Path Determination Static Routes Dynamic Routing Protocols Routing Information Protocol (RIP) Interior Gateway Routing Protocol (IGRP) Open Shortest Path First (OSPF) Enhanced Interior Gateway Routing Protocol (EIGRP) Border Gateway Protocol (BGP)

Routing Overview In order to travel from one network to another, some device must know to transport that information Routing is the process by which information gets routed from one location to another: mail telephone calls trains

Router Information A router (or entity performing routing) needs to know: Destination Address – What is the destination address of the item to be routed? Information Sources – From which source (i.e., other routers) can the router learn paths to a given destination Possible Routes – What are the initial possible routes or paths to the intended destination Best Routes – What is the best path to the intended destination Routing Information Maintenance and Verification – A way to verify that known paths to destinations are current and valid

Connected Routes 10.120.2.0 E0 172.16.0.0 S0 Network Protocol Destination Network Exit Interface Connected Learned 10.120.2.0 172.16.0.0 E0 S0

Table Construction If destination is directly connected, router knows which port to use when forwarding packets If destination networks are not directly attached, router must learn best route Manually by network administrator Dynamically by collecting information about processes running through the network

Forwarding Packets Static Routes – Routes learned by router when administrator manually establishes route. The administrator must update these routes when topology changes occur Dynamic Routes – Routes automatically learned by router after administrator configures a routing protocol that helps determine routes. Route knowledge is automatically updated whenever topology changes

Enabling Static Routes Static routes are administratively defined routes that specify the explicit path packets must take to destination They are administratively defined and allow very precise control over routing behavior Important if Cisco IOS software cannot build a route to destination Gateway of “last resort” – address a router would send a packet destined for a network not listed in the routing table

Stub Network Static routes are commonly used when routing from a network to a stub network Stub network (aka “leaf node”) is a network accessed by a single route Stub Network 172.16.2.2 Network S0 172.16.1.0 172.16.2.1

End-to-End Connectivity Static route is configured for connectivity to data link, not directly to router End-to-end connectivity is configured in both directions

Configuring Static Routes Enter ip route in global configuration mode. Parameters for ip route further define the static route Static route allows manual configuration of routing table Entry will remain in routing table as long as path is active Only exception is permanent option – route will remain in table even if path is not active

Static Route To Stub Static route from Router A to stub network is configured as follows: RouterA(config)#ip route 172.16.1.0 255.255.255.0 172.16.2.1 ip route – Identifies static route command 172.16.1.0 – Specifies static route to destination subnetwork 255.255.255.0 – Indicates subnet mask 172.16.2.1 – Specifies IP address of next-hop router in path to destination Stub Network A B 172.16.2.2 Network S0 172.16.1.0 172.16.2.1

Default Route Default route is special type of static route for situations in which the route from source to destination is not known, or it is infeasible for the routing table to store sufficient information about all possible routes Default route is “gateway of last resort”

Static Route From Stub To configure default route, you would enter following at router B: RouterB(config)#ip route 0.0.0.0 0.0.0.0 172.16.2.2 ip route – Identifies static route command 0.0.0.0 – routes to non-existent subnet (with special mask, it denotes the default network) 0.0.0.0 – Specifies special mask indicating default route 172.16.2.2 – Specifies IP address of next-hop router to be used as default for packet forwarding Stub Network A B 172.16.2.2 Network S0 172.16.1.0 172.16.2.1

Learning Routes Static routes are useful in some situations It is not satisfactory that the network administrator reconfigure routers to accommodate change Another method is to learn available routes automatically accommodating changes

Routing Protocols S0 10.120.2.0 E0 172.16.1.0 S1 172.17.3.0 Network Protocol Destination Network Exit Interface Connected RIP IGRP 10.120.2.0 172.16.1.0 172.17.3.0 E0 S0 S1

Routing Protocols Dynamic routing relies on a routing protocol to dissiminate and gather knowledge Routing protocol defines set of rules used to communicate with neighboring routers Routing protocol is a network layer protocol that intercepts packets from other routers to learn and maintain a routing table

Routing Protocols (Cont) Routing protocols describe the following information How updates are conveyed What knowledge is conveyed When to convey knowledge How to locate recipients of updates Examples of routing protocols are: RIP IGRP

Routed Protocols Routed protocols such as TCP/IP and IPX define the format and use fields within a packet to provide a transport mechanism for user traffic As soon as routing protocol determines a valid path between routers, the router can route a routed protocol

Types of Routing Protocols Interior Gateway protocols (IGP) – Used to exchange routing information within an autonomous system. Examples: RIP IGRP Exterior Gateway Protocols (EGP) – Used to exchange routing information between autonomous systems. Example: BGP EGPs are not discussed in this book

IGP Vs EGP IGP: RIP, IGRP EGP: BGP Autonomous System 100

Autonomous System Collection of networks under a common administrative domain Internet Assigned Numbers Authority (IANA) allocates autonomous system numbers Using IANA-assigned autonomous system number is necessary only if organization plans to use EGP public network such as the internet

Administrative Distance Multiple routing protocols and static routes may be used at the same time If several routing sources provide common routing information, an administrative distance value is used to rate trustworthiness of each routing source Allows Cisco IOS software to discriminate between sources of routing information For each network learned, IOS selects route from routing source with lowest administrative distance It is a number between 0 and 255. Routing protocol with lowest administrative distance has most likelihood of being used

Administrative Distance (Cont) Send packet from router A to network E by best route IGRP Administrative Distance = 100 Router A Router B RIP Administrative Distance = 120 E Router C Router D

Default Values Route Source Default Distance Connected interface Static route address 1 EIGRP 90 IGRP 100 OSPF 110 RIP 120 External EIGRP 170 Unknown/Unbelievable 255 (Will not be used to pass traffic)

Non-Default Values Non-default values may be necessary when redistributing routes Network administrator can use Cisco IOS to configure administrative distance values on a per-router, per-route basis See ACRC coursebook available from CISCO press

Classes of Routing Protocols Distance Vector – Determines direction (vector) and distance of any link in the internetwork. Examples include RIP and IGRP Link-state – (also called shortest path first) recreates exact topology of entire internetwork for route computation (or at least component where router is located). Examples include OSPF and NLSP Balanced Hybrid – Combines aspects of link-state and distance vector algorithms. Example is EIGRP

Comparison There is no single best routing algorithm for all internetworks All routing protocols provide information differently

Distance Vector Protocols Also known as Bellman-Ford-Fullerton algorithms Pass periodic copies of routing table from router to router and accumulate distance vectors Distance means how far Vector means which direction Regular updates between routers communicate topology changes Each router receives routing table from its direct neighbor

Table Updates B A C D C B A Routing Table Routing Table Routing Table

Algorithm Activities Identify sources of information Discover routes Select best route Maintain routing information

Information Exchange 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S1 B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 2 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 1 10.1.0.0 10.3.0.0 S0 10.4.0.0 E0 10.2.0.0 1 10.1.0.0 2

Multiple Paths There might be multiple paths to any given destination network When table is updated, primary objective is to determine best path Each distance vector routing protocol uses a different routing algorithm to determine best route Algorithms generate a number called metric value for each path through the network Smaller the metric, the better the path

Metrics Hop count – Number of routers through which packet will pass Ticks – Delay on a data link using IBM PC clock ticks ( 55 milliseconds) Cost – Arbitrary value, usually based on bandwidth, dollar expense, or another measurement assigned by network administrator Bandwidth – Data capacity of link. 10 Mbps Ethernet is better than 64Kbps leased line Delay – Length of time to move from source to destination Load – Amount of activity on a network resource such as router or link Reliability – Usually refers to bit-error rate of each network link MTU – Maximum transmission unit. Maximum frame length in octets that is acceptable to all links on path

Transmission from A to B 56 IGRP Bandwidth Delay Load Reliability MTU RIP Hop Count T1 56 C T1 IPX Ticks, Hop Count B

Methods IGRP – Bases decision on combined characteristics, such as bandwidth, delay, reliability, and MTU. Emphasis is on bandwidth and delay, so it would choose T1 lines RIP – Hop counts are equal, so it would load balance between paths

Distance Vector Events The following occurs step-by-step from processor to processor Topology change Network discovery process Topology change updates The entire routing table is sent to each adjacent or directly connected neighbor Routing table contains information about total path cost (defined by metric) and logical address of the first router on the path to each network it knows about Updates are compared to own routing table Router adds cost of reaching neighbor to path cost reported by neighbor Finding a better route results in update of routing table

Maintaining Routes Process to update this routing table Process to Topology change causes routing table update Router A sends out updated routing table at the end of next period A B

“Converged” Network 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S1 S0 A B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 2 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 1 10.1.0.0 10.3.0.0 S0 10.4.0.0 E0 10.2.0.0 1 10.1.0.0 2

“Slow” Convergence If network 10.4.0.0 fails, the routing tables should change so that the network slowly re-converges

Start of Counting to Infinity 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X E0 S0 S0 S1 S0 E0 A B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 2 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 1 10.1.0.0 10.3.0.0 S0 10.4.0.0 E0 down 10.2.0.0 1 10.1.0.0 2

Router C Update 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X E0 S0 S0 S1 S0 E0 A B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 2 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 1 10.1.0.0 10.3.0.0 S0 10.4.0.0 2 10.2.0.0 1 10.1.0.0

Router A and B Updates X 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 4 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 3 10.1.0.0 1 10.3.0.0 S0 10.4.0.0 2 10.2.0.0 1 10.1.0.0

Next Iteration X 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S1 S0 E0 B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 6 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 5 10.1.0.0 1 10.3.0.0 S0 10.4.0.0 4 10.2.0.0 1 10.1.0.0 2

Troubleshooting IP distance vector routing algorithms have inherent limits via Time To Live (TTL) value in IP header Router reduces TTL by 1 each time it gets a packet When 0, router discards packet However, routing loop might count to infinity first

Maximum Metric X 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S1 S0 E0 B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 16 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 16 10.1.0.0 1 10.3.0.0 S0 10.4.0.0 16 10.2.0.0 1 10.1.0.0 2

Maximum Metric Setting When value reaches maximum, network is considered unreachable

Split Horizon It is never useful to send information about a route back in the direction from which the original update came

Split Horizon Example Router B has access to network 10.4.0.0 through Router C, so it makes no sense for Router B to announce to Router C that it has access to 10.4.0.0 through Router C Router B announced 10.4.0.0 network to Router A, so it makes no sense for Router A to announce its distance to Router B Having no alternate path to 10.4.0.0, Router B concludes 10.4.0.0 is inaccessible

Split Horizon Routing Tables 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X E0 S0 S0 S1 S0 X E0 X A B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 down 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 down 10.1.0.0 1 10.3.0.0 S0 10.4.0.0 down 10.2.0.0 1 10.1.0.0 2

Route Poisoning Route Poisoning is another form of Split Horizon Attempts to eliminate routing loops caused by inconsistent updates Router sets a table entry that keeps network state consistent while other routers gradually converge Frequently used with “holddown timers (described in next section)

Poisoning Example When 10.4.0.0 goes down, Router C poisons its link to network 10.4.0.0 by entering infinite cost (indicating network is unreachable) By poisoning route to network, Router C is not susceptible to other incorrect updates about 10.4.0.0

Poisoned Route X 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S1 S0 E0 A B C Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 2 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 1 10.1.0.0 10.3.0.0 S0 10.4.0.0 E0 infinity 10.2.0.0 1 10.1.0.0 2

Router B Actions Router B notices that 10.4.0.0 jumps to infinity Router B sends update called poison reverse back to Router C Poison reverse overrides Split Horizon direction Poison reverse serves as acknowledgement that poison message was received

Poison Reverse X 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 E0 S0 S0 S1 S0 E0 A B C Poison Reverse Routing Table Routing Table Routing Table 10.1.0.0 E0 10.2.0.0 S0 10.3.0.0 1 10.4.0.0 2 10.2.0.0 S0 10.3.0.0 S1 10.4.0.0 possibly down 10.1.0.0 1 10.3.0.0 S0 10.4.0.0 E0 infinity 10.2.0.0 1 10.1.0.0 2

Holddown Timers Holddown times are used to prevent regular update messages from inappropriately reinstating a bad route Tell routers to hold any changes that might affect routes for some period of time Holddown period is usually just grater than time necessary to update entire network with a routing change

Holddown Timer Operation Step 1 – When router receives update indicating a network is inaccessible, the router marks the route as inaccessible and starts holddown timer Step 2 – If update arrives from neighboring router with better metric than originally recorded, the router marks the network as accessible and removes holddown timer Step 3 – If a poorer metric update is received from a neighboring router at any time before the holddown timer expires, the update is ignored. Ignoring poorer updates allows more time for knowledge of the change to propagate Step 4 – During holddown period, routes appear in routing table as “possibly down”

Holddown Example X Update after holddown time Network 10.4.0.0 is unreachable 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X E0 S0 S0 S1 S0 E0 A B C Update after holddown time

Triggered Updates If routers wait for regularly scheduled updates, before notifying neighbors of catastrophes, the following serious problems can occur Loops Dropped traffic A triggered update is sent immediately Detecting router immediately sends messages to adjacent routers which in turn notify their neighbors

Triggered Updates X Network 10.4.0.0 is unreachable Network 10.4.0.0 10.1.0.0 10.2.0.0 10.3.0.0 10.4.0.0 X E0 S0 S0 S1 S0 E0 A B C

Triggered Update Problems Packets containing update message can be dropped or corrupted by some link in the network Triggered updates do not occur instantaneously It is possible that a router issue a regular update just before it is about to receive a triggered update, causing a bad route to be reinserted into a neighbor who already received the triggered update Therefore, we couple triggered updates with holddowns

Holddown Timers with Triggered Updates Holddown rule says that when a route is invalid, no new route with the same or worse metric will be accepted at the destination for holddown time Therefore, triggered updates have time to propagate throughout the network

Multiple Solutions X Routers have multiple routes to each other D 10.4.0.0 C X E B A Routers have multiple routes to each other Routers A and D receive triggered update Router B removes its route to network 10.4.0.0

Route Fails X Routers A and D receive triggered update Holddown 10.4.0.0 Holddown C X E B A Holddown Routers A and D receive triggered update Set their own holddown timers Routers A and D in turn send triggered updates to Router E

Route Holddown X Routers A and D send poison reverse to Router B 10.4.0.0 Holddown C X E B Poison Reverse Poison Reverse A Holddown Routers A and D send poison reverse to Router B Router E sends poison reverse to Routers A and D

Holddown Duration Routers A, D and E remain in holddown until one of following occurs: Holddown timer expires New route with better metric is received A flush timer (the time a route is held before being removed) removes the route from the routing table

Packets During Holddown 10.4.0.0 Holddown C X E B Packet for 10.4.0.0 Packet for 10.4.0.0 A Holddown Router E sends message to 10.4.0.0 Router B will drop packet and send ICMP “network unreachable” message

10.4.0.0 Returns to Operation Network 10.4.0.0 returns to operation D C 10.4.0.0 E B Link Up! A Network 10.4.0.0 returns to operation Router B sends a trigger update to Routers A and D notifying them that the link is active After holddown timer expires, Routers A and D add 10.4.0.0 back to their routing table

Network Converges D C 10.4.0.0 E B Link Up! A Routers A and D send Router E a routing update stating that network 10.4.0.0 is up Router E updates its routing table after hoddown timer expires

Link-State and Hybrid Routing Protocols Focus of this chapter has been “distance vector” routing Link-State and Hybrid are alternative routing protocols

Link-State Protocol Diagram TopologicalDatabase SPF Algorithm Link State Packets Routing Table Shortest-Path-First Tree

Link-State Protocol Link-state protocols build routing tables based on a topology database Topology database is built from link-state packets that are passed between all routers to describe the state of a network Database is used by the shortest-path-first algorithm to build the routing table

Shortest-Path Algorithms Link-state algorithms (also known as shortest-path algorithms) maintain a complex database of topology information Distance vector algorithm has non-specific information about distant networks and no knowledge of distant routers Link-state maintains full knowledge of distant routers and how they interconnect Link-state routing uses Link-State Packets (LSPs), a topological database, the SPF algorithm, the resulting SPF tree, and the routing table of paths and ports to each network

Link-State Advantages As networks become larger in scale, link-state becomes more attractive because: Link-state protocols only send updates of a topology change Periodic updates are more infrequent for distance vector protocols Networks running link-state can be segmented into area hierarchies, limiting the scope of route changes Networks running link-state support classless addressing Networks running link-state support summarization

Balanced Hybrid A third protocol, called “Balanced Hybrid,” combines distance vector and link-state protocols Balanced hybrid uses distance vectores with more accurate metrics to determine the best paths to destination networks However, it uses topology changes to trigger routing database updates as opposed to periodic updates Balanced hybrid converges more rapidly, like link-state but emphasizes economy in the use of resources such as bandwidth, memory and processor overhead CISCO’s Enhanced Interior Gateway Routing Protocol is a balanced hybrid protocol

Configuring Dynamic Routing Protocols To enable dynamic routing protocol, perform the following Select a routing protocol, such a RIP or IGRP Select IP networks to be routed Dynamic routing uses broadcasts and multicasts to communicate with other routers When information from other routers is received, it uses routing metric to find the best path to each network or subnet.

Use of IGRP and RIP at Same Router 172.16.0.0 RIP IGRP 160.89.0.0 RIP 172.30.0.0

Router Command The router command starts the routing process router(config)#router protocol [keyword] Protocol is RIP, IGRP, OSPF or EIGRP Keyword refers to an autonomous system in protocols that require an autonomous system such as IGRP

Network Command The network command allows the routing process to determine which interfaces it will participate in the sending and receiving of routing updates The network command starts the routing protocol on all of a router’s interfaces that have IP addresses within the specified network scope The network command also allows router to advertise that network to other routers router(config-router) #network network-number The network-number parameter specifies a directly connected network number For RIP and IGRP, network-number must be based on major-class network numbers, not subnet numbers

Enabled Protocols After the protocol is enabled and a networks path is chosen, the router begins to dynamically learn the networks and paths available in the internetwork

RIP Route Choice 19.2 kbps T1 T1 C T1 The above shows how RIP would choose routes based on hop count

Versions 1 and 2 The book describes RIP version 1 Version 1 is described in RFC 1058 www.isi.edu/in-notes/rfc1058.txt We are using RIP version 2 in our project Version 2 is described in RFCs 1721 and 1722 www.isi.edu/in-notes/rfc1721.txt www.isi.edu/in-notes/rfc1722.txt

General Characteristics of RIP It is a distance vector protocol Hop count is the metric for path selection Maximum allowable hop count is 15 Entire routing table is broadcast every 30 seconds by default Can load balance over as many as six equal-cost paths (four paths is the default)

RIP-1 vs RIP-2 RIP-1 requires that only one network mask can be used per network number for each major classful network being advertised RIP-2 permits variable-length subnet masks (VLSM) on the internetwork Standard RIP-2 supports triggered updates Standard RIP-1 does NOT support triggered updates

RIP Configuration Example router rip network 10.0.0.0 172.16.1.0 192.168.1.0 A B C S2 E0 S3 S2 E0 S3 172.16.1.1 10.1.1.1 10.1.1.2 10.2.2.2 10.2.2.3 192.168.1.1 router rip network 172.16.0.0 network 10.0.0.0 router rip network 192.168.1.0 network 10.0.0.0

Router A router rip selects RIP as the routing protocol network 172.16.0.0 specifies a directly connected network network 10.0.0.0 specifies a directly connected network Router A interfaces connected to networks 172.16.0.0 and 10.0.0.0 will send and receive RIP updates These interfaces will also be advertised to neighboring routers The updates allow the router to learn new topologies

Show IP Protocols Displays values associated with routing timers and network information associated with the entire router

Show IP Protocols RouterA#sh ip protocols Routing Protocol is “rip” Sending updates every 30 seconds, next due in 0 seconds Invalid after 180 seconds, hold down 180, flushed after 240 Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Redistributing: rip default version control: send version 1, receive any version interface Send Recv Key-Chain Ethernet0 1 1 2 Serial 2 1 1 2 Routing for Networks: 10.0.0.0 172.16.0.0 Routing Information Sources; Gateway Distance last Update 10.1.1.2 120 00:00:10 Distance: (Default is 120)

Show IP Protocols Analysis Router A sends updated routing table information every 30 seconds If router running RIP does not receive an update for 180 seconds, marks route as invalid Holddown timer is set to 180 seconds – update to a route that returns to up will not be made for 180 seconds With no update, routing table entry is discarded after 240 seconds It has been 10 seconds since Router A received an update from Router B Advertised routes are listed after Routing for Networks line Administrative distance default is 120

Show IP Route Show ip route displays routing table information The routing table contains entries for all known networks and subnetworks

Show IP Route Example RouterA#sh ip route Codes: C – connected, S – static, I – IGRP, R – RIP, M – mobile, B – BGP D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2 E1 – OSPF external type 1, E2 – OSPF external type 2, E – EGP I – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-2, * - candidate default U – per-user static route, o – ODR T – traffic engineered route Gateway of last resort is not set 172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, Ethernet0 10.0.0.0/24 is subnetted, 2 subnets R 10.2.2.0 [120/1] via 10.1.1.2, 00:00:07, Serial2 C 10.1.1.0 is directly connected Serial 2 R 192.168.1.0/24 [120/2] via 10.1.1.2, 00:00:07, Serial2

Show IP Route Fields Output Description R or C Identifies source of the route – C: directly connected – R: RIP 192.168.1.0 Route’s address of the destination network [120/1] [administrative distance/number of hops] via 10.1.1.2 Address of next hop router to reach the remote network 00:00:07 Time since the route was updated – hours:minutes:seconds Serial2 Interface through which the specified network can be reached

Routing Table Problems If show ip route shows no entries that were learned, routing information is not being exchanged Use show running-config or show ip protocols to check for possible misconfigurations

Debug IP RIP The debug ip rip command displays RIP routing updates as they are sent and received

Debug Router RIP Example RouterA#debug ip rip RIP protocol debugging is on RouterA# 00:06:24: RIP: received v1 update from 10.1.1.2 on Serial2 00:06:24: 10.2.2.0 in 1 hops 00:06:24: 192.168.1.0 in 2 hops 00:06:33: RIP: sending v1 update to 255.255.255.255 via Ethernet0 (172.16.1.1) 00:06:34: network 10.0.0.0, metric 1 00:06:34: network 192.168.1.0, metric 3 00:06:34: RIP: sending v1 update to 255.255.255.255 via Serial2 (10.1.1.1) 00:06:24: network 172.16.0.0 To disable debugging, use no debug ip rip or no debug all

No Debug All no debug all turns off all debugging Debugging output can be overwhelming It is often useful to turn off all debugging

IGRP Interior Gateway Routing Protocol (IGRP) is an advanced distance vector routing protocol developed by Cisco in the mid-1989s

IGRP Features Increased Scalability – Provides improved routing for larger networks as compared with RIP HOP count RIP 15 IGRP default 100 IGRP max 255 Sophisticated Metric Default uses internetwork delay and bandwidth Optionally, reliability, load and MTU can be included Multiple Path Support IGRP can maintain up to 6 unequal cost pats between network source and destination (Unlike RIP) Paths do not mandate equal costs Multiple paths can be used to increase bandwidth or increase route redundancy

IGRP Applicability IGRP should be used in IP networks that require a simple, robust, and more scalable router protocol than RIP IGRP performs triggered updates, which gives it an advantage over RIP-1

IGRP Metrics IGRP’s composite routing metric provides greater accuracy than RIP’s hop-count Path with smallest metric is best By default, IGRP metrics are weighted with constants K1 through K5 Constants convert IGRP metric vector into a scalar quantity

IGRP Metric Components Bandwidth – The lowest bandwidth value in the path Delay – The cumulative interface delay along the path Reliability – Determined by exchange of keepalives Load – Load on a link between source and destination based on bits per second MTU – Maximum Transfer Unit value of the path

IGRP Metric Notes Default Metrics Bandwidth (values between 1200bps and 10gbps) Delay (values between 1 and 2x1023) Reliability and load metrics are unitless and can take values between 0 and 255

IGRP Route Selection Assume two routes are available, one through 19.2kbps lines, and the other through 10mbps lines IGRP will select the routes with 10mbps lines, because it has higher bandwidth

Multiple Paths IGRP supports multiple paths between source and destination Dual equal-bandwidth lines can run a single stream of traffic in a round-robin fashion Switchover is automatic if one line goes down

Unequal Paths Multiple paths can be used even if metrics for the paths are different If metric for one path is three times better than for another path, it will be used three times more often Only routes with metrics in a certain range are used as multiple paths

Unequal-Cost Load Balancing Allows traffic to be distributed among up to six unequal paths to provide greater overall throughput and reliability Following rules apply IGRP will accept up to six paths for a given destination (four by default) Next-hop router in any of the paths must be closer to the destination than the local router is by its best path Alternative path metric must be within specified variance metric

Configuration Commands router(config-router)#router igrp autonomous system router(config-router)#network network-number

IGRP Configuration Example Autonomous System = 100 172.16.1.0 192.168.1.0 A B C S2 E0 S3 S2 E0 S3 172.16.1.1 10.1.1.1 10.1.1.2 10.2.2.2 10.2.2.3 192.168.1.1 router igrp 100 network 172.16.0.0 network 10.0.0.0 router igrp 100 network 192.168.1.0 network 10.0.0.0 router igrp 100 network 10.0.0.0

RouterA Analysis router IGRP 100 – enables IGRP routing process for autonomous system 100 network 172.16.0.0 – associates network 172.16.0.0 and its interfaces with IGRP routing process network 10.0.0.0 – associates network 10.0.0.0 and its interfaces with IGRP routing process

IGRP Updates IGRP sends updates out interfaces in networks 10.0.0.0 and 172.16.0.0 It also advertises directly connected networks 10.0.0.0 and 172.16.0.0, as well as other networks it learns about through IGRP (198.168.1.0)

IGRP Load Balancing The variance router configuration command controls IGRP load balancing router(config-router)#variance multiplier Multiplier parameter specifies the range of metric values acceptable for load balancing Range is from lowest (best) metric value to the lowest multiplied times the variance value Acceptable values are nonzero, positive integers Default value is 1, which implies equal-cost load balancing

IGRP Traffic-Share The traffic-share {balanced | min} command is used to control how traffic is distributed among IGRP load sharing routes router(config-router)#traffic-share {balanced|min} Balanced option destributes traffic proportional to the ratios of the metrics Min option specifies using routes with the minimum cost

IGRP Show IP Protocols The show ip protocols command displays parameters, filters and network information about the entire router

IGRP Show IP Protocols Example RouterA#sh ip protocols Routing Protocol is “igrp 100” Sending updates every 90 seconds, next due in 21 seconds Invalid after 270 seconds, hold down 280, flushed after 630 Outgoing update filter list for all interfaces is Incoming update filter list for all interfaces is Default networks flagged in outgoing updates Default networks accepted from incoming updates IGRP metric weight K1=1, K2=0, K3=1, K4=0, K5=0 IGRP maximum hopcount 100 IGRP maximum metric variance 1 Redistributing: igrp 100 Routing for Networks: 10.0.0.0 172.16.0.0 Routing Information Sources: Gateway Distance Last Update 10.1.1.2 100 00:01:01 Distance: (default is 100)

Show IP Protocols Fields Output Description Routing Protocol Routing protocol and autonomous system Update Rate at which updates are sent Invalid Number of seconds after which a route is declared invalid – Should be at least 3 times update value Hold-Down Number of seconds worst path routing information is surpressed – Should be at least 3 times value of update Flushed Number of seconds that must pass before route is removed from table – Should be equal to or greater than sum of invalid and holddown values

IGRP Show IP Route RouterA#sh ip route Codes: C – connected, S – static, I – IGRP, R – RIP, M – mobile, B – BGP D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2 E1 – OSPF external type 1, E2 – OSPF external type 2, E – EGP i – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-2, * - candidate default U – per-user static route, o – ODR T – traffic engineered route Gateway of last resort is not set 172.16.0.0/24 is subnetted, 1 subnets C 172.16.1.0 is directly connected, Ethernet0 10.0.0.0/24 is subnetted, 2 subnets I 10.2.2.0 [100/90956] via 10.1.1.2, 00:00:23, Serial2 C 10.1.1.0 is directly connected Serial 2 I 192.168.1.0/24 [100/90956] via 10.1.1.2, 00:00:23, Serial2

Debug IP IGRP – Transactions RouterA#debug ip igrp transactions IGRP protocol debugging is on RouterA# 00:21:06: IGRP: sending update to 255.255.255.255 via Ethernet0 (172.16.1.1) 00:21:06: network 10.0.0.0, metric=88956 00:21:06: network 192.168.1.0, metric=91056 00:21:07: IGRP: sending update to 255.255.255.255 via Serial 2 (10.1.1.1) 00:21:07: network 172.16.0.0, metric=1100 00:21:16: IGRP: received update from 10.1.1.2 on Serial2 00:21:16: subnet 10.2.2.0, metric 90956 (neighbor 88956) 00:21:16: network 192.168.1.0, metric 91056 (neighbor 89056) Disable debugging with no debug igrp transactions or no debug all

Debug IP IGRP – Events RouterA#debug ip igrp events IGRP event debugging is on RouterA# 00:23:44: IGRP: sending update to 255.255.255.255 via Ethernet0 (172.16.1.1) 00:23:44: IGRP: Update contains 0 interior, 2 system, and 0 exterior routes. 00:23:44: IGRP: Total routes in update: 2 00:23:44: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.1) 00:23:45: IGRP: Update contains 0 interior, 1 system, and 0 exterior routes. 00:23:45: IGRP: Total routes in update: 1 00:23:48: IGRP: received update from 10.1.1.2 on Serial 2 00:23:48: IGRP Update contains 1 interior, 1 system, and 0 exterior routes 00:23:48: IGRP Total routes in update: 2

Network 172.16.0.0 Fails X S2 E0 S3 S2 E0 S3 172.16.1.0 192.168.1.0 A B C S2 X E0 S3 S2 E0 S3 172.16.1.1 10.1.1.1 10.1.1.2 10.2.2.2 10.2.2.3 192.168.1.1

Network 172.16.0.0 Fails – RouterA RouterA#debug ip igrp trans IGRP protocol debugging is on RouterA# 00:31:15: %LINEPROTO – 5 - UPDOWN; Line protocol on interface Ethernet0 changed state to down 00:31:15: IGRP: edition is now 3 00:31:15: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.1) 00:31:16: network 172.16.0.0, metric=4294967295 ROUTE DOWN 00:31:16: IGRP: Update contains 0 interior, 1 system, and 0 exterior routes. 00:31:16: IGRP: Total routes in update: 1 00:31:16: IGRP: broadcasting request on Serial2 00:31:16: IGRP: received update from 10.1.1.2 on Serial2 00:31:16: subnet 10.2.2.0, metric 90956 (neighbor 88956) 00:31:16: network 172.16.0.0, metric 4294967295 (inaccessible) REVERSE POISON 00:31:16: network 192.168.1.0, metric 91056 (neighbor 89056) 00:31:16: IGRP: Update contains 1 interior, 2 system, and 0 exterior routes 00:31:16: IGRP: Total routes in update: 3

Network 172.16.0.0 Fails – RouterB RouterB#debug ip igrp trans IGRP protocol debugging is on RouterB# 1d19h: IGRP: sending update to 255.255.255.255 via Serial2 (10.1.1.2) 1d19h: subnet 10.2.2.0, metric=88956 1d19h: network 192.168.1.0, metric=89056 1d19h: IGRP: sending update to 255.255.255.255 via Serial3 (10.2.2.2) 1d19h: subnet 10.1.1.0, metric=88956 1d19h: network 172.16.0.0, metric=89056 1d19h: IGRP: received update from 10.1.1.1 on Serial2 1d19h: network 172.16.0.0, metric 4294967295 (inaccessible) POSSIBLY DOWN 1d19h: IGRP: edition is now 10 1d19h: subnet 10.2.2.0, metric 90956 1d19h: network 172.16.0.0, metric 4294967295 POISON 1d19h: network 192.168.1.0, metric 91056 1d19h: network 172.16.0.0, metric 4294967295

Holddown State – Router B RouterB#sh ip route Codes: C – connected, S – static, I – IGRP, R – RIP, M – mobile, B – BGP D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2 E1 – OSPF external type 1, E2 – OSPF external type 2, E – EGP i – IS-IS, L1 – IS-IS level-1, L2 – IS-IS level-2, * - candidate default U – per-user static route, o – ODR T – traffic engineered route Gateway of last resort is not set I 172.16.0.0/24 is possibly down, routing via 10.1.1.1, Serial2 10.0.0.0/24 is subnetted, 2 subnets C 10.1.1.0 is directly connected, Serial3 C 10.2.2.0 is directly connected, Serial3 I 192.168.1.0/24 [100/89056] via 10.2.2.3, 00:00:14, Serial3

Ping – From Router B RouterB#ping 172.16.1.1 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 172.16.1.1, timeout is 2 seconds: … Success rate is 0 percent (0/5) RouterB#

If 172.16.0.0 Comes Back Up RouterA sends another triggered update to Router B stating 172.16.0.0 is accessible with metric 89056 Even Though RouterB receives the update, the route continues in a holddown state RouterB will not remove route from holddown and update routing table until holddown timer expires However, RouterB COULD successfully ping network 172.16.0.0 and send traffic there

Unknown Subnet of a Directly Attached Network Router assumes that all subnets of a directly attached network are present in the IP routing table If a packet is received with a destination address within an unknown subnet of a directly attached network, the router assumes the subnet does not exist and drops the packet This holds true even if the routing table contains a default route This behavior can be changed with the ip classless global configuration command

IP Classless Default Route E0 S0 Network Protocol Destination Exit 10.0.0.0 172.16.0.0 10.1.0.0 10.2.2.2 Network Protocol Destination Exit Interface C RIP 10.1.0.0 10.2.0.0 172.16.0.0 via 0.0.0.0 E0 S0 Router(config)#ip classless

IP Classless The middle router will forward a packet with 10.7.1.1 as the destination address out of the default interface, E0, because ip classless is enabled

Routing Command Summary Description ip route network mask {address | interface} [distance] [permanent] Defines a static route router protocol [keyword] Enables dynamic routing protocol network network-number Allows dynamic routing protocol to advertise a route and enables the protocol on the interfaces on that network show ip protocols Displays information about the dynamic routing protocols configured on the router show ip route Displays the IP routing table debug ip rip Enables the router to display RIP routing updates as they occur variance multiplier Enables IGRP to do unequal path load sharing traffic-share {balanced | min} Tells router how to load-balance traffic on load-sharing links debug ip igrp transactions Displays IGRP transaction info as it occurs debug ip igrp events Displays IGRP events as they occur no debug all Turns off all debugging displays ip classless Allows routing protocol to send traffic to a less specific route if one is available