPN-A VRF for VPN-B VPN Routing Table CE Global Routing Table IGP &/or BGP Paris London Munich Global routing table contains all PE and P routes populated by the VPN backbone IGP VRF (VPN Routing & Forwarding Instance) associated with one or more directly connected sites (CE routers) associated with any type of interface, whether logical or physical (e.g. sub/virtual/tunnel) interfaces may share same VRF if connected sites share same routing information

12 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns VPN Routing & Forwarding Instance (VRF) VRF can be seen as Virtual Router with the following structures forwarding table based on CEF set of interfaces using the derived forwarding table rules to control import/export of routes from/into the VPN routing table set of routing protocols/peers which inject information into the VPN routing table (including static routing) router variables associated with the routing protocol used to populate the VPN routing table

13 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns MPLS/VPN Connectivity Model Private addressing in multiple VPNs no longer an issue members of a VPN must not use same address range VPN A VPN BVPN C London Milan ParisMunich BrusselsVienna Address space for VPN A and B must be unique / / / / / /24

14 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns VRF Route Population VRF populated locally through PE and CE routing protocol exchange RIP Version 2, OSPF, BGP-4 & Static routing Separate routing context for each VRF routing protocol context (BGP-4 & RIP V2) separate process (OSPF) PE CE Site-2Site-1 EBGP,OSPF, RIPv2,Static

15 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns StaticBGPRIP PE to CE Routing processes Routing contexts VRF Routing tables VRF Forwarding tables Routing processes run within specific routing contexts Populate specific VPN routing table and FIBs (VRF) Interfaces are assigned to VRFs VRF & Multiple Routing Instances

16 © 1999, Cisco Systems, Inc _05F9_c2 16 NW’99 Vienna © 1999, Cisco Systems, Inc. 16 © 2000, Cisco Systems, Inc. MPLS VPN Route Distribution Mechanisms

17 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns VRF Population with MP-iBGP PE CE VPN-A CE VPN-B VRF VPN-AVRF VPN-B CE MP-iBGP PE BGP Tabe Routes from VPN-A Routes from VPN-B Paris London Munich Global Routing Table populated by IGP protocols (e.g. OSPF, IS-IS) may also contain BGP-4 (IPv4) routes does not contain VPN routes VRF routing tables contain VPN specific routes MP-iBGP routes imported into VRFs CE routes populate VRFs based on routing protocol context Global Routing Table IGP &/or BGP

18 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns VRF Route Distribution PE routers distribute local VPN information across MPLS/VPN backbone using MP-iBGP & redistribution from VRFs receiving PE imports routes into attached VRFs PE CE Router P Router Site MP-iBGP

19 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns Receiving PE Router Info Extended Community Attribute BGP transitive optional attribute which contains a set of extended communities SOO - Site of Origin identifies the site that originated a particular route RT - Route Target identifies set of sites to which a particular route should be exported to Route Distinguisher Uniqueness of IPv4 prefix achieved through the use of a RD - 64 bit identifier creates a VPN-V4 Prefix RD + IPv4 Prefix

20 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns PE-1 VRF Population with MP-iBGP PE-1 CE-1 PE-2 BGP, OSPF, RIPv2 update for /24,NH=CE-1 VPN-v4 update RD:1:27: /24 Next-hop=PE-1 SOO=Paris, RT=VPN-A Label=(28) CE-2 Originating PE router translates CE routing update into VPN-V4 route Assign a RD, SOO and RT based on configuration Re-write Next-Hop attribute (to PE loopback) Assign a label based on VRF and/or interface Send MP-iBGP update to all PE neighbors ParisLondon

21 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns MP-iBGP Update PE-1 CE-1 MP-iBGP PE-2 BGP, OSPF, RIPv2 update for /24,NH=CE-1 CE-2 ParisLondon Any other standard BGP attributes Local Preference, MED, Next-hop, AS_PATH, Standard Community Label identifying Outgoing interface or VRF where a lookup has to be performed (aggregate/connected) The BGP label will be the second label in the label stack of packets travelling in the core VPN-v4 update RD:1:27: /24 Next-hop=PE-1 SOO=Paris, RT=VPN-A Label=(28)

22 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns VRF Population of MP-iBGP Update PE1 CE-1 MP-iBGP PE2 ip vrf VPN-B route-target import VPN-A CE-2 Receiving PE routers translate to IPv4 Insert the route into the VRF identified by the RT attribute (based on PE configuration) The label associated to the VPN-V4 address will be set on packets forwarded towards the destination in CE1 VPN-v4 update is translated into IPv4 address put into VRF VPN-A as RT=VPN-A optionally advertised to CE-2 ParisLondon VPN-v4 update RD:1:27: /24 Next-hop=PE-1 SOO=Paris, RT=VPN-A Label=(28)

23 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns P Router MPLS/VPN Backbone VPN A SITE-2 Site-1 routes Site-2 routes Site-3 routes Site-4 routes MP-iBGP Basic Intranet Model Site-3 & Site-4 routes RT=VPN-A Site-1 & Site-2 routes RT=VPN-A Site-1 routes Site-2 routes Site-3 routes Site-4 routes SITE-1SITE-3 SITE-4

24 © 1999, Cisco Systems, Inc _05F9_c2 24 NW’99 Vienna © 1999, Cisco Systems, Inc. 24 © 2000, Cisco Systems, Inc. MPLS VPN Table Population & Packet Forwarding

25 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns P router In Label FEC Out Label /32 - In Label FEC Out Label /32 POP In Label FEC Out Label /32 - MPLS/VPN Table Population Paris Use label implicit-null for destination /32 Use label 41 for destination /32 PE-1 London PE and P routers have BGP next-hop reachability through the backbone IGP Labels are distributed through LDP corresponding to BGP Next-Hops or RSVP with Traffic Engineering /24 VPN-v4 update RD:1:27: /24 Next-hop=PE-1 SOO=Paris, RT=VPN-A Label=(28)

26 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns MPLS/VPN Packet Forwarding Label Stack is used for packet forwarding Top label indicates BGP Next-Hop (interior label) Second level label indicates outgoing interface or VRF (exterior VPN label) MPLS nodes forward packets based on top label any subsequent labels are ignored Ingress PE receives normal IP packets PE router performs IP Longest Match from VPN FIB, finds iBGP next-hop and imposes a stack of labels In Label FEC Out Label /32 41 Paris PE-1 London / VPN-A VRF /24, NH= Label=(28)

27 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns In Label FEC Out Label /32 POP MPLS/VPN Packet Forwarding Paris PE-1 London / VPN-A VRF /24, NH= Label=(28) In Label FEC Out Label 28(V) /24 - VPN-A VRF /24, NH=Paris Penultimate PE router removes the IGP label Penultimate Hop Popping procedures (implicit-null label) Egress PE router uses the VPN label to select which VPN/CE to forward the packet to VPN label is removed and the packet is routed toward the VPN site

28 © 1999, Cisco Systems, Inc _05F9_c2 28 NW’99 Vienna © 1999, Cisco Systems, Inc. 28 © 2000, Cisco Systems, Inc. Advanced MPLS VPN Topologies

29 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns MPLS/VPN Extranet Support PE VPN-A CE VPN-B VRF for VPN-A VRF for VPN-B VPN-A Paris Routes VPN-B Munich Routes CE Extranet VPN Routing Table Paris Munich Extranet support is simply the import of routes from one VRF into another VRF which services a different VPN Controlled through the use of route target if we import the route, we have access Various topologies are viable using this technique

30 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns Central Services Model VPN A Central Server Site VPN B / / /24 VPN A VRF / /24 VPN B VRF / /24 VPN A VRF (Export RT=client-rt) (Import RT=server-rt) VPN B VRF (Export RT=client-rt) (Import RT=server-rt) Server VRF (Export RT=server-rt) (Import RT=server-rt) (Import RT=client-rt) MP-iBGP Update RD: /24, RT=client-rt MP-iBGP Update RD: /24, RT=server-rt MP-iBGP Update RD: /24, RT=client-rt Client sites access central services, no direct communication with other client sites Controlled through the use of Route Target client sites belong to unique VRF, servers share common VRF client exports routes using client-rt and imports server-rt server exports routes using server-rt and imports server-rt & client-rt

31 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns MPLS/VPN Internet Connectivity Static Default Route VPN A /24 Global Internet Access VPN B VPN A VRF NH=Internet-PE VPN B VRF NH=Internet PE Internet Routing Table MPLS/VPN Backbone ip route vrf VPN_A Internet-PE global ip route serial 1/0 ip route vrf VPN_B Internet-PE global ip route serial 1/ /24 Default route provided through static route within the VRF extension to ‘ip route’ command - Global keyword Internet gateway points to an exit point whose address is within the global routing table PE router generates VPN customer routes into BGP through global static routes

32 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns MPLS/VPN Internet Connectivity Dynamic Default Route MPLS/VPN Backbone VPN A VPN A Central Site VPN B Central Site VPN-IPv4 Update Net= /0 RT=17:22 VPN-IPv4 Update Net= /0 RT=17:28 VPN-IPv4 Update Net= /0 RT=17:22 Export VPN A default with RT=17:22 and VPN B default with RT=17:28 VPN A VRF (Import RT=17:22) VPN B VRF (Import RT=17:28) VPN B Default route provided through dynamic default route within the VRF

33 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns Achieved by using a second interface to the client site either physical, or logical such as sub-interface or tunnel Many clients will wish to send/receive routes directly with the Internet default route is not sufficient in this environment Routes reside on the PE router but within the global not VRF tables Mechanism needed to distribute this routing information to VPN customer sites and also receive routes and place them into the global, and not VRF table MPLS/VPN Internet Connectivity Separate BGP Session PE/CE Link PE VPN Site Global Internet Internet Routes (sub)interface associated with global routing table (sub)interface associated with VRF CE

34 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns ISP B ISP A Export default route with Internet_access route target Full Internet Routes PE Static default pointing to loopback interface so lookup in VRF will occur on incoming packets MPLS/VPN Internet Connectivity Global Internet Table Association If multiple exit points then possibility to associate full Internet routes with a VRF if only one exit point then default pointing to internet exit point interface will normally be sufficient With multiple interfaces, sub-optimal routing is a possibility with default route generation as multiple defaults would allow load balancing but no best path selection Association of Internet routes with VRF provide ability to generate aggregate default

35 © 1999, Cisco Systems, Inc _05F9_c2 35 NW’99 Vienna © 1999, Cisco Systems, Inc. 35 © 2000, Cisco Systems, Inc. MPLS VPN Convergence

36 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns End-to-end Routing Convergence PE VPN Client A New VPN route advertised Advertisement of new VPN route to relevant VPN sites New VPN route imported into relevant VRFs New VPN route propagated across MP-iBGP session If link fails, MPLS/VPN backbone IGP converges on new path to BGP next-hop Convergence needs to be assessed in two main areas convergence within the MPLS/VPN backbone convergence between VPN client sites Both areas are completely independent.. but work together to provide end-to-end convergence as perceived by the VPN client therefore must be assessed in conjunction

37 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns PE-1 P-1 VPN Client A Convergence Router Based Backbone MPLS & IGP backbone convergence are closely entwined If P-1 to PE-2 link fails, PE-1 next-hop to destinations reachable via /32 (PE-2 Loopback) will change to P-3. As label exists (41), convergence is as quick as the IGP PE-2 Use label 41 for destination /32 Use label POP for destination /32 Use label 23 for destination /32 Use label 25 for destination /32 P-2 P-3 Use label POP for destination /32

38 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns PE-1 P-1 VPN Client A Convergence ATM Based Backbone MPLS LSR must re-converge on IGP change AND re-signal for label mapping to downstream next-hop If P-1 to PE-2 link fails, PE-1 next-hop to destinations reachable via /32 (PE-2 Loopback) will change to P-3. As label does not exist, PE-1 must signal the next-hop downstream ATM-LSR PE-2 Label request for destination /32 Use label 1/239 for destination /32 P-2 P-3 Use label 1/321 for destination /32 Label request for destination /32

39 Mpls_vpns_09_01 © 2001, Peter Tomsu Mpls_vpns