6: Routing Working at a Small to Medium Business

Basics Routers can be used to break network smaller –Subnet To go from router to router –Routing table –Finds route to other networks –Statically set –Dynamically learned

The Routing Table Router looks at destination IP & SM –ANDing the destination IP & SM Result is a network # Looks in table for the match & forwards it out that interface No match= default route, if set Routing Table has list of networks & paths

The Routing Table

Configuring the Static Route ip route destination_network subnet_mask next hop ip or outgoing int R1(config) #ip route What would be the static route on R2 to reach the ladies’ network? PT

Dynamic Routing Protocols Maintain tables when changes occur –Bad cables, interfaces go down, better route learned –Best route to a network in table –Removes routes when no longer valid When all routers agree on topology= converged Two routers can exchange these tables as long as they use the same protocol

Distance Vector Routing Passes updates every so often to connected neighbors Distance & Direction –Metric (hops, speed, reliability, etc)

Distance Vector Routing & Lab Interface that leads to the connected network has a distance (metric) of 0 Neighbors update each other & add on how far away it is Star is 0 away Star is 1 away Star is 2 away

Practice Lab

RIP- Routing Information Protocol DV Metric is Hops –Only15 Max; 16 is unreachable (D) Updates every 30 seconds by default –Sends entire routing table (D) –If change, update sent immediately (triggered) –Slow to converge whole network (D) Administrative Distance is 120

RIP RIPv1 –Doesn’t send subnet mask in updates –Classfull subnetting RIPv2 –Classless subnetting

RIP

EIGRP Enhanced Interior Gateway Routing Protocol –Cisco proprietary DV (mix LS & DV) –AD of 90 –Many metrics (bandwidth, delay, load, reliability) –Up to 224 hops –Routing Table, Neighbor Table, Topology Table –Updates on start of router & only when a change happens –VLSM Support

EIGRP Tables Neighbor Table –Has info about neighbor direct connect routers Topology Table –Built from advertisements of its neighbors –Contains ALL routes advertised by neighbor routers –DUAL calculates the shortest path to a destination and installs it into the routing table –Is able to find the best alternate path quickly when a network change occurs –If no alternate route exists it asks its neighbors to find a new path to the destination

Link State Routing Knows routes further away LSA Topological database –Info from LSAs SPF –Each change causes new calc & database update –Map of network from point of view of the router –Info in tree is used to build the routing table

OSPF AD of 110 Metric is cost Uses SPF Sends updates only when the topology changes –Does not send periodic updates of the entire routing table Fast convergence Supports VLSM Provides route authentication

Which to Use??????

DV vs. Link State

Summary of Routing Protocols ProtocolDV or LSADMetricFeatures RIP v1DV120Hops 15 hops max RIP v2DV120Hops 15 max; VLSM EIGRP DV- Hybrid 90 Bandwidth, Load, Delay, Reliability Cisco’s; VLSM OSPFLS110Cost Multi- vendor; VLSM

Routing May be multiple routes to same path –Use AD (metrics) to pick best path –Lowest AD is best

Configure RIP Router(config)#router rip Router (config-router)#version 2 Router(config-router)#network network-number

Verifying RIP Ping Show ip route Show ip protocols PT Lab

Show ip protocols output

Show ip route output Administrative Distance/metric; lower AD to a network=more trustworthy route

Problems with RIP

Autonomous Systems A network under one administration –An ISP & its customers Large businesses have their own AS –Each has unique AS# –Manages all routes to it

Activity

Routing Between AS IGP runs within your network & between your routers –RIP, EIGRP, OSPF EGP runs between different AS –Most common is BGP –Runs on border gateway routers The router at the end of an AS –Finds the best path between AS

AS- LinkLink

Routing Across Internet

Help from the ISP Keep the Internet connection available ISP provides backup routes & routers ISP advertises routes to other AS –If route fails, sends an update with a backup route

ISP Handling of Traffic- LinkLink Local traffic –Stays within the AS Transit traffic –Outside of AS to go in/through AS –Like detouring traffic from Rt.55 onto Tanyard Rd. Could cause overflow of traffic Can’t handle that much AS may or may not allow this traffic

Configure the Border Gateway Static Route to ISP If router participates in the AS, configure BGP Lab on PT

Review

6: Routing Working at a Small to Medium Business