Routing and Routing Protocols PJC CCNA Semester 2 Ver. 3.0 by William Kelly

Routing Basics Routing is the process of forwarding packets from a source to a destination based on the destination IP address of the packet Routing occurs at layer 3 of the OSI model (network layer) Routes can be entered by the administrator (static) or learned from other routers (dynamic) The network layer provides a “best-effort” delivery system The router uses a routing table to send packets from a source to a destination

How Routers Route Packets Consistent end-to-end Network addressing is the key to routing Broadcasts are minimized and bandwidth is conserved

The 2 Functions of a Router Best Path Determination – The router determines the best path to a destination by examining the Network portion of an address and consulting it’s routing tables (a map of the network contained in each router) Switching – A router accepts a packet on one interface and forwards it to another interface

Routed vs. Routing Protocols Routed protocols are network protocols that provide enough information for a packet to be forwarded from one host to another Routing protocols allow routers to communicate information about network paths and to maintain tables

Routed vs. Routing Protocols Routed protocols are network protocols that provide enough information for a packet to be forwarded from one host to another Routed protocols allow routers to communicate information about network paths and to maintain tables

Common Routed and Routing Protocols Routed Protocols  IP  IPX  Appletalk Routing Protocols  RIP  IGRP  OSPF  EIGRP  BGP

Static Routing Routing instructions manually entered by an administrator Routes must be changed manually when the network topology changes Static routing is labor intensive Static routes are used to enhance security and to set up routes accessible by only one path

Network Layer Protocols

Configuring a Static Route Syntax for entering a static route using the interface: Router(config)# ip route S1 Syntax for entering a static route using the next hop address: Router(config)# ip route Syntax for entering a default route (sometimes called a quad route): Router(config)# ip route S1 Syntax for entering a quad route with an administrative distance Router(config)# ip route

Syntax for entering a static route using the interface: Router(config)# ip route Examining Static Route Syntax Syntax for entering a static route using the interface: Router(config)# ip route S1 destination network address next hop interface next hop address destination network address

Common Administrative Distances

Application of Administrative distances in Static Routes When using a next hop address the default administrative distance is 1 When using an outgoing interface the default administrative distance is 0

Dynamic Routing Dynamic routing allows routers to automatically share routing (topology) information with other routers

Routing Protocols RIP – distance vector protocol, metric is hop count, max hop count is 15, updates every 30 seconds IGRP – distance vector protocol, metric is bandwidth, delay, load, and reliability, highly scalable for large networks, updates every 90 seconds OSPF – link state protocol, uses triggered updates, VLSM compliant EIGRP – Cisco proprietary hybrid protocol, VLSM compliant BGP – exterior routing protocol that was designed to work between ISP’s

Commonly Used Metrics Bandwidth – data capacity of a link Delay – length of time for a packet to travel through links Load – amount of network activity Reliability – error rate Hop Count – number of routers a packet must traverse Ticks – each tick is 1/18 of a second Cost

Link State Basics Link State Protocols use the Link State Algorithm (also called the Dijkstras algorithm) 1.Link State Advertisements (LSA’s) are transferred between routers to provide topology information 2.Each router maintains a topology database of LSA information 3.The Dijkstras algorithm computes the shortest paths to different networks 4.The routing table is then populated with the best paths

Link State Concerns Processor Overhead Memory requirements Bandwidth consumption – The initial discovery process is bandwidth intensive; thereafter, minimal bandwidth is required

Hybrid Routing Protocols Similar to distance vector protocols in that metrics are used but the metrics are more accurate. Similar to Link State protocols in that triggered updates are used instead of period updates Examples are IS-IS and EIGRP

Configuring a Router to Use Routing Protocols Starting routing Router(config)# router protocol {options} ex: Router(config)# router rip Entering Networks Router(config)# network network-number ex: Router(config)# network Note: A separate network line must be used to enter every network whose interface will participate in the sending and receiving of routing updates

Autonomous Systems Interior Gateway Protocols (IGP) were designed to be used in a network designed to be administered by a single organization Exterior Gateway Protocols (EGP) were designed to be used between networks that are controlled by two organizations. EGP’s such as BGP are used between ISP’s Every autonomous system is assigned a 16 bit identifying number by the American Registry of Internet Numbers (ARIN)