© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-1 Connecting an Enterprise Network to an ISP Network Planning the Enterprise-to-ISP Connection

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-2 Enterprise session initiation requirement:  One-way: Connectivity from an enterprise network toward the Internet is the only connectivity required.  Two-way: Connectivity from the Internet to an enterprise network is also required. Solutions:  One-way: private IP address space with address translation  Two-way: public IP address space (in combination with private) and proper routing Session Origin Initiation

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-3  Public IP address space (subpool or whole /24 subnet)  Link type and bandwidth availability  Routing options  Connection redundancy  Independency in regard to an ISP: –Public IP address space –AS number Enterprise Network-to-ISP Connectivity Requirements

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-4 Reachability  Circuit emulation  Static routes  MPLS VPNs  BGP Static routes and BGP are typically selected for Internet connectivity. Previously covered Not covered yet

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-5 Using Circuit Emulation  Used to provide different Layer 2 connectivity to customers via the common Layer 3 infrastructure of a service point –Ethernet, Frame Relay, PPP, HDLC, ATM, Layer 2 connectivity –No routing with the service point from the customer perspective

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-6 Using Static Routes  The customer uses the default route toward the ISP.  The service provider uses static route(s) for customer public networks.  No automatic adjustment to any changes in the network.

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-7 Using MPLS VPN  Used to connect multiple customer locations via a service provider’s common Layer 3 infrastructure –A special VPN can be used to provide Internet connectivity –Routing used can be static or dynamic depending on the SP –The customer routers are connected to the service provider PE routers

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-8 Using BGP  The customer deploys BGP to announce its public networks  The ISP announces a default route, a subset of Internet routes, or a complete Internet routing table  Typically used for inter-AS routing CPE—Customer to Provider Edge router

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-9  Single-homed  Dual-homed  Multihomed  Dual-multihomed Enterprise Network-to-ISP Connection Options

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-10 Link failure results in broken connectivity. Option 1: Routing with static routes  A default route from an enterprise network  A static route(s) from an ISP for customer networks Option 2: Routing with BGP  The customer announces its public network(s)  The ISP announces the default route to the customer Single-homed ISP Connectivity

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-11 Dual-homed ISP Connectivity Characteristics:  Connected with two links to the same ISP  Can use a single router or two edge routers  Can use static routes or BGP

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-12 Characteristics:  Connected to two or more different ISPs  Can use a single router or multiple edge routers  Dynamic routing with BGP Multihomed ISP Connectivity

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-13 Dual-multihomed ISP Connectivity Characteristics:  Connected to two or more different ISPs with two links per ISP  Typically uses multiple edge routers (one per ISP)  Dynamic routing with BGP

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-14 Summary  Connecting an enterprise network to an ISP requires, at a minimum, a public IP address pool, a proper link to the ISP, consideration of redundancy requirements, and the proper routing protocol.  To exchange routing updates with an ISP, the customer can use different options. Static routes and BGP are the options that are most commonly used.  The way in which the customer connects to an ISP depends on the redundancy requirements, where a single-homed connectivity has no redundancy, and the dual-multihomed connectivity has the most redundancy built in.

© 2009 Cisco Systems, Inc. All rights reserved.ROUTE v1.0—6-15