MPLS Virtual Private Networks (VPNs) SMU CSE 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 SMU CSE 8344

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

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

Step #1 Workstation A sends packet destined for Server B Layer2 Example 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. IP or MPLS Core IP Core Step #1 Workstation A sends packet destined for Server B R1 R2 IP L2TP Ethernet Ethernet Ethernet L2TPv3 Tunnel Server B Workstation A SMU CSE 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 SMU CSE 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 SMU CSE 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 SMU CSE 8344

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

Terminology (cont’d) Route Distinguisher VPN-IPv4 addresses VRF 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 SMU CSE 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 SMU CSE 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 SMU CSE 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 SMU CSE 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) SMU CSE 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) SMU CSE 8344

Forwarding Example CE1 PE1 CE2 P1 P2 PE2 CE3 SMU CSE 8344 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 IGP Label(PE2) VPN Label IP packet P routers switch the packets based on the IGP label (label on top of the stack) CE1 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 PE1 CE2 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 P1 P2 PE2 CE3 SMU CSE 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 SMU CSE 8344

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