SMUCSE 8344 MPLS Virtual Private Networks (VPNs)

SMUCSE 8344 When VPN? Internet as your own private network –Communicate securely between various corporate sites (Intranet) –Communicate securely between partner sites (Extranet) –Connect remote dial-up users securely to corporate networks

SMUCSE 8344 Advantages Flexible and cost effective Better business-to-business connectivity –business partners, service providers, contractors, and customers Advances in security

SMUCSE 8344 Layer2 vs. Layer3 VPNs Layer 3 VPNs Layer 2 VPNs Provider devices forward customer packets based on Layer 3 information (e.g., IP) MPLS/BGP VPNs (RFC 2547), GRE, virtual router approaches SP involvement in routing Provider devices forward customer packets based on Layer 2 information “pseudo-wire” concept Tunnels, circuits, LSPs, MAC address

SMUCSE 8344 Layer2 Example IP or MPLS Core IP Core R2R1 L2TPv3 Tunnel Ethernet IPL2TPEthernet Server B Workstation A Step #2 R1 takes Ethernet frame and encapsulates it in L2TP and routes it to tunnel destination Step #3 R2 receives IP/L2TP/Ethernet Packet and removes the IP/L2TPv3 headers. The remaining Ethernet frame is forwarded to Server B. Step #1 Workstation A sends packet destined for Server B

SMUCSE 8344 Overlay Model Each site has a router connected via P-T-P links to routers on other sites –Leased lines –Frame relay –ATM circuit Connectivity –Fully connected –Hub-and-spoke

SMUCSE 8344 Limitations of Overlay Customers need to manage the back-bones Mapping between Layer2 Qos and IP QoS Scaling problems –Cannot support large number of customers –(n-1) peering requirement

SMUCSE 8344 The Peer Model Aims to support large-scale VPN service Key technologies –Constrained distribution of routing info. –Multiple forwarding tables –VPN-IP addresses –MPLS switching

SMUCSE 8344 Terminology CE router Customer Edge router PE router –Provider Edge router. Part of the P-Network and interfaces to CE routers P router –Provider (core) router, without knowledge of VPN

SMUCSE 8344 Terminology (cont’d) Route Distinguisher Attributes of each route used to uniquely identify prefixes among VPNs (64 bits) VPN-IPv4 addresses Address including the 64 bits Route Distinguisher and the 32 bits IP address VRF –VPN Routing and Forwarding Instance –Routing table and FIB table

SMUCSE 8344 Connection Model The VPN backbone is composed by MPLS LSRs PE routers (edge LSRs) P routers (core LSRs) PE routers are faced to CE routers and distribute VPN information through BGP to other PE routers P routers do not run BGP and do not have any VPN knowledge

SMUCSE 8344 Model (cont’d) P and PE routers share a common IGP PE and CE routers exchange routing information through: EBGP, OSPF, RIP, Static routing CE router run standard routing software

SMUCSE 8344 Routing The routes the PE receives from CE routers are installed in the appropriate VRF The routes the PE receives through the backbone IGP are installed in the global routing table By using separate VRFs, addresses need NOT to be unique among VPNs

SMUCSE 8344 Forwarding PE and P routers have BGP next-hop reachability through the backbone IGP Labels are distributed through LDP (hop-by-hop) corresponding to BGP Next-Hops Label Stack is used for packet forwarding Top label indicates Next-Hop (interior label) Second level label indicates outgoing interface or VRF (exterior label)

SMUCSE 8344 Forwarding (cont’d) The upstream LDP peer of the BGP next-hop (PE router) will pop the first level label The egress PE router will forward the packet based on the second level label which gives the outgoing interface (and VPN)

SMUCSE 8344 Forwarding Example PE2 PE1 CE1 CE2 P1 P2 IGP Label(PE2) VPN Label IP packet PE1 receives IP packet Lookup is done on site VRF BGP route with Next-Hop and Label is found BGP next-hop (PE2) is reachable through IGP route with associated label IGP Label(PE2) VPN Label IP packet P routers switch the packets based on the IGP label (label on top of the stack) VPN Label IP packet Penultimate Hop Popping P2 is the penultimate hop for the BGP next- hop P2 remove the top label This has been requested through LDP by PE2 IP packet PE2 receives the packets with the label corresponding to the outgoing interface (VRF) One single lookup Label is popped and packet sent to IP neighbour IP packet CE3

SMUCSE 8344 Scalability Existing BGP techniques can be used to scale the route distribution Each edge router needs only the information for the VPNs it supports Directly connected VPNs Easy to add new sites –configure the site on the PE connected to it, the network automatically does the rest

SMUCSE 8344 QoS Support Pipe model –Similar to int-serv –Unidirectional as opposed to bi-directional model in ATMs Hose Model –Similar to diff-serv