Because they can build the OSPF adjacency directly with each other, the routes exchanged between the PE's will remain intra area routes. When a sham-link is configured between PE routers, the PEs can populate the VRF routing table with the OSPF routes learned over the sham-link. 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 the figure below) may exist. OSPF adjacency is established across the sham link. Cost of using 1 State POINT_TO_POINT. *> 10.0.0.0 0.0.0.0 0 32768 ? IGP Associate the However if there happens to be a OSPF neighborship between the two CEs then the traffic would directly flow across the directly connected link between the two CEs ignoring the path via MPLS VPN backbone which will act only as a backup in this case. the IP address of the loopback interface on PE-2. *>i 10.0.0.0 192.168.10.1 0 100 0 ? ospf Displays information about how the sham-link is advertised as an unnumbered point-to-point connection between two PE routers. Router2(config-if)# Use these resources to install and configure the software and to troubleshoot and resolve technical issues with Cisco products and technologies. loopback interface with a VRF. The OSPF costs If no backdoor link exists between the sites, no sham-link is required. MPLS The metric is used on the remote PE routers to select the correct route. The figure below shows an example of how VPN client sites that run OSPF can connect over an MPLS VPN backbone. Configuration for IOS XE and IOS XR as below IOS XE Sham-Link Configuration router ospf 100 vrf A The Cisco Support and Documentation website provides online resources to download documentation, software, and tools. When a sham-link is configured between PE routers, the PEs can populate the VRF routing table with the OSPF routes learned over the sham-link. Other thing to remember is that those loopbacks must be advertised by a protocol other than OPSF. If you've already registered, sign in. area <area-id> sham-link <source-address> <destination-address> cost <cost> from OSPF router configuration mode. Creates a loopback interface to be used as the endpoint of the sham-link on PE-2 and enters interface configuration mode. View this content on Cisco.com. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. Bug Search Tool and the In an MPLS VPN configuration, the OSPF protocol is one way you can connect customer edge (CE) routers to service provider edge (PE) routers in the VPN backbone. address for other sham-links. configure 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. Displays information about how the sham-link is advertised as an unnumbered point-to-point connection between two PE routers. As shown in Figure 4-53, CE1 and CE2 belong to the same OSPF area of VPN1 and they connect to PE1 and PE2 respectively. What is MPLS Label distributing protocol (LDP) ? undo arp learning passive enable Passive ARP. . Because each site runs OSPF within the same Area 1 configuration, all routing between the three sites follows the intraarea path across the backdoor links, rather than over the MPLS VPN backbone. Sham link configuration example. PE-1 and enters interface configuration mode. Assign area IDs to be associated with the range of IP addresses. loopback The sham link is a logical link, similar to a virtual link. vrf-name, 14. (PE routers advertise OSPF routes learned over the VPN backbone as interarea paths.) The following example shows BGP routing table entries for the prefix 10.3.1.7/32 in the PE-1 router in the figure above. Configures A sham-link overcomes the OSPF default behavior for selecting an intra-area backdoor route between VPN sites instead of an interarea (PE-to-PE) route. Transmitting Multi-Protocol Local Network Data Through a GRE Tunnel, Enlarging the Operation Scope of a Network with a Hop Limit, Building a Virtual Layer 2 Network Using Ethernet over GRE, Using Ethernet over GRE to Enable Layer 2 Communication Between an AC and a Wireless Gateway, Licensing Requirements and Limitations for GRE, Configuring a Route on a Tunnel Interface, (Optional) Configuring a Security Mechanism for GRE, Configuring Basic Ethernet over GRE Functions, (Optional) Configuring Ethernet over GRE Reliability, Collecting and Viewing Statistics on Tunnel Interfaces, Resetting Keepalive Packet Statistics on a Tunnel Interface, Example for Configuring a Static Route for GRE to Implement Interworking Between IPv4 Networks, Example for Configuring OSPF for GRE to Implement Interworking Between IPv4 Networks, Example for Enlarging the Operation Scope of a Network with a Hop Limit, Example for Connecting a CE to a VPN Through a GRE Tunnel over a Public Network, Example for Connecting a CE to a VPN Through a GRE Tunnel over a VPN, Example for Configuring Ethernet over GRE to Build a Virtual Layer 2 Network, Example for Configuring Ethernet over GRE to Enable Layer 2 Communication Between an AC and a Wireless Gateway, The Local Tunnel Interface Fails to Ping the IP Address of the Remote Tunnel Interface, Secure LAN Interconnection Through Efficient VPN, Licensing Requirements and Limitations for IPSec, Configuring an IPSec Session for Encryption, Establishing an IPSec Tunnel Using an Efficient VPN Policy, Verifying the Efficient VPN Configuration, Example for Establishing an IPSec Tunnel Using an Efficient VPN Policy in Client Mode, Example for Configuring an IPSec Tunnel Using an Efficient VPN Policy in Network Mode, Example for Configuring an IPSec Tunnel Using an Efficient VPN Policy in Network-Plus Mode, Application Scenarios for BGP/MPLS IP VPN, Interconnection Between VPNs and the Internet, Summary of BGP/MPLS IP VPN Configuration Tasks, Licensing Requirements and Limitations for BGP/MPLS IP VPN, Configuring Basic BGP/MPLS IP VPN Functions, Summary of Basic BGP/MPLS IP VPN Configuration Tasks, Establishing MP-IBGP Peer Relationships Between PE Devices, Configuring a VPN Instance on a PE Device, Configuring Route Exchange Between PE and CE Devices, Verifying the Configuration of Basic BGP/MPLS IP VPN Functions, Configuring MP-IBGP Between Hub-PE and Spoke-PE, Configuring Route Exchange Between PE device and CE Devices, Verifying the Hub and Spoke Configuration, Configuring Mutual Access Between Local VPNs, (Optional) Enabling Direct ARP Entry Delivery, Verifying the Configuration of Mutual Access Between Local VPNs, Configure Route Exchange Between an MCE Device and VPN Sites, Configure Route Exchange Between an MCE Device and a PE Device, Configuring Route Reflection to Optimize the VPN Backbone Layer, Configuring the Client PEs to Establish MP IBGP Connections with the RR, Configuring the RR to Establish MP IBGP Connections with the Client PEs, Configuring Route Reflection for BGP IPv4 VPN Routes, Verifying the Configuration of Route Reflection to Optimize the VPN Backbone Layer, Configuring and Applying a Tunnel Selector, Verifying Network Connectivity and Reachability, Viewing the Integrated Route Statistics of IPv4 VPN Instances, Resetting BGP Statistics of a VPN Instance IPv4 Address Family, Monitoring the Running Status of VPN Tunnels, Configuration Examples for BGP/MPLS IP VPN, Example for Configuring BGP/MPLS IP VPNs with Overlapping Address Spaces, Example for Configuring Communication Between Local VPNs, Example for Configuring Inter-AS VPN Option A, Example for Configuring an OSPF Sham Link, Example for Configuring BGP AS Number Substitution, Example for Configuring IP FRR for VPN Routes, Example for Configuring IP+VPN Hybrid FRR, Example for Configuring Double RRs to Optimize the VPN Backbone Layer, Example for Connecting a VPN to the Internet, Example for Configuring a Tunnel Policy for an L3VPN, Licensing Requirements and Limitations for BGP/MPLS IPv6 VPN, Summary of Basic BGP/MPLS IPv6 VPN Configuration Tasks, Establishing MP-IBGP Peer Relationships Between PEs, Configuring Route Exchange Between PEs and CEs, Verifying the Configuration of Basic BGP/MPLS IPv6 VPN Functions, Configuring Route Exchange Between the PE and CE, Configuring Route Reflection for BGP VPNv6 Routes, Configuring All Client PEs to Establish IBGP Connections with the RR, Configuring the RR to Establish MP-IBGP Connections with All Client PEs, Configuring Route Reflection for the Routes of the BGP VPN Instance, Verifying the Configuration of Route Reflection for BGP VPNv6 Routes, Monitoring the Running Status of BGP/MPLS IPv6 VPN, Verifying the Network Connectivity and Reachability, Viewing the Integrated Route Statistics of all VPN instances IPv6 address family, Resetting BGP Statistics of VPN instance IPv6 address family, Configuration Examples for BGP/MPLS IPv6 VPN, Example for Configuring Basic BGP/MPLS IPv6 VPN, Example for Configuring Hub and Spoke (Using BGP4+ Between the PE and CE), Example for Configuring Hub and Spoke (Using a Default Route Between Hub-PE and Hub-CE), Example for Configuring Inter-AS IPv6 VPN Option A, Example for Configuring an MCE IPv6 Device, Point-to-Point Layer 2 Connection Between Sites in Different Cities, Multi-service Transparent Transmission over PWs on a MAN, Licensing Requirements and Limitations for VLL, Configuring L2VPN Information Exchange Between the PE Devices, Configuring L2VPN Instances on PE Devices, (Optional) Configuring Route Reflection for BGP L2VPN, (Optional) Configuring Physical Layer Fault Notification, (Optional) Configuring a Revertive Switchover Policy, Enabling the VLL Traffic Statistics Collection Function, Example for Configuring a Local CCC Connection, Example for Configuring a Remote CCC Connection, Example for Configuring a VLL Connection in SVC Mode, Example for Configuring a VLL Connection in Martini Mode, Example for Configuring a Local VLL Connection in Kompella Mode, Example for Configuring a Remote VLL Connection in Kompella Mode, Example for Configuring a VLL Using an MPLS TE Tunnel, Example for Configuring Inter-AS Martini VLL (Option A), Example for Configuring Inter-AS Kompella VLL (Option A), Example for Configuring Martini VLL FRR (Asymmetrically Connected CEs), The VC of a Martini VLL Connection Cannot Go Up. cost number configures the OSPF cost for sending an IP packet on the PE-2 sham-link interface. Timer intervals configured, Hello 10, Dead 40, Wait 40, Index 2/2, retransmission queue length 0, number of retransmission 0, Last retransmission scan length is 0, maximum is 0, Last retransmission scan time is 0 msec, maximum is 0 msec, Sham Link OSPF_SL0 to address 111.5.5.5 is up. All rights reserved. Configures the sham-link on the PE-2 interface within a specified OSPF area and with the loopback interfaces specified by the IP addresses as endpoints. interface The syntax to configure sham-link is. An advanced Layer 3 IP switching technology. If no backdoor link exists between sites in the same area, you do not need to configure any OSPF sham link. Tell OSPF which interfaces we want to include. Router1(config)# Removes the IP address. ip You can see that Emerging industry standard upon which tag switching is based. Examples of common IGPs include IGRP, OSPF, and RIP. Use Cisco Feature A commonly used In an MPLS VPN configuration, the OSPF protocol is one way you can connect customer edge (CE) routers to service provider edge (PE) routers in the VPN backbone. OSPF STATE STUCK MTU MISMATCH. Creates a source-address An account on Cisco.com is not required. The command output shows that the neighbor relationship is in Full state. CEF optimizes network performance and scalability for networks with large and dynamic traffic patterns. Interdomain routing protocol that exchanges reachability information with other BGP systems. Some functions of the website may be unavailable. Interdomain routing protocol that exchanges reachability information with other BGP systems. This link is called a sham-link. - Rashmi Bhardwaj (Author/Editor), For Sponsored Posts and Advertisements, kindly reach us at: ipwithease@gmail.com, Routing entry for 9.9.0.5/32Known via ospf 1, distance 110, metric 3, type inter area, Type escape sequence to abort.Tracing the route to 9.9.0.5, Routing entry for 9.9.0.5/32Known via ospf 1, distance 110, metric 2, type intra area, router ospf 1 vrf shamlinkarea 0 sham-link 2.2.2.2 4.4.4.4 cost 1, Sham Link OSPF_SL0 to address 4.4.4.4 is up, BGP routing table entry for 2:2:9.9.0.1/32, version 61, Copyright AAR Technosolutions | Made with in India, How to Replace a vEdge Router via vManage: Cisco Viptela SDWAN, Salesforce Security Best Practices for Keeping Your Data Protected, Technology in the Medical Field to Look Out for in 2023, What is DDoS Attack? Configure OSPF on CE1, Switch, and CE2 and advertise the network segment of each interface. After entering these commands we will see a warning from R4. The OSPF intra-area path is preferred over the interarea path (over the MPLS VPN backbone) generated by the PE-1 router. The LSA contains information about neighbors and path costs and is used by the receiving router to maintain a routing table. CEF loopback interfaces specified by the IP addresses as endpoints. Before you create a A secure IP-based network that shares resources on one or more physical networks. I developed interest in networking being in the company of a passionate Network Professional, my husband. Router (config)# router ospf process_ID Router (config-router)# network IP_network_# [wild card mask] Area Number area number. --link-state advertisement. to avoid loops, ensure that all connected interfaces have STP disabled Configures A VPN contains geographically dispersed sites that can communicate securely over a shared backbone. r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter. configures the OSPF cost for sending an IP packet on the PE-1 sham-link For a sham link to be active, two conditions must be met: src-address is a valid local address with /32 netmask in OSPF instance's routing table. The MPLS VPN superbackbone provides an additional level of routing hierarchy to interconnect the VPN sites running OSPF. Router1(config-if)# ip vrf forwarding vrf-name, 6. If STP is enabled After the configuration is complete, run the display ip routing-table vpn-instance command on the PEs. --Open Shortest Path First protocol. how to configure OSPF Sham Links? Associates the How to configure MPLS L3 VPN with EIGRP ? All VPN processing occurs in the PE router. forwarding OSPF sham-links correct this behavior. --Open Shortest Path First protocol. In response to Arun Nair. To find information about Sending 5, 100-byte ICMP Echos to 192.168.40.1, timeout is 2 seconds: Success rate is 100 percent (5/5), round-trip min/avg/max = 44/72/104 ms. Sending 5, 100-byte ICMP Echos to 192.168.50.1, timeout is 2 seconds: Success rate is 100 percent (5/5), round-trip min/avg/max = 104/144/248 ms, BGP table version is 7, local router ID is 192.168.33.1, Route Distinguisher: 500:1 (default for vrf A-2). Associates the For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. caveats and feature information, see Configure an OSPF sham link between PE 1 and PE 2 so traffic between the CEs is forwarded through the MPLS backbone instead of the backdoor link. www.cisco.com/go/cfn. forwarding An Internet protocol used to exchange routing information within an autonomous system. mask, 10. Figure 4-53 Networking diagram for configuring an OSPF sham link Configuration Roadmap The configuration roadmap is as follows: Establish an ME-IBGP peer relationship between the PEs and configure OSPF between the PEs and CEs. However, as shown in bold in the next example, the VRF routing table shows that the selected path is learned via OSPF with a next hop of 10.2.1.38, which is the Vienna CE router. R4 (config-router)# redistribute eigrp 1. basic bgp configuration # config router bgp set as 65100 set router-id 172.16.1.3 config neighbor edit "10.3.1.254" set remote-as 65200 next end config network edit 1 set prefix 10.1.0.0 255.255.255. protocol redistribution . loopback --VPN routing and forwarding instance. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature. What is MPLS Label distributing protocol (LDP) ? CEF optimizes network performance and scalability for networks with large and dynamic traffic patterns. An account on Cisco.com is not required. A VPN client has three sites, each with a backdoor link. As a result, Removes the IP address. sham-linksource-address How LDP works? process-id No new or modified MIBs are supported by this feature. --Virtual Private Network. It is defined in RFC 1163. The PE router uses the information received from MP-BGP to set the ongoing label stack of incoming packets, and to decide to which egress PE router to label switch the packets. If the backdoor links between sites are used only for backup purposes and do not participate in the VPN service, then the default route selection shown in the preceding example is not acceptable. router Navigator to find information about platform support and Cisco software image LSA R4(config-if)#ip address 30.1.1.2 255.0.0.0, R4(config-if)#ip address 192.168.40.1 255.255.255.0, R5(config-if)#Ip address 10.1.1.2 255.0.0.0, R5(config-if)#Ip address 192.168.50.1 255.255.255.0, R1#show ip interface briefInterface IP-Address OK? address A broadcast packet used by link-state protocols. Configure VPN instances on PEs and bind the interfaces connected to CEs to the VPN instances. sham-link Version:V200R020C10.null. I am a biotechnologist by qualification and a Network Enthusiast by interest. This video demonstrates configuration a DMVPN Hub and Spoke in Phase 3 Configuration.It confirms Phase 3 connectivity between 2 Spokes and Hub to Spoke Conf. Procedure Configure an endpoint address for the sham link. cost number configures the OSPF cost for sending an IP packet on the PE-1 sham-link interface. which each feature is supported, see the feature information table. Distributed Denial of Service Attack, BGP NEIGHBORSHIP DROPS WHEN NAT IS ENABLED, VPRN Guide 2021 VIRTUAL PRIVATE ROUTED NETWORK. When the sham link is active, hello packets are . These customer edge (CE) routing devices are linked together by a Layer 3 VPN over Router PE1 and Router PE2. Creates a Using Distribute-List, OSPF Limit on Number of Redistributed Routes, OSPFv3 Fast Convergence: LSA and SPF Throttling, OSPF Support for Unlimited Software VRFs per PE Router, OSPF Link-State Database Overload Protection, OSPF MIB Support of RFC 1850 and Latest Extensions, Configuring OSPF TTL Security Check and OSPF Graceful Shutdown, OSPF SNMP ifIndex Value for Interface ID in Data Fields, OSPF Support for Forwarding Adjacencies over MPLS TE Tunnels, OSPF IPv4 Remote Loop-Free Alternate IP Fast Reroute, Prerequisites for OSPF Sham-Link Support for MPLS VPN, Restrictions on OSPF Sham-Link Support for MPLS VPN, Information About OSPF Sham-Link Support for MPLS VPN, Benefits of OSPF Sham-Link Support for MPLS VPN, Using a Sham-Link to Correct OSPF Backdoor Routing, Configuration Examples of an OSPF Sham-Link, Example Sham-Link Between Two PE Routers, Feature Information for OSPF Sham-Link Support for MPLS VPN. % Only classful networks will be redistributed. Configures the number 2022 Cisco and/or its affiliates. Sham Linkcan be created using two loopbacks on the respective devices advertised into the BGP address family that corresponds with the customerVRF. In some cases where Providers deliverMPLSlinks to customer locations ,OSPFmay be used asCE-PErouting protocol. The PE router also uses the information received from MP-BGP to set the outgoing label stack of incoming packets, and to decide to which egress PE router to label switch the packets. I tested R8 and R6 after reboot. To reestablish the desired path selection over the MPLS VPN backbone, you must create an additional OSPF intra-area (logical) link between ingress and egress VRFs on the relevant PE routers. --Interior Gateway Protocol. They are deployed in cases when areas become partitioned or an area does not border Area 0. sham-link with an existing OSPF area. may not support all the features documented in this module. Creating the VPN Interface Template for the TLOC-EXT interface. You can search by feature or release. What they are, how they work, and why we need them. For this reason, you should not modify the metric value when OSPF is redistributed to BGP, and when BGP is redistributed to OSPF. A router that is part of a customer network and that interfaces to a provider edge (PE) router. In general, a VRF includes the routing information that defines a customer VPN site that is attached to a PE router. In an MPLS VPN configuration, the OSPF protocol is one way you can connect customer edge (CE) routers to service provider edge (PE) routers in the VPN backbone. However, as shown in bold in the next example, the VRF routing table shows that the selected path is learned via OSPF with a next hop of 10.2.1.38, which is the Vienna CE router. Device(config-router-af)# area 1 virtual-link 1.1.1.1 authentication key-chain ospf-chain-1: Configures the authentication for virtual links. For these steps following commands are used respectively. Configures The PE router can then flood LSAs between sites from across the MPLS VPN backbone. The PE routers that attach to the VPN use the Border Gateway Protocol (BGP) to distribute VPN routes to each other. lets see the configuration for better understanding:-, R1(config-if)#Ip address 10.1.1.1 255.0.0.0, R1(config-if)#Ip address 1.1.1.1 255.0.0.0, R1(config-if)#Ip address 3.3.3.2 255.0.0.0, R1(config-if)#Ip address 192.168.10.1 255.255.255.0, R1(config-if)#Ip address 192.168.11.1 255.255.255.0, R1(config-if)#Ip address 192.168.12.1 255.255.255.0, R1(config-if)#Ip address 192.168.13.1 255.255.255.0, R2(config-if)#Ip address 20.1.1.1 255.0.0.0, R2(config-if)#Ip address 1.1.1.2 255.0.0.0, R2(config-if)#Ip address 2.2.2.1 255.0.0.0, R2(config-if)#Ip address 192.168.20.1 255.255.255.0, R2(config-if)#Ip address 192.168.21.1 255.255.255.0, R2(config-if)#Ip address 192.168.22.1 255.255.255.0, R2(config-if)#Ip address 192.168.23.1 255.255, R3(config-if)#Ip address 30.1.1.1 255.0.0.0, R3(config-if)#Ip address 2.2.2.2 255.0.0.0, R3(config-if)#Ip address 3.3.3.1 255.0.0.0, R3(config-if)#Ip address 192.168.30.1 255.255.255.0, R3(config-if)#Ip address 192.168.31.1 255.255.255.0, R3(config-if)#Ip address 192.168.32.1 255.255.255.0. interface. (PE routers advertise OSPF routes learned over the VPN backbone as interarea paths.) Further, routes reach the remote CE after being redistributed from BGP into OSPF process running between CE and PE for a specific VRF. The LSA contains information about neighbors and path costs and is used by the receiving router to maintain a routing table. A sham-link is required between any two VPN sites that belong to the same OSPF area and share an OSPF backdoor link. The figure below shows a sample sham-link between PE-1 and PE-2. 2022 Cisco and/or its affiliates. --provider edge router. The metric is used on the remote PE routers to select the correct route. Router2(config)# cost Cost of the OSPF route from CE1 to CE2 = Cost of the path from CE1 to PE1 + Cost of the sham link + Cost of the path from PE2 to CE2 = 1 + 1 + 1 = 3. The following output shows the forwarding that occurs between sites from the standpoint of how PE-1 views the 10.3.1.7/32 prefix, the loopback1 interface of the Winchester CE router in the figure. View with Adobe Reader on a variety of devices. A sham-link ensures that OSPF client sites that share a backdoor link can communicate over the MPLS VPN backbone and participate in VPN services. OSPF Sham links is a logical inter-area link carried by the super backbone. OSPF Update Packet-Pacing Configurable Timers, OSPF Forwarding Address Suppression in Translated Type-5 LSAs, OSPF Inbound Filtering Using Route Maps with a Distribute List, OSPFv3 Fast Convergence: LSA and SPF Throttling, OSPF Mechanism to Exclude Connected IP Prefixes from LSA Advertisements, OSPF Limit on Number of Redistributed Routes, OSPF Support for Unlimited Software VRFs per PE Router, OSPF Link-State Database Overload Protection, OSPF MIB Support of RFC 1850 and Latest Extensions, OSPF Support for Forwarding Adjacencies over MPLS TE Tunnels, Configuring OSPF TTL Security Check and OSPF Graceful Shutdown, Area Command in Interface Mode for OSPFv2, OSPFv3 IPSec ESP Encryption and Authentication, IPv6 Routing: OSPFv3 Authentication Support with IPsec, Using a Sham-Link to Correct OSPF Backdoor Routing. Run the display ip routing-table command on a CE, and you can see that the cost of the OSPF route to the remote CE has changed to 3, and the next hop has changed to the VLANIF interface connected to the PE. DoNotAge LSA allowed. An error occurred when loading the video. A router that is part of a service provider network connected to a customer edge (CE) router. For the latest vrf-name, 12. router To verify that the sham-link was successfully created and is operational, use the show ip ospf sham-links command in EXEC mode: Displays the operational status of all sham-links configured for a router. Passive ARPVRRPBackupIP . Enters global configuration mode on the second PE router. the features documented in this module, and to see a list of the releases in S1720, S2700, S5700, and S6720 V200R011C10. Because the sham-link is seen as an intra-area link between PE routers, an OSPF adjacency is created and database exchange (for the particular OSPF process) occurs across the link. For the latest The following example shows BGP routing table entries for the prefix 10.3.1.7/32 in the PE-1 router in the figure above. This table lists only the software release that introduced support for a given feature in a given software release train. interface-number, 8. The section, "Creating a Sham-Link", describes how to configure a sham-link between two PE routers. As a result, the desired intra-area connectivity is created. Pre-configuration Tasks. router Before you can configure a sham-link in an MPLS VPN, you must first enable OSPF as follows: Specify the range of IP addresses to be associated with the routing process. In the following example, PE-2 shows how an MP-BGP update for the prefix is not generated. The OSPF sham-link is used only to influence intra-area path selection. Configuring OSPF sham links Network requirements As shown in Figure 46: CE 1 and CE 2 belong to VPN 1 and are connected to PE 1 and PE 2, respectively. vrf-name, 9. OSPF has a lower administrative distance (AD) than internal BGP (BGP running between routers in the same autonomous system). Configure one serial link (backup link /backdoor) between router 4/5. vrf-name, 4. To obtain lists of supported MIBs by platform and Cisco IOS release, and to download MIB modules, go to the Cisco MIB website on Cisco.com at the following URL: http://www.cisco.com/public/sw-center/netmgmt/cmtk/mibs.shtml. 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. When OSPF is used as a protocol between PE and CE routers, the OSPF metric is preserved when routes are advertised over the VPN backbone. Now to overcome this behaviour we will configure OSPF Sham Link between PE1 and PE2 & then see the behaviour. A VPN contains geographically dispersed sites that can communicate securely over a shared backbone. To create a sham-link, use the following commands starting in EXEC mode: 2. --Multiprotocol Label Switching. When the backdoor link is not enabled between the CE1 and CE2 the path followed from CE1 to CE2 is via MPLS backbone as shown below , Last update from 9.9.12.2 on FastEthernet0/0, 00:00:10 ago, * 9.9.12.2, from 9.9.12.2, 00:00:10 ago, via FastEthernet0/0 #Known via R2#, Route metric is 3, traffic share count is 1, VRF info: (vrf in name/id, vrf out name/id), 2 9.9.23.3 [MPLS: Labels 17/16 Exp 0] 96 msec 56 msec 76 msec, 3 9.9.45.4 [MPLS: Label 16 Exp 0] 84 msec 80 msec 56 msec. This example is designed to show how a sham-link is used only to affect the OSPF intra-area path selection of the PE and CE routers. Before you can configure a sham-link in an MPLS VPN, you must first enable OSPF as follows: Specify the range of IP addresses to be associated with the routing process. For basic information about how to configure an MPLS VPN, refer to the OSPF Sham links are used in MPLS VPNs using OSPF where both sites have a backdoor link and routing preference should be given to the MPLS path instead of backdoor link. # rip 1 version 2 network 192.168.1. network 12.0.0.0 AR2 ip vpn-instance a - incomplete, RPKI validation codes: V valid, I invalid, N Not found, Network Next Hop Metric LocPrf Weight Path, Route Distinguisher: 500:1 (default for vrf A-1). Method Status ProtocolFastEthernet0/0 10.1.1.1 YES manual up upSerial4/0 1.1.1.1 YES manual up upSerial4/2 3.3.3.2 YES manual up upLoopback0 192.168.10.1 YES manual up upLoopback1 192.168.11.1 YES manual up upLoopback2 192.168.12.1 YES manual up upLoopback3 192.168.13.1 YES manual up up, Interface IP-Address OK? Figure 46: Network diagram Customers Also Viewed These Support Documents. Enable OSPF routing protocol from global configuration mode. Router1(config)# The PE router also uses the information received from MP-BGP to set the outgoing label stack of incoming packets, and to decide to which egress PE router to label switch the packets. Establish an ME-IBGP peer relationship between the PEs and configure OSPF between the PEs and CEs. To verify that the sham-link was successfully created and is operational, use the show ip ospf sham-links command in EXEC mode: Displays the operational status of all sham-links configured for a router. The area_id is the " transit area " that OSPF will tunnel through. 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. The only entry within the BGP table is the MP-BGP update received from PE-3 (the egress PE router for the 10.3.1.7/32 prefix). Run the display ospf routing command on the CEs. PE A sham-link overcomes the OSPF default behavior for selecting an intra-area backdoor route between VPN sites instead of an interarea (PE-to-PE) route. ip Otherwise, register and sign in. to the remote CE is forwarded through the backbone network. terminal, 7. To find information about Bug Search Tool and the This module describes how to configure and use a sham-link to connect Virtual Private Network (VPN) client sites that run the Open Shortest Path First (OSPF) protocol and share backdoor OSPF links in a Multiprotocol Label Switching (MPLS) VPN configuration. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. To access Cisco Feature Navigator, go to A Sham links is required only between two VPN sites that belong to the same area and have a backdoor link for backup purposes. 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. The "transit area" cannot . 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