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642-845 – Optimizing Converged Cisco Networks – ONT
She is responsible for designing and implementing data and VoIP networks, supporting companies based in the National Capital region. These fact-filled Quick Reference Sheets bbcmsn you to get all-important information at a glance, helping you to focus your study on areas of weakness and to enhance memory retention of essential exam concepts.
Jay has also worked in IT in the higher education and service provider fields. Prior to this position, he was a Cisco instructor and course director for Global Knowledge.
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Other Things You Might Like. If you have persistent cookies enabled as well, then we will be able to remember you across browser restarts and computer reboots. Register your product to gain access to bonus material or receive a coupon. One of the consequences of this directed-graph approach is that the algorithm has no way to handle a multiaccess network, such as an Ethernet VLAN. On a point-topoint link, no DR is elected and all traffic is multicast to RFC-compliant mode that uses DRs and requires manual neighbor configuration. Resilient RFC compliant mode that automatically discovers neighbors.
All other routers on that link become adjacent only to the DR and BDR, not to each other they stop at the two-way state. The DR is responsible for creating and flooding a network LSA type 2 advertising the multiaccess link. The DRs use IP address Requires manual neighbor configuration.
Step 1. If none are heard within the dead time, it declares itself the DR. Uses DRs and automatic neighbor discovery. Proprietary when used on WAN interface. A priority of zero removes a router from the election. If the default interface type is unsatisfactory, you can statically configure it with the command ip ospf network under interface configuration mode: Router config-if ip ospf network point-to-multipoint When using the NBMA or P2MP nonbroadcast mode, neighbors must be manually defined under the routing process: Router config-router neighbor Because of this, the DR is sometimes the first device that comes online with a nonzero priority.
The default priority is one. Priority can be set with the ip ospf priority command in interface configuration mode. Router config-if ip ospf priority 2 Nonbroadcast Multiaccess NBMA Networks Routing protocols assume that multiaccess links support broadcast and have full-mesh connectivity from any device to any device. If there is a subset of the topology with full connectivity, then that subset can use a multipoint subinterface.
This section discusses route summarization, default routes, stub areas, and virtual links. Summarization prevents topology changes from being passed outside an area and thus saves routers in other areas from having to run the SPF algorithm. Summarization decreases the number of routes exchanged, and thus the size of the databases. The following command advertises The following example summarizes a range of external routes to Router config-router summary-address This provides the ultimate benefit of summarization by reducing routing information to a minimum.
This command, without the keyword always, readvertises a default route learned from another source into OSPF. If the always keyword is present, OSPF advertises a default even if one does not already exist in the routing table. The metric keyword sets the starting metric for this route. Router config-router default-information originate [always] [metric metric] Alternatively, a default summary route can also be produced using the summary-address command or the area range command.
These commands cause the router to advertise a default route pointing to itself.
Reducing routing information in non-backbone areas is a common requirement because these routers are typically the most vulnerable in terms of processor and speed, and the links that connect them usually have the least bandwidth. A specific concern is that an area will be overwhelmed by external routing information. Stub and Not-So-Stubby Areas Another way to reduce the route information advertised is to make an area a stub area.
Configuring an area as a stub area forces its ABR to drop all external type 5 routes and replaces them with a default route. To limit routing information even more, an area can be made totally stubby using the no-summary keyword on the ABR only. In that case, all interarea and external routes are dropped by the ABR and replaced by a default route. The default route starts with a cost of 1; to change it, use the area default-cost command. The example that follows shows area 2 configured as a totally stubby area, and the default route injected with a cost of 5: Router config-router area 2 stub no-summary Router config-router area 2 default-cost 5 Stub areas are attractive because of their low overhead.
External routes are advertised as type 7 routes by the ASBR. The ABR converts them to type 5 external routes when it advertises them into adjacent areas. Configure each end of a virtual link on the ABRs of the transit area with the command area area-number virtual-link router-id. Each end of the link is identified by its RID. The area listed in the command is the transit area, not the area being joined by the link. The configuration for R1 is: R1 config router ospf 1 R1 config-router area 1 virtual-link When this is not possible, you can use a virtual link to bridge across an intermediate area.
Figure shows a virtual link connecting two portions of area 0. R2 config-router area 1 virtual-link Additionally, virtual interfaces are treated as actual interfaces by the OSPF process, and thus, their status can be verified with the show ip ospf interface interface-id command. By default, the router does no authentication.
Note that the commands are slightly different. The optional keyword message-digest is required in two of the commands, and a key number must be specified. Note that authentication commands are necessary both under the OSPF process and the interface configuration. All OSPF neighbors reachable through an interface configured for authentication must use the same password.
You can, however, use different passwords for different interfaces. IS-IS is a classless interior gateway protocol that uses router resources efficiently and scales to large networks, such as large Internet service providers ISP. Table lists some IS-IS terms, acronyms, and their meanings. End System ES A host, such as a computer. Seperate level 1 and level 2 IIHs exist. The last byte of a NET is always zero. Addresses are assigned per device, not per interface as with IP. Identifies the process on the device, such as routing. The sequence number helps a router maintain the most recent link state information.
Donohue: CCNP Routing and Switching v2.0 Exam Practice
Figure shows an IS-IS network divided into areas. R3, R6, and R4 are the backbone in Figure Routes to networks only within the local area intra-area routing. Uses a default route to the nearest Level 2 router for traffic bound outside the area. Keeps one LSDB for the local area. When routing, compares the area of the destination to its area. If they are the same, routes based on system ID. If not, sends traffic to Level router. Area Routes to networks in other areas interarea routing.
The routing is based on area ID.