OSPF.

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Presentation transcript:

OSPF

OSPF Topics OSPF features OSPF areas OSPF operation OSPF on multi-access broadcast networks OSPF LSAs OSPF metric OSPF load balancing OSPF configuration OSPF authentication

OSPF Features Fast convergence Granular metric Supports VLSM Hierarchical design/route summarization Uses multicasts Supports authentication

OSPF Overview Link State Routing Protocol Router advertises the state of it’s links (connections to networks) Forms neighbor relationships (adjacencies) before exchanging routing information Neighbor information maintained in neighbor table Advertisements flooded within area

OSPF Areas Areas restrict certain advertisements so that in a large environment not all advertisements flooded everywhere Every AS should have an area 0 - Backbone All other areas connect to Backbone Summarization can be configured at area borders – further reduces advertisements Router with interfaces in two or more areas is Area Border Router (ABR)

OSPF Operation First forms adjacencies Floods LSAs requires that certain criteria be met Floods LSAs sent to 224.0.0.5 collected in LSA database Calculates shortest routes - Dykstra Maintains adjacencies with hellos Sends updates only when changes occur

OSPF Operation Multi-access network Designated Router first determined First router active becomes DR Second router active becomes BDR All others become ODR If DR goes down, BDR becomes DR and new BDR elected Router with highest priority wins. If tied, Router with highest OSPF Router ID

OSPF Priority and RID OSPF priority set on per-interface basis default priority is 1 command is “ip ospf priority <number>” priority of 0 means can’t become DR OSPF Router ID – set 3 possible ways Router ID command. If not set then - Highest loopback address. If not set then – Highest active IP address

OSPF LSAs LSA Type 1 – LSA Type 2 – LSA Type 3 – sent by every router advertises it’s OSPF interfaces LSA Type 2 – sent by DR contains a list of all routers on subnet LSA Type 3 – sent by ABR into other areas advertises area networks and metrics

OSPF Metric 10 to the 8th/Bandwidth Referred to as cost 19.2 kbps Source Destination Purpose: This figure presents the IGRP metric with its five possible components. Emphasize : Bandwidth and delay are the two metrics that are most commonly used. They also comprise the default metric. Note: Changing IGRP metrics can have great impact on network performance. Describe the IGRP 24-bit metric field: Bandwidth—Minimum bandwidth on the route in kilobits per second. Delay—Route delay in tens of microseconds. Reliability—Likelihood of successful packet transmission expressed as an integer from 0 to 255. Loading—Effective bandwidth of path. MTU—Minimum MTU in path, expressed in bytes. The following equation calculates the metric. It is presented for instructors and is not required to be taught. metric = [k1 * bandwidth + (k2 * bandwidth) / (256 - load) + k3 * delay] If k5 does not equal 0, an additional operation is done: metric = metric * (k5/(reliability + k4)) The default constant values are k1=k3=1 and k2=k4=k5=0. Again, if default values are set, metric = bandwidth + delay. The constants (k1, k2, k3) can be changed using the metric weights command. Changes to the IGRP constant values should be made with great care. 10 to the 8th/Bandwidth Referred to as cost

OSPF Load Balancing Maximum six equal paths – default 4 equal paths New Route Source Initial Route Purpose: The figure presents how IGRP load sharing improves throughput and increases reliability. Emphasize: Only feasible paths can be used for IGRP load sharing. Load-balancing methods vary according to the switching mode because the data structures for process switching, fast switching, and autonomous switching are all different. When process switching, the processor load balances packet by packet. When fast, autonomous, or silicon switching, load balancing is done destination by destination. By default, the amount of variance is set to one, which results in equal-cost load balancing. You can use the default-metric command to change the default metric. Transition: The following pages describe how to configure the IGRP routing protocol. Destination Maximum six equal paths – default 4 equal paths

Configuring OSPF Router(config)#router ospf process-id Defines OSPF as the IP routing protocol Purpose: This figure explains how to use the router igrp and network commands to configure an IGRP process. Emphasize: Note that the AS keyword is required for IGRP. You can use multiple network commands to specify all networks that are to participate in the IGRP process. Only those networks specified will be published to other routers. network network-number wild-card-mask area-id Selects participating attached networks

OSPF Configuration Example 172.16.1.0 192.168.1.0 A C 172.16.1.1 10.1.1.1 10.1.1.2 192.168.1.1 router ospf 50 network 172.16.1.1 0.0.0.0 area 0 network 10.1.1.0 0.0.0.255 area 0 Purpose: The figure shows how the IGRP commands operate on the example network. Emphasize: An administrator only specifies directly connected networks that he wishes to publish to other routers. Without the network command, nothing is advertised. With a network command, the router will advertise every subnet within the Class A, B, or C network specified in the configuration. router ospf 75 network 192.168.1.0 0.0.0.255 area 0 network 10.0.0.0 0.255.255.255.0 area 0

Verifying the Routing Protocol—OSPF 172.16.1.0 192.168.1.0 A B C 172.16.1.1 10.1.1.1 10.1.1.2 10.2.2.2 10.2.2.3 192.168.1.1 Routing Protocol is "ospf 1" Outgoing update filter list for all interfaces is not set Incoming update filter list for all interfaces is not set Router ID 172.16.1.1 Number of areas in this router is 1. 1 normal 0 stub 0 nssa Maximum path: 4 Routing for Networks: 10.1.1.1 0.0.0.0 area 0 172.16.0.0 0.0.255.255 area 0 Routing Information Sources: Gateway Distance Last Update Distance: (default is 110) Purpose: This figure shows how the show ip protocol command is used to monitor IGRP operation. Emphasize: The command displays the routing protocols that are active on the router for IP. It also gives network and timer information. In this example, IGRP is displayed. Point out the timing information. Point out the list of networks for which the router is injecting routes. Point out the administrative distance metric.

OSPF Show Commands show ip route ospf show ip ospf interfaces show ip ospf neighbors show ip ospf database