CCNA

  The following table lists the differences between the three most popular interior routing protocols:   Feature RIP EIGRP OSPF Type distance vector hybrid distance vector Metric hop count bandwidth and delay cost Speed of convergence slow fast fast Routing classful (RIPv1), classless(RIPv2) classless classless Updates periodical broadcast (RIPv1), multicast(RIPv2) multicast multicast Manual summarization no (RIPv1), yes (RIPv2) yes yes Supported on non-Cisco routers yes no yes Configuration complexity easy medium hard

  The following table lists the differences between OSPF and EIGRP:

  Here is a list of the most important OSPF features: link state routing protocol classless routing protocol supports VLSM (Variable Length Subnet Mask) converges fast uses the concept of areas uses multicast address for routing updates (224.0.0.5 and 224.0.0.6) sends partial routing updates supports only equal cost load balancing manual summarization can be done only on ABRs and ASBRs uses interface cost as a metric uses SPF algorithm to calculate the best paths open standard each router inside an area has the same topology table supports clear-text and MD5 authentication

  Route summarization helps reduce OSPF traffic and route computation. OSPF, unlike EIGRP, doesn’t support automatic summarization. Also, unlike EIGRP, where you can summarize routes on every router in an EIGRP network, OSFP can summarize routes only on ABRs and ASBRs. The following command is used for OSPF summarization: (config-router) area AREA_ID range IP_ADDRESS MASK To better understand OSPF summarization, consider the following example network: All three routers are running OSPF and exchanging routers. Before OSPF summarization is configured, the router R1 inside the backbone area has two entries for the networks 11.0.0.0/24 and 11.0.1.0/24 in its routing table. We could summarize these two subnets on R2, so that R1 receive only one routing update for both subnets. To do that, the following command can be used on R2: Now, R1 has only one entry in its routing table for R3’s directly connected subnets: NOTE Be careful with summarization. In this case, router R1 thinks that R2 ...

  OSPF can be configured to authenticate every OSPF message. This is usually done to prevent a rogue router from injecting false routing information and therefore causing a Denial-of-Service attack. Two types of authentication can be used: 1.     clear text authentication  – clear text passwords are used 2.     MD5 authentication  – MD5 authentication is used. This type of authentication is more secure because the password doesn’t go in clear-text over the network. NOTE With OSPF authentication turned on, routers must pass the authentication process before becoming OSPF neighbors.   To configure clear text authentication, the following steps are required: configure the OSPF password on the interface by using the  ip ospf authentication-key PASSWORD  interface command configure the interface to use OSPF clear-text authentication by using the  ip ospf authentication  interface command   In the following e...

  Based on the network type, OSPF router can elect one router to be a  Designated Ruter (DR)   and one router to be a   Backup Designated Router (BDR) . For example, on multiaccess broadcast networks (such as LANs) routers defaults to elect a DR and BDR. DR and BDR serve as the central point for exchanging OSPF routing information. Each non-DR or non-BDR router will exchange routing information only with the DR and BDR, instead of exchanging updates with every router on the network segment. DR will then distribute topology information to every other router inside the same area, which greatly reduces OSPF traffic. To send routing information to a DR or BDR the multicast address of 224.0.0.6 is used. DR sends routing updates to the multicast address of 224.0.0.5. If DR fails, BDR takes over its role of redistributing routing information. Every router on a network segment will establish a full neighbor relationship with the DR and BDR. Non-DR and non-BDR routers will es...