All routing neighbors are available when verified from the device via CLI or GUI. The only way to fix this is to advertise the routes that are learned through the MPLS VPN network as intra-area routes. 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. No new or modified RFCs are supported by this feature. Service Provider Certifications. You dont have to configure anything on the CE routers. All Tags. The OSPF intra-area path is preferred over the interarea path (over the MPLS VPN backbone) generated by the PE-1 router. Figure4 shows a sample MPLS VPN topology in which a sham-link configuration is necessary. You need to setup a sham-link if you want the traffic between the two sites to prefer the mpls backbone rather than the backdoor link. The OSPF database shows that the other customer site are inter-area router. Flexible Routing in an MPLS VPN Configuration Want to take a look for yourself? Cisco Feature Navigator is a web-based tool that enables you to quickly determine which Cisco IOS software images support a specific set of features and which features are supported in a specific CiscoIOS image. Router#show ip ospf data router ip-address. R5(config)#int ser 0/1.15 Test and Explore your knowledge. Mpls Layer 3 VPN Pe-ce Ospf Sham Link. For this reason, OSPF backdoor links between VPN sites must be taken into account so that routing is performed based on policy. A Sham links is required only between two VPN sites that belong to the same area and have a backdoor link for backup purposes. A broadcast packet used by link-state protocols. 172.16.0.0/24 is subnetted, 1 subnets Ask a question or join the discussion by visiting our Community Forum, Get Full Access to our 751 Cisco Lessons Now, O 5.5.5.5 [110/101] via 192.168.15.5, O 1.1.1.1 [110/101] via 192.168.15.1, Unit 2: LDP (Label Distribution Protocol), MPLS L3 VPN PE-CE OSPF Global Default Route, MPLS Traffic Engineering (TE) IS-IS Configuration, MPLS TE Fast Reroute Path Link Protection. 172.16.0.0/24 is subnetted, 1 subnets There is no default. Creates a loopback interface to be used as the endpoint of the sham-link on PE-2 and enters interface configuration mode. These links are able to fool/trick routers in the OSPF domain that this is a better path thus preserving the LSAs as type 1 or type 3. By default bgp learned routes do not get a label assigned (only the next hop). The next example shows forwarding information in which the next hop for the route, 10.3.1.2, is the PE-3 router rather than the PE-2 router (which is the best path according to OSPF). To correct this default OSPF behavior in an MPLS VPN, use the area sham-link cost command to configure a sham-link between two PEs to connect the sites through the MPLS VPN backbone. This blog post walks through the problem and the solution, including the configuration steps to create and verify a sham-link. All other commands used with this feature are documented in the Cisco IOS Release 12.2 command reference publications. If no backdoor link exists between the sites, no sham-link is required. To create a sham-link, use the following commands starting in EXEC mode: Enters global configuration mode on the first PE router. ", describes how to configure a sham-link between two PE routers. What they are, how they. Keywords: Routing, Switching, Wifi, Cisco, Meraki, Cisco ISE, Check Point, OSPF, BGP, MPLS, ITIL, Azure Networking, ExpressRoute, SD-WAN, Palo Alto, Peering. All logos, trademarks and registered trademarks are the property of their respective owners. f OSPF Sham-Link Support for MPLS VPN Feature Overview Feature Overview Using OSPF in PE-CE Router Connections 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. The OSPF sham link provides a logical link between two VRFs. O 10.12.0.0 [110/65] via 10.15.0.1, 00:03:19, Serial0/1.15, Notice, that the remote customer networks attached to Fa0/0 and Fa0/1 are now reachable via the serial 0/1.15 interface, and they appear as Intra-Area routes. This means upon redistribution out of BGP into OSPF, routes retain their external route marking. R4(config-router)#area 1 sham-link 11.11.11.4 11.11.11.2 cost 5 Looks like it is in place, but is it creating the desired result, of having the CE routers R1 and R5 see the Ethernet remote networks as reachable through the PE routers R2 and R4? OSPF running on a PE device can use the routing information to generate inter-area routes from the PE to CE devices. Router1(config)# router ospf process-id vrf vrf-name. IP address of the source PE router in the format: ip-address [mask]. Configures the specified OSPF process with the VRF associated with the sham-link interface on PE-1 and enters interface configuration mode. This says to me that the sham-link CANNOT be lable switched throughout the core network. Examples of common IGPs include IGRP, OSPF, and RIP. Otherwise the routes learnt via the mpls backbone will be seen as inter-area at best and traffic will be forwarded via the backdoor as routes learnt via the backdoor are seen as intra-area and therefore preferred Great Courses, Lessons and Learning Material. This takes less than ~50 ms. 10.0.0.0/24 is subnetted, 3 subnets A VRF consists of an IP routing table, a derived forwarding table, a set of interfaces that use the forwarding table, and a set of rules and routing protocols that determine what goes into the forwarding table. OSPF will always prefer an intra area route over an inter area route, this is regardless of the metric that is associated with that route. Notice that the Sham-links have been advertised through as a Type 5 external LSA link type. LSAlink-state advertisement. Open navigation menu. !!!!! The OSPF sham-link is used only to influence intra-area path selection. 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. To access Cisco Feature Navigator, you must have an account on Cisco.com. So a sham link does more than create a link between loopbacks. 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. OSPF Sham links is a logical inter-area link carried by the super backbone. To avoid such a problem, an OSPF sham link can be established between PEs so that the routes that pass through the MPLS VPN backbone network also become OSPF intra-area routes and take precedence. Expert in low latency network technologies - Including Multicast (IGMP, PIM), L2 /L3, WAN Design, expert in routing (BGP, OSPF ) Minimum of 10 years of experience in a network engineering, operations, and support. CE routercustomer edge router. The Sham-link Endpoint Address must be advertised by BGP as VPN-IPv4 address; it must NOT be advertised by OSPF. The sham link is advertised using Type 1 link-state advertisements (LSAs). Notice that R1 and R5 can see each others Fa0/0 and Fa0/1 connected networks. It creates a link that makes the MPLS PEs participating in the sham link appear as a point to point link within OSPF. OSPF creates an adjacency and exchanges LSAs across the sham link. 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. Reconfigures the IP address of the loopback interface on PE-1. Presented to you by instructor Rene Molenaar, CCIE #41726. I still love it when a plan comes together. This is due to no longer being an external route and becoming an intra-area route. Although 10.3.1.7/32 has been learned via OSPF across the sham-link as shown in bold, no local generation of a route into BGP is performed. All Webinars & Events. R4(config-if)#router bgp 24 For this reason, you should not modify the metric value when OSPF is redistributed to BGP, and when BGP is redistributed to OSPF. If these sites are connected over a backdoor link in addition to the VPN backbone, all traffic passes over the backdoor link instead of over the VPN backbone. Each task in the list is identified as either required or optional. The networks from the other customer site are passed over this OSPF sham link as Type 1 router LSA. When the primary LSP is broken, we can continue to forward traffic down the backup tunnel until the headend router figures out a new best path. Currently, R1 and R5 see the routes to each others local networks through the VPNv4 MPLS network, and the routes show up as Inter-Area OSPF routes with the PE routers as the next hop. Across the sham link, the PE routers can build an OSPF adjacency directly with each other. Interdomain routing protocol that exchanges reachability information with other BGP systems. IS-IS Intermediate System-to-Intermediate System, ONLINE LABS---CCNP//CCNA// CISCO PIX ASA//LAYER-3 SWITCH, Virtual Community Study Group-------CCIE MODULES, X.Cisco Support--Documents and Discussion. 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. What is MPLS Label distributing protocol (LDP) ? Hence, the default Hello interval is 10 seconds and the default Router Dead interval is 40 seconds. If you have forgotten or lost your account information, send a blank e-mail to cco-locksmith@cisco.com. You can search by feature or release. The goal was to connect it over MPLS and leverage OSPF for the PE to CE connection. Open Shortest Pathway First ( OSPF ) is an Open Standard Link State routing protocol. OSPF Open Shortest Path First (OSPF) is a link-state routing protocol that was developed for IP networks and is based on the Shortest Path First (SPF) algorithm. Configures the specified OSPF process with the VRF associated with the sham-link interface on PE-2 and enters interface configuration mode. The source and destination IP addresses must belong to the VRF and be advertised by Border Gateway Protocol (BGP) to remote PE routers. OSPFsham-linkintra-areaMPLS sham-link MPLS-PECEOSPFPECEVRFPEPECE CEbackdoor linkbackdoor linkMPLS CE1OSPFCE24.4.4.4/32CE14.4.4.4 Emerging industry standard upon which tag switching is based. The sham link is an unnumbered point-to-point link inside a routing-instance between two PE routers. . By default, OSPF external routes dont get redistributed into BGP but you can change that. Well wait a few moments, to give the network time to converge, then take a look at the OSPF routes on the CE routers R1 and R5, just as we did earlier, and see if the routes are different. Configures the sham-link on the PE-1 interface within a specified OSPF area and with the loopback interfaces specified by the IP addresses as endpoints. Because the sham-link is seen as an Intra-Area link between PE routers (R2 and R4), an OSPF adjacency is created and database exchange takes place across the sham-link. Configures the sham-link on the PE-1 interface within a specified OSPF area and with the loopback interfaces specified by the IP addresses as endpoints. 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. CEF optimizes network performance and scalability for networks with large and dynamic traffic patterns. Rating: 4.7. Therefore they are marked as external routes and no longer preferred by OSPF. Apply Now Nezar Lourens The two PE routers can then flood LSAs between sites from across the MPLS VPN backbone. A sham-link is required between any two VPN sites that belong to the same OSPF area and share an OSPF backdoor link. A traceroute. R1 and R5 are Customer Edge (CE) routers, and the Serial0/1.15 interfaces of R1 and R5 are temporarily shut down, (this means the backdoor route isn't in place yet, and at the moment, there is no problem). It is not possible to route traffic from one sham-link over another sham-link. en Change Language. cost number configures the OSPF cost for sending an IP packet on the PE-1 sham-link interface. VPN. No new or modified MIBs are supported by this feature. Cisco Feature Navigator dynamically updates the list of supported platforms as new platform support is added for the feature. OSPF Sham-link Does anyone know exactly how the ospf sham-link operates. The LSA contains information about neighbors and path costs and is used by the receiving router to maintain a routing table. 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. This prefix is the loopback interface of the Winchester CE router. Failover approach, where a spoke has an active tunnel with one hub at any given point in time. configures the OSPF cost for sending an IP packet on the PE-2 sham-link interface. It confirms Phase 3 connectivity between 2 Spokes and Hub to Spoke Conf. It allows you to create a point-to-point connection between the two PE routers. SPARK: VMware PEX and I am presenting four sessions. OSPF sham-link host interfaces MUST be advertised by BGP and not the ospf process. (I dont think they will be providing a price break either). Top 13 Most Asked OSPF Interview Questions with Answers - Interview Preprations 1. As a result, the desired Intra-Area routes are created. Lets take a closer look at the sham link with a show command made just for that purpose. Router1(config)# interface loopback interface-number. OSPF always selects intra-area routes over interarea (external) routes. CE routers are not aware of associated VPNs. Lets do one more test to prove that as well. In the following example, PE-2 shows how an MP-BGP update for the prefix is not generated. cost number configures the OSPF cost for sending an IP packet on the PE-2 sham-link interface. data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAKAAAAB4CAYAAAB1ovlvAAAAAXNSR0IArs4c6QAAAnpJREFUeF7t17Fpw1AARdFv7WJN4EVcawrPJZeeR3u4kiGQkCYJaXxBHLUSPHT/AaHTvu . configures the OSPF cost for sending an IP packet on the PE-1 sham-link interface. 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. To train the network to use the MPLS network as the primary transit path, we need to make the remote Ethernet customer networks look like Intra-Area routes via the PE routers, with a better metric than the serial interfaces, so they can be used instead of the slower serial link. OSPF is an Interior Gateway Protocol (IGP). If a customers is using OSPF to peer between the CE and PE routers, and also has an OSPF CE to CE neighborship, the CE's will prefer the Intra-Area CE to CE routes (sometimes called the "backdoor" route in this situation), instead of using the Inter-Area CE to PE learned routes that use the MPLS network as a transit path. We are actually going to pull a fast one, or a sham, on OSPF because the MPLS network is really acting as a superbackbone for OSPF, and therefore routes between the CEs are indeed Inter-Area by default. To get updated information regarding platform support for this feature, access Cisco Feature Navigator. The section, "Creating a Sham-Link", describes how to configure a sham-link between two PE routers. When sending traffic to a particular destination, the PE router uses the MP-BGP forwarding information. Now the Service Providers MPLS network will only be used as a backup in the event the serial connection fails. Router2(config)# interface loopback interface-number. R5#show ip route ospf Next, we will enable the Serial0/1.15 interfaces of R1 and R5. Community Impact. R4(config)#int loop 100 Because the sham-link is seen as an Intra-Area link between PE routers (R2 and R4), an OSPF adjacency is created and database exchange takes place across the sham-link. Open shortest path first is an Open Standard Link State routing protocol which works by using Dijkastra algorithm to initially construct the shortest paths and follows that by populating the routing table with resulting best paths. Applicants are expected to participate in after-hours work and an on-call rotation. The sham link is established between two IP addresses that have to be in the VRF of the customer. An automatic check will verify that your e-mail address is registered with Cisco.com. This is due to no longer being an external route and becoming an intra-area route. For example, Figure2 shows three client sites, each with backdoor links. We have two sites connecting to each other via an MPLS cloud. I thought it would make a beneficial addition to our blog, and here it is. These routes show up as Inter-Area (IA) routes. R5(config-subif)#no shut. We can confirm that the backdoor link is routing all traffic by checking the OSPF route table. When an OSPF sham-link is set it builds a bridge between two VRF's. By advertising a type 1 LSA (Router) across this link, the OSPF database sees this route and the routes advertised across this link as acceptable. Ps. Thanks for the request Christian! 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). A sham-link between PE-1 and PE-3 is not necessary in this configuration because the Vienna and Winchester sites do not share a backdoor link. Router2(config-if)# area area-id sham-link source-address destination-address cost number. Sending 5, 100-byte ICMP Echos to 172.16.0.1, timeout is 2 seconds: The routing table indicates that we are learning the other sites routes via the MPLS cloud. area 120 sham-link 10.0.0.1 10.44.0.1 cost 1, network 10.120.0.0 0.255.255.255 area 120, network 10.140.0.0 0.255.255.255 area 120, area 120 sham-link 10.44.0.1 10.0.0.1 cost 1. Webinars & Videos. You only need a sham link when you have a backdoor link in between your CE routers. Enterprise Wireless Certification. We can do this with the OSPF sham link. R4(config-if)#ip vrf forwarding Vrf1 OSPF adjacency is established across the sham link. Proceeding to add a private link between the branch and HQ sites did I realise that OSPF no longer leveraged the MPLS cloud but used the private link. Thanks! 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. In an MPLS VPN configuration, the OSPF cost configured with a sham-link allows you to decide if OSPF client site traffic will be routed over a backdoor link or through the VPN backbone. In general, a VRF includes the routing information that defines a customer VPN site that is attached to a PE router. Within BGP, the locally generated route (10.2.1.38) is considered to be the best route. A VPN client has three sites, each with a backdoor link. September 13, 2017 MPLS 3 comments. VPNVirtual Private Network. What Is Ospf Routing Protocol? If the check is successful, account details with a new random password will be e-mailed to you. VRFVPN routing and forwarding instance. %OSPF-5-ADJCHG: Process 1, Nbr 10.12.0.2 on OSPF_SL0 from LOADING to FULL, Loading Done. sham-link VPNVPNOSPFVPNOSPF. 5. OSPF cost to send IP packets over the sham-link interface.Valid values are from 1 to 65535. The type 3 inter-area LSAs show network 5.5.5.5 and the uplink to the ISP, 192.168.35.0. We are looking for a Network Engineer with automation skills that is comfortable with taking ownership of network layers and infrastructure, someone that can design and provide expert driven solutions optimized for given constraints. OSPF knowledge is not required but being familiar with the basics of routing is recommended. By using two loopbacks on the respective devices advertised into the BGP address family that corresponds with the customer VRF, OSPF can create a link that is more appealing. The backdoor link becomes favoured and subsequently used. We will ping the remote Fa0/1 interface of CE router R1 from CE router R5. router ospf 1. vrf A. domain-id type 0005 value 000000010200. thanks! Sign in|Recent Site Activity|Report Abuse|Print Page|Powered By Google Sites. This articles discusses how to troubleshoot such issues. When we enable these interfaces, R1 and R5 will become neighbors, and see each others routes to the Fa0/0 and Fa0/1 networks as Intra-Area routes. As shown in bold in this example, the loopback interface is learned via BGP from PE-2 and PE-3. PE routerprovider edge router. As a result, the desired intra-area connectivity is created. This is the topology currently. CEFCisco Express Forwarding. The reason the OSPF route is not redistributed to BGP on the PE is because the other end of the sham-link already redistributed the route to BGP and there is no need for duplication. Experience with Arista, Cisco and L1 switches. In IE11, they show the text with scroll bars under each line of text? Looks like the sham-link came up. As expected a trace route results in: An MPLS link is not preferred in OSPF when there is a back door because intra-area routes are preferred over external routes. Client Site Connection Across the MPLS VPN Backbone. Type escape sequence to abort. 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. Removes the IP address. This was quite easy to do and very simple to manage. ;). For more information on these OSPF configuration procedures, go to: See the following sections for configuration tasks for the sham-link feature. To prevent the backbone network from being disconnected, a backdoor link is created between the site1 and site2, R5 and R7 . These links are able to fool or trick routers in the OSPF domain that this is a better path thus preserving the LSAs as type 1 or type 3. The PE router can then flood LSAs between sites from across the MPLS VPN backbone. A router that is part of a customer network and that interfaces to a provider edge (PE) router. OSPF sham-link cost. Notify me of follow-up comments by email. The example in this section 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. OSPF Sham Links are required when you try to use a backdoor link between two CE routers in an MPLS VPN PE CE scenario where you use OSPF as the PE-CE routing protocol. Thx. The Internet's global routing system is based on. OSPF Sham Links are required when we try to use a backdoor link between two CE routers in MPLS VPN PE CE scenarios. The /32 address must meet the following criteria: You can use the /32 address for other sham-links. R4(config-router-af)#exit close menu Language. What the different OSPF stub areas are and how they work. area area-id sham-link source-address destination-address cost number, no area area-id sham-link source-address destination-address cost number. Pretty cool. The Sham-link is an unnumbered point-to-point intra-area link and is advertised as Type-1 link in router-LSA. OSPF - NetworkLessons.com OSPF Course Description OSPF (Open Shortest Path First) is a popular link-state routing protocol. To achieve this, we will create a new loopback interface on each PE router which is advertised in BGP: Hi Rene, Mpls Layer 3 VPN Pe-ce Ospf Sham Link - Free download as PDF File (.pdf), Text File (.txt) or read online for free. Routers will exchange pieces of information called LSAs (link state advertisement) in order to build a complete topology database which we call the LSDB (link state database). OSPF Network Design Solutions (2nd Edition)One of my reader asked a question,"Normally customers require sham link to prefer back door link in case of MPLS VPN environment, when customer run same area. Reconfigures the IP address of the loopback interface on PE-2. R4(config-if)#ip address 11.11.11.4 255.255.255.255 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. R5#show ip route ospf What is Sham Link? Success rate is 100 percent (5/5), round-trip min/avg/max = 120/130/148 ms. Thats cool, so we know we have connectivity, and based on the routing table output, we believe it is going through the SP MPLS network. OSPF sham-link. Router1(config-if)# ip vrf forwarding vrf-name. Question 90: What does BADSEQNUM in the %OSPF-5-NBRSTATE: OSPF-101 [5330] Process 101, Nbr 10.253.5.108 on Vlan7 02 from FULL to EXSTART, BADSEQNUM OSPF log message mean?. 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. Generally, BGP peers use BGP extended community attributes to carry routing information over the MPLS VPN backbone. Post was not sent - check your email addresses! This is because OSPF always prefers intra-area routes over inter-area routes. When an OSPF sham-link is set it builds a bridge between two VRFs. 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. Lets increase the metric for our backdoor link to 100: Lets see which interface our CE routers now want to use: Despite the higher cost, CE1 and CE2 prefer the backdoor link. R4(config-router)#router ospf 1 vrf Vrf1 sham-link VPN sham-linkVPNVPNOSPFVPNOSPF VPN PEOSPF MPLS VPNOSPFVPN 32LoopbackLoopbackVPNBGP OSPFPE How LDP works? If there is a backdoor link between R4 and R5, traffic will be routed over that backdoor link rather than going through MPLS cloud. It is important to remember if you have a backdoor link that you should enable. Configure the source and destination addresses of the sham-link as a host route mask (255.255.255.255) on the PE routers that serve as the endpoints of the sham-link. kind of weird. Routes that are advertised across a MPLS/VPN that are imported and exported into BGP pass the route information with it. This command has no arguments or keywords. Security Certifications. Creates a loopback interface to be used as an endpoint of the sham-link on PE-1 and enters interface configuration mode. Valid values: numeric value or valid IP address. Heres a quick example: 5 more replies! Thats correct. Source: CCIE study: OSPF Sham . The following example shows BGP routing table entries for the prefix 10.3.1.7/32 in the PE-1 router in Figure2. The basics of link-state routing protocols and OSPF. A sham-link represents an intra-area (unnumbered point-to-point) connection between PEs. The following example 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 Figure4. Router1(config-if)# area area-id sham-link source-address destination-address cost number. Interesting post Anthony. The routing table as it currently stands shows OSPF advertising loopbacks from the Customer sites via the MPLS cloud. . This is best explained with an example, take a look at the following topology: Above we have an MPLS VPN topology where we use OSPF as the PE-CE routing protocol. To configure a sham-link interface on a provider edge (PE) router in a Multiprotocol Label Switching (MPLS) Virtual Private Network (VPN) backbone, use the area sham-link cost command in global configuration mode. (PE routers advertise OSPF routes learned over the VPN backbone as interarea paths.) When monitoring routing neighbors in the Orion platform, you may see the Routing Neighbors resource show no data when the device CLI and GUI is populated with OSPF and BGP routing neighbors. An OSPF sham-link can solve this problem. So lets now take a look at the Sham link adjusted OSPF database. Here is the routing table as it stands. View MPLS Layer 3 VPN PE-CE OSPF Sham Link _ NetworkLessons.com.pdf from COMPUTER 198 at Polytechnic University of the Philippines. An OSPF sham-link will have a default cost of 1 ensuring that it is chosen as the best path over alternative possible paths. To begin, MPLS is set up in the network as shown with R2 and R4 acting as Provider Edge (PE) routers, and MPLS is enabled throughout R2-R3-R4. Two sham-links have been configured, one between PE-1 and PE-2, and another between PE-2 and PE-3. And just to be sure, a ping to verify connectivity. Type escape sequence to abort. Cisco IOS Configuration Fundamentals Configuration Guide, Release 12.2, Cisco IOS Configuration Fundamentals Command Reference, Release 12.2, Cisco IOS IP Command Reference, Volume 2 of 3: Routing Protocols, Release 12.2, http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fiprrp_r/1rfospf.htm, http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft/120t/120t5/vpn.htm, http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfospf.htm, http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfbgp.htm, RFC 1164, Application of the Border Gateway Protocol in the Internet, RFC 2283, Multiprotocol Extensions for BGP-4, RFC 2328, Open Shortest Path First, Version 2, Determining Platform Support Through Cisco Feature Navigator. It is also generated through redistribution into BGP on PE-1. A cost is configured with each sham-link and is used to decide whether traffic will be sent over the backdoor path or the sham-link path. By using the commandarea
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ospf sham link network lessons
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