7.7 Configuring OSPF

7.6 Open Shortest Path First (OSPF) Basics

• OSPF is an open standard routing protocol
• OSPF works by using the Dijkstra algorithm
• OSPF features:

1. Consists of areas and autonomous systems
2. Minimizes routing update traffic
3. Allow scalability
4. Support VLSM/CIDR
5. Has unlimited hop count
6. Allow multi-vendor deployment (open standard)

7.5 Verifying EIGRP

• EIGRP troubleshooting commands:

7.4 Load Balancing with EIGRP

7.3 Configuring EIGRP

• EIGRP can be configured through two modes:

1. Router Config Mode
2. Interface Config Mode

• Router config mode enables the protocol, determines which networks will run EIGRP, and sets global characteristics
• Interface config mode allows customization of summaries, metrics, timers and bandwidth

7.2 Using EIGRP to support large networks

EIGRP features:

• Support for multiple ASes on a single router
• Support for VLSM and summarization
• Route discovery and maintenance

7.1 EIGRP Features and Operation

• EIGRP includes the subnet mask in its route updates
• EIGRP is hybrid routing protocol (has characteristics of both distance-vector & link-state protocols)
• EIGRP sends distance-vector updates containing info about networks plus cost of reaching them from the perspective of advertising router and synchronizes routing tables between neighbors at startup and then send specific updates only when topology changes occur
• EIGRP has a max hop count of 255 ( default = 100)
• EIGRP main features:

• EIGRP supports different network layer protocols (IP, IPX, AppleTalk & IPv6) through the use of PDM (protocol-dependent module)
• Each EIGRP PDM will maintain a separate series of tables containing the routing info that applied to a specific protocol
• EIGRP neighbor-ship establishment conditions: (Hello or ACK received; AS numbers match; Identical metrics (K values))
• Feasible distance: Best metric along all paths to a remote network, including the metric to the neighbour that is advertising that remote network
• Reported/advertised distance: Metric of a remote network, as reported by a neighbor
• Neighbor table: Each router keeps state info about adjacent neighbors
• Topology table: populated by PDM and acted upon by Diffusing Update Algorithm (DUAL)
• Feasible successor: path whose reported distance is less than the feasible route, and it's considered a backup route
• Succesor: best route to a remote network
• EIGRP uses a proprietary protocol called Reliable Transport Protocol (RTP) to manage the communication of message between EIGRP-speaking routers
• EIGRP uses Diffusing Update Algorithm (DUAL) for selecting and maintaining the best path to each remote network
• DUAL features:

7.0 Enhanced IGRP (EIGRP) & Open Shortest Path First (OSPF)

• EIGRP is proprietary Cisco protocol
• OSPF is another popular routing protocol

6.8 Verifying Your Configurations

Following commands are used to verify routed and routing protocols:

• show ip route
• show ip protocols
• debug ip rip

6.7 Interior Gateway Routing Protocol (IGRP)

• IGRP is a Cisco-proprietary distance-vector routing protocol (all routers in network must be Cisco)
• Main difference btw IGRP & RIP : During IGRP configuration, autonomous system number is used (all router must use same number to share routing info)
• IGRP vs RIP :

6.6 Routing Information Protocol (RIP)

• RIP version 1 uses only classful routing - all devices in the network must use the same subnet mask
• RIP version 2 uses classless/prefix routing - send subnet mask information with route updates
• RIP uses four different kinds of timers - Route update timer (30s), Route invalid timer (180s), Holddown timer (180s), Route flush timer (240s)
• RIP v1 vs. RIP v2:

• RIPv2 is classless and works in VLSM and dis-contiguous networks

CCNA 6.5 Distance-Vector Routing Protocols

• DVR protocol passes complete routing table contents to neighboring routers, which then combined the received routing entries with their own routing tables to complete the router's routing table
• Pinhole congestion (RIP) :

• Initial routing table with DVR (IP, Exit Interface, Hop Count):

• DVR - slow convergence time
• Converged routing tables:

• DVR keeps track of changes to internetwork by broadcasting periodic routing updates out all active interface
• Routing loops (counting to infinity) occur when every router isn't updated simultaneously
• Maximum hop - RIP up to 15 (solve routing loops)
• Splilt horizon enforce the rule that routing info cannot be sent back in the direction from which it was received (solve routing loops)
• Route poisoning assigns down network with hop counts of 16 or unreachable/infinite (solve routing loops)
• A holddown prevents regular update messages from reinstating a route that is going up and down (flapping)

CCNA 6.4 Dynamic Routing

• Dynamic routing is when protocols are used to find networks and update routing tables on routers
• Two types of routing protocols are used in internetwork: interior gateway protocols (IGPs) and exterior gateway protocols (EGPs)
• IGPs are used to exchange routing info with routers in the same autonomous system (AS)
• An AS is a collection of networks under the same administrative domain (all routers sharing the same routing table info)
• EGPs are used to communicate between ASes. ( ie. Border Gateway Protocol - BGP)
• Administrative distance (AD) is used to rate the trustworthiness of routing info received on a router from a neighbour router
• AD is an integer from 0 - 255 with 0 is the most trusted and 255 means no traffic will be passed via this route
• AD, routing protocol metrics ( hop count, bandwidth) are used to determine best path to remote network:

• There are three classes of routing protocols: Distance vector, Link state & Hybrid
• Distance-vector protocols find the best path to a remote network by judging distance - #s of hop. (ex. RIP, IGRP)
• Link-state protocols (Shortest-path-first protocol) create three separate tables: one keeps track of directly attached neighbors, one determines the topology of entire internetwork, one used as routing table. (ex. OSPF)
• Hybrid protocols used both distance-vector and link-state protocols. (ex. EIGRP)