OSPF Sham-Link Support for MPLS VPN

Feature Overview

Figure 1 OSPF Connectivity Between VPN Client Sites and an MPLS VPN Backbone

Area 1

Area 1

MPLS VPN

Area 2

Superbackbone

 

Area 0

Area 0

Area 3

70390

When OSPF is used to connect PE and CE routers, all routing information learned from a VPN site is placed in the VPN routing and forwarding (VRF) instance associated with the incoming interface. The PE routers that attach to the VPN use the Border Gateway Protocol (BGP) to distribute VPN routes to each other. A CE router can then learn the routes to other sites in the VPN by peering with its attached PE router. The MPLS VPN superbackbone provides an additional level of routing hierarchy to interconnect the VPN sites running OSPF.

When OSPF routes are propagated over the MPLS VPN backbone, additional information about the prefix in the form of BGP extended communities (route type, domain ID extended communities) is appended to the BGP update. This community information is used by the receiving PE router to decide the type of link-state advertisement (LSA) to be generated when the BGP route is redistributed to the OSPF PE-CE process. In this way, internal OSPF routes that belong to the same VPN and are advertised over the VPN backbone are seen as interarea routes on the remote sites.

For basic information about how to configure an MPLS VPN, refer to:

http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t5/vpn.htm

Using a Sham-Link to Correct OSPF Backdoor Routing

Although OSPF PE-CE connections assume that the only path between two client sites is across the MPLS VPN backbone, backdoor paths between VPN sites (shown in grey in Figure 2) may exist. If these sites belong to the same OSPF area, the path over a backdoor link will always be selected because OSPF prefers intraarea paths to interarea paths. (PE routers advertise OSPF routes learned over the VPN backbone as interarea paths.) For this reason, OSPF backdoor links between VPN sites must be taken into account so that routing is performed based on policy.

Cisco IOS Release 12.2(8)T

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Cisco Systems 1400 series, 1600R manual Using a Sham-Link to Correct Ospf Backdoor Routing
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1600R, 1600, 1400 series specifications

Cisco Systems 1600 series routers are well-regarded in the networking industry for their reliability, versatility, and performance. Designed to meet the needs of small to medium-sized businesses, the Cisco 1600 series is primarily oriented towards providing robust connectivity for branch offices and remote sites.

One of the most significant features of the Cisco 1600 series is its modular architecture. This allows users to customize their routers with various interface cards, enabling support for different types of WAN technologies, including serial, ISDN, and Frame Relay. The modular design not only enhances flexibility but also extends the lifespan of the equipment, as businesses can upgrade their capacity and functionalities according to evolving demands.

Another key characteristic of the Cisco 1600 routers is their advanced routing capabilities. These devices support a wide range of routing protocols, including RIP, OSPF, EIGRP, and BGP. This versatility ensures seamless integration into existing network infrastructures, facilitating the scalability and adaptability that modern networks require.

Security is also a crucial aspect of the Cisco 1600 series. Incorporating features such as access control lists (ACLs) and support for Virtual Private Networks (VPNs), these routers help businesses safeguard their sensitive data during transmission. Enhanced security features allow companies to implement secure remote access for employees, thereby maintaining productivity without compromising safety.

In addition to routing and security, the Cisco 1600 series boasts Quality of Service (QoS) capabilities. This technology enables better management of network traffic, ensuring that critical applications receive the bandwidth they need for optimal performance. By prioritizing important data flows, businesses can enhance user experience and minimize disruptions across their network.

The Cisco 1600 series routers are also equipped with user-friendly interfaces and management tools. Cisco's IOS software platform provides a command-line interface (CLI) and web-based graphical interface for straightforward configuration and monitoring. This simplifies network management tasks and reduces the learning curve for IT personnel.

In summary, the Cisco Systems 1600 series routers offer a significant combination of modularity, robust routing protocols, enhanced security measures, Quality of Service features, and user-friendly management options. These characteristics make them an excellent choice for small to medium-sized enterprises looking to establish a reliable and secure networking infrastructure. With the continued evolution of networking technologies, the Cisco 1600 series stands as a dependable solution for businesses navigating an increasingly complex digital landscape.
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