Module 7 – Distance Vector Routing Protocols
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Module 7 – Distance Vector Routing Protocols Presentation Transcript

  • 1. Ch. 7 – Distance Vector Routing Protocols Part 2 of 2: Distance Vector Routing and IGRP CCNA version 1.0 Rick Graziani Cabrillo College
  • 2. Note to instructors
    • If you have downloaded this presentation from the Cisco Networking Academy Community FTP Center, this may not be my latest version of this PowerPoint.
    • For the latest PowerPoints for all my CCNA, CCNP, and Wireless classes, please go to my web site:
    • http://www.cabrillo.cc.ca.us/~rgraziani/
        • The username is cisco and the password is perlman for all of my materials.
    • If you have any questions on any of my materials or the curriculum, please feel free to email me at graziani@cabrillo.edu (I really don’t mind helping.) Also, if you run across any typos or errors in my presentations, please let me know.
    • I will add “(Updated – date )” next to each presentation on my web site that has been updated since these have been uploaded to the FTP center.
    • Thanks! Rick
  • 3. IGRP Features
    • IGRP is a distance vector routing protocol developed by Cisco.
    • IGRP sends routing updates at 90 second intervals, advertising networks for a particular autonomous system.
    • Key design characteristics of IGRP are a follows:
      • The versatility to automatically handle indefinite, complex topologies
      • The flexibility needed to segment with different bandwidth and delay characteristics
      • Scalability for functioning in very large networks
  • 4. IGRP Features
    • By default, the IGRP routing protocol uses bandwidth and delay as metrics.
    • Additionally, IGRP can be configured to use a combination of variables to determine a composite metric.
    • Those variables include:
      • Bandwidth
      • Delay
      • Load
      • Reliability
  • 5. IGRP Metrics
  • 6. IGRP Metrics
    • The metrics that IGRP uses are:
      • Bandwidth – The lowest bandwidth value in the path
      • Delay – The cumulative interface delay along the path
      • Reliability – The reliability on the link towards the destination as determined by the exchange of keepalives
      • Load – The load on a link towards the destination based on bits per second
      • NO… MTU – The Maximum Transmission Unit value of the path. MTU has never been used by IGRP or EIGRP as a routing metric.
    • IGRP has an administrative distance of 100 , more “trustworthy” than RIP at 120.
    • This means a Cisco router will prefer an IGRP learned route over a RIP learned route to the same network.
  • 7. Administrative Distances
  • 8. IGRP Metrics
  • 9. IGRP Routes
    • Interior “Interior routes are routes between subnets of a network attached to a router interface. If the network attached to a router is not subnetted, IGRP does not advertise interior routes.”
    • Clarification
    • IGRP also advertises three types of routes:
      • interior, system, and exterior.
    • Interior routes are routes between subnets in the network attached to a router interface.
    • If the network attached to a router is not subnetted, IGRP does not advertise interior routes.
  • 10. IGRP Routes
    • System “System routes are routes to networks within an autonomous system. The Cisco IOS software derives system routes from directly connected network interfaces and system route information provided by other IGRP-speaking routers or access servers. System routes do not include subnet information.”
  • 11. IGRP Routes
    • Exterior “Exterior routes are routes to networks outside the autonomous system that are considered when identifying a gateway of last resort. The Cisco IOS software chooses a gateway of last resort from the list of exterior routes that IGRP provides. The software uses the gateway (router) of last resort if a better route is not found and the destination is not a connected network. If the autonomous system has more than one connection to an external network, different routers can choose different exterior routers as the gateway of last resort.”
  • 12. IGRP Timers
    • IGRP has a number of features that are designed to enhance its stability, such as:
      • Holddowns
      • Split horizons
      • Poison reverse updates
  • 13. IGRP Timers
    • The update timer specifies how frequently routing update messages should be sent.
    • The IGRP default for this variable is 90 seconds .
    • A random jitter variable of 20% is subtracted from each update time to prevent update timer synchronization.
    • IGRP updates will vary from 72 to 90 seconds.
    Update timer
  • 14. IGRP Timers
    • The invalid timer specifies how long a router should wait in the absence of routing-update messages about a specific route before declaring that route invalid (unreachable), but still in the routing table .
    • The IGRP default for this variable is three times the update period or 270 seconds .
    • Then placed in the holddown state.
    • “ If I haven’t heard from you in 270 seconds, I am considering this route as unreachable, I will start the holddown timer, but I will keep it in the routing table until the flush timer expires.”
    Invalid timer
  • 15. IGRP Timers
    • The holddown timer specifies the amount of time for which information about poorer routes are ignored.
    • Zinin: “Holddown specifies the number of seconds that a route must spend in holddown state after expiration of the Invalid Timer.”
    • The IGRP default for this variable is three times the update timer period plus 10 seconds = 280 seconds .
    • The original route is still in the routing table but marked as unreachable, until the flush timer expires.
    Holddown timer
  • 16. IGRP Timers
    • Finally, the flush timer indicates how much time should pass before a route is flushed from the routing table.
    • The IGRP default is seven times the routing update timer or 630 seconds .
    • Zinin: “Flush specifies the number of seconds that a route must remain in the routing table in the garbage collection state after it exits the holddown state.”
    • Each time an update is received the invalid and flush timers are reset .
    • If the invalid timer expires before another update is heard, the route is marked as unreachable , but remains in the routing table.
    • If the flush timer then expires before another update is heard, the route will be deleted from the routing table .
    Flush timer
  • 17. IGRP Timers
    • Update timer : how frequently routing update messages should be sent
    • Invalid timer : how long a router should wait in the absence of routing-update messages about a specific route before declaring that route invalid (unreachable), but still in the routing table
    • Holddown timer : specifies the amount of time for which information about poorer routes are ignored.
    • Flush timer : how much time should pass before a route is flushed from the routing table
    My testing shows that the flush timer starts after the first 90 second update is missed. 90 secs – Update and Invalid timers are then reset. Update 270 secs - Invalid timer expires, route now “unreachable” but still in routing table until flush timer expires. Holddown timer of 280 sec begins. Invalid 280 secs – Holddown timer expires, will now accept a poorer route to same network. Still in routing table Holddown 630 secs – Route will now be removed from the routing table. Flush
  • 18. IGRP Timers
    • All timers begin at the same time.
      • Update timer = 90 seconds
      • Invalid timer = 270 seconds
      • Holddown timer = 280 seconds
      • Flush timer = 630 seconds
    • Today, IGRP is showing its age, it lacks support for variable length subnet masks (VLSM).
    • Enhanced IGRP (EIGRP) supports VLSM.
  • 19. Configuring IGRP
    • Same network commands as RIP.
    • IGRP “AS” number must be the same on all routers.
  • 20. Configuring IGRP
    • timers basic (IGRP)
    • To adjust Interior Gateway Routing Protocol (IGRP) network timers, use the timers basic router configuration command. To restore the default timers, use the no form of this command.
    Router(config-router)# router igrp 100 Router(config-router)# timers basic update invalid holddown flush [ sleeptime ] Router(config-router)# no timers basic
  • 21. Migrating from RIP to IGRP
    • Router(config)# router rip
    • Router(config-router)# network 172.16.0.0
    • Router(config-router)# network 192.168.1.0
    • Router(config-router)# exit
    • Router(config)# router igrp 10
    • Router(config-router)# network 172.16.0.0
    • Router(config-router)# network 192.168.1.0
    • Router(config-router)# exit
    • Router(config)# no router rip
    • Enable IGRP
    • Suggestion: Remove RIP configuration from routers even though the administrative distance will prefer RIP
  • 22. Verifying IGRP
  • 23. Verifying IGRP
  • 24. Verifying IGRP
  • 25. Verifying IGRP
  • 26. Verifying IGRP
  • 27. Troubleshooting IGRP
  • 28. Troubleshooting IGRP
  • 29. Troubleshooting IGRP
  • 30.
    • Rick’s extra information on autonomous systems …(FYI only!)
    • Two types of autonomous systems:
    • 1. Process domain
    • 2. Routing domain
    Domains…
  • 31.
    • Process domain
    • A single IGP (Interior Gateway Protocol) process that is autonomous from other IGP processes.
    • IGRP autonomous systems are also known as a process domains.
    • Redistribution is used to route between these types of autonomous systems.
    Domains…
  • 32.
    • Routing domain
    • A system of one or more IGPs (Interior Gateway Protocols) that is autonomous from other IGP systems.
    • An EGP (Exterior Gateway Protocol) like BGP is used to route between these types of autonomous systems.
    Domains…
  • 33.  
  • 34. Summary But there is still more!
  • 35. IGRP Metric Information (and for EIGRP as well!)
  • 36.
    • The metrics used by IGRP in making routing decisions are ( lower the metric the better ):
    • bandwidth
    • delay
    • load
    • reliability
    • By default, IGRP uses only:
    • Bandwidth
    • Delay
    • Analogies :
    • Think of bandwidth as the width of the pipe
    • and
    • delay as the length of the pipe .
    • Bandwidth is a the carrying capacity
    • Delay is the end-to-end travel time .
    Metric Calculation
  • 37.
    • If these are the default:
    • bandwidth (default)
    • delay (default)
    • When are these used?
    • load
    • reliability
    • Only when configured by the network administrator to do so!
    • IGRP also tracks (but does not use in its metric calculation):
    • MTU (Maximum Transmission Unit)
    • Hop Count
    • Use show interface command to view the metrics used on a specific interface that is routing EIGRP.
    • These are the raw values .
    Metric Calculation
  • 38. Metric Calculation Router> show interfaces s1/0 Serial1/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) <output omitted> bandwidth delay reliability load
  • 39. Metric Calculation (Review) EIGRP
    • k1 for bandwidth
    • k2 for load
    • k3 for delay
    • k4 and k5 for Reliability
    • Router(config-router)# metric weights tos k1 k2 k3 k4 k5
    bandwidth is in kbps
  • 40. Viva la difference! IGRP EIGRP Calculated values (cumulative) displayed in routing table (show ip route). EIGRP values are 256 times greater.
  • 41. Displaying Interface Values
    • shows reliability as a fraction of 255, for example (higher is better):
    • rely 190/255 (or 74% reliability)
    • rely 234/255 (or 92% reliability)
    • rely 255/255 (or 100% reliability)
    Router> show interface s0/0 Serial0/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) <output omitted> Bandwidth Delay Reliability Load shows load as a fraction of 255, for example (lower is better): load 10/255 (or 3% loaded link) load 40/255 (or 16% loaded link) load 255/255 (or 100% loaded link)
  • 42. Displaying Interface Values
    • Routing Table Metric
    • Default: Slowest of bandwidth plus the sum of the delays of all outgoing interfaces from “this router” to the destination network.
    Router> show interface s0/0 Serial0/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) <output omitted> Bandwidth Delay Reliability Load
  • 43.
    • Bandwidth
    • Expressed in kilobits ( show interface )
    • This is a static number and used for metric calculations only.
    • Does not necessarily reflect the actual bandwidth of the link.
    • It is an information parameter only .
    • You cannot adjust the actual bandwidth on an interface with this command.
    • Use the show interface command to display the raw value
    • The default values:
    • Default bandwidth of a Cisco interface depends on the type of interface.
    • Default bandwidth of a Cisco serial interface is 1544 kilobits or 1,544,000 bps (T1), whether that interface is attached to a T1 line (1.544 Mbps) or a 56K line.
    • IGRP metric uses the slowest bandwidth of all of the outbound interfaces to the destination network.
    Metric Calculation
  • 44.
    • Changing the bandwidth informational parameter:
    • The bandwidth can be changed using:
    • Router(config-if)# bandwidth kilobits
    • To restore the default value:
    • Router(config-if)# no bandwidth
    Metric Calculation
  • 45.
    • Delay
    • Like bandwidth, delay it is a static number .
    • Expressed in microseconds , millionths of a second
    • (Uses the Greek letter mu with an S,  S, NOT “ms” which is millisecond or thousandths of a second )
    • Use the show interface command to display the raw value
    • It is an information parameter only .
    • The default values:
    • The default delay value of a Cisco interface depends upon the type of interface .
    • Default delay of a Cisco serial interface is 20,000 microseconds , that of a T1 line.
    • IGRP metric uses the sum of all of the delays of all of the outbound interfaces to the destination network.
    Metric Calculation
  • 46.
    • Changing the delay informational parameter:
    • The delay can be changed using:
    • Router(config-if)# delay tens-of-  S
    • (microseconds)
    • Example of changing the delay on a serial interface to 30,000 microseconds :
    • Router(config-if)# delay 3000
    • To restore the 20,000 microsecond default value:
    • Router(config-if)# no delay
    Metric Calculation
  • 47.
    • IGRP
    • bandwidth = (10,000,000/ bandwidth )
    • delay = delay /10
    • Note: EIGRP
    • bandwidth = (10,000,000/ bandwidth ) * 256
    • delay = ( delay /10) * 256
    • Note: The reference-bandwidth
    • For both IGRP and EIGRP: 10 7 , (10,000,000/bandwidth kbps), whereas with OSPF it was 10 8 (100,000,000/bandwidth)
    • The difference :
    • IGRP metric is 24 bits long
    • EIGRP metric is 32 bits long
    • EIGRP metric is 256 times greater for the same route
    • EIGRP allows for finer comparison of potential routes
    Metric Calculation
  • 48. IGRP Metrics Values displayed in show interface commands and sent in routing updates. Calculated values (cumulative) displayed in routing table (show ip route). EIGRP values are 256 times greater.
  • 49. Metric Calculation Router> show interfaces s1/0 Serial1/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) <output omitted> bandwidth delay reliability load
  • 50. From Casablanca to 172.20.40.0/24
  • 51.
    • Using BW IGRP and DLY IGRP to calculate the IGRP metric:
    • The slowest bandwidth has the highest BW IGRP value.
    • IGRP metric
    • = highest BW IGRP + total of the DLY IGRP
    • = 19,531 + (100 + 2,000 + 2,000 + 100)
    • = 19,531 + 4,200
    • = 23,731
    From Casablanca to 172.20.40.0/24
  • 52. Calculating the IGRP Metric Using the Raw Values: Bandwidth and Delay
  • 53. From Casablanca to 172.20.40.0/24
  • 54.
    • So how is Bandwidth, BW IGRP , calculated?
    • The bandwidth metric is calculated by taking 10 7 (10,000,000) and dividing it by the slowest bandwidth metric along the route to the destination .
    • This is known as taking the inverse of the bandwidth scaled by a factor of 10 7 (10,000,000)
    • The lowest bandwidth on the route is 512K or 512 (measured in kilobits), the outgoing interface of the Quebec router.
    • Divide 10,000,000 by 512 and you get the bandwidth!
    • Bandwidth = 10,000,000/512
    • = 19,531
    • Which is the lowest BW IGRP along the route
    Calculating Bandwidth
  • 55.
    • So how is Delay, DLY IGRP , calculated?
    • Delay is the total sum of delays on the outgoing interfaces , in 10-microsecond units
    • The sum of the delays on each of the outgoing interfaces between Casablanca and Yalta, from 172.20.1.0/24 through 172.20.40.0/24 is:
    • 1,000 (Casablanca) + 20,000 (Teheran) + 20,000 (Quebec) + 1,000 (Yalta) = 42,000
    • We need this in 10-microsecond units:
    • = (1,000/10)+(20,000/10) + (20,000/10) + (1,000/10)
    • = 100 + 2,000 + 2,000 + 100
    • or
    • = (1,000 + 20,000 + 20,000 +1,000) / 10
    • In either case the total sum is:
    • Delay = 4,200
    • Which is the total of the DLY IGRP , the total Delays along the route!
    Calculating Delay
  • 56.
    • IGRP metric = Bandwidth + Delay
    • IGRP metric = 19,531 + 4,200
    • = 23,731
    • IF we were using RIP, the RIP metric would be 3 hops .
    Slowest Bandwidth + Sum of Delays
  • 57.
    • Casablanca# show ip route 172.20.40.0
    • Known via igrp 1, distance 100, metric 23,731
    • 172.20.1.2, from 172.20.1.2 on Ethernet 0
    • Route metric is 23,731
    • Total delay is 42,000 microseconds,
    • minimum bandwidth is 512 Kbit
    • ...
    • Not to be redundant, but if we were using RIP, the RIP metric would be 3 hops.
    show ip route 172.20.40.0
  • 58. So, what about Reliability and Load?
  • 59.
    • The metrics used by EIGRP in making routing decisions are ( lower the metric the better ):
    • bandwidth
    • delay
    • load
    • reliability
    • By default, EIGRP uses only:
    • Bandwidth
    • Delay
    Reliability and Load
  • 60.
    • Reliability
    • Reliability is measure dynamically
    • Uses error rate for measurement
    • Reflects the total outgoing error rates of the interfaces along the route
    • Calculated on a five minute weighted average, so not to allow sudden peaks and valleys to make a significant impact
    • Expressed as an 8 bit number
    • 255 is a 100% reliable link
    • 1 is a minimally reliable link
    • Higher the better!
    Reliability and Load
  • 61.
    • shows reliability as a fraction of 255, for example:
    • rely 190/255 (or 74% reliability)
    • rely 234/255 (or 92% reliability)
    • rely 255/255 (or 100% reliability)
    Reliability and Load Router> show interfaces s1/0 Serial1/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) <output omitted> bandwidth delay reliability load
  • 62.
    • Load
    • Load is measure dynamically
    • Uses channel occupancy for measurement
    • Reflects the total outgoing load of the interfaces along the route
    • Calculated on a five minute weighted average, so not to allow sudden peaks and valleys to make a significant impact
    • Expressed as an 8 bit number
    • 255 is a 100% loaded link
    • 1 is a minimally loaded link
    • Lower the better!
    • Note: Even though load and reliability are dynamically changing values, EIGRP will not recalculate the route metric when these parameters change.
    Reliability and Load
  • 63.
    • shows load as a fraction of 255, for example:
    • load 10/255 (or 3% loaded link)
    • load 40/255 (or 16% loaded link)
    • load 255/255 (or 100% loaded link)
    Reliability and Load Router> show interfaces s1/0 Serial1/0 is up, line protocol is up Hardware is QUICC Serial Description: Out to VERIO Internet address is 207.21.113.186/30 MTU 1500 bytes, BW 1544 Kbit, DLY 20000 usec, rely 255/255, load 246/255 Encapsulation PPP, loopback not set Keepalive set (10 sec) <output omitted> bandwidth delay reliability load
  • 64.
    • IGRP metric =
    • [k1* BW IGRP(minimum) +
    • (k2* BW IGRP(minimum) )/(256- LOAD ) +
    • k3* DLY IGRP(sum) ] *
    • [k5/ RELIABILITY + k4)]
    • k2 metric effects LOAD
    • k4 and k5 effects RELIABILITY
    • Multiply Reliability only if > 0
    • Default :
    • k1=k3=1 and k2=k4=k5=0
    • You may change the k values to change what you want to give more or less weight to.
      • k1 for bandwidth
      • k2 for load
      • k3 for delay
      • k4 and k5 for Reliability
    • Higher the k value, the more that part of the metric is used to calculate the overall IGRP metric
    Reliability and Load
  • 65.
    • Turning the knobs:
    • We can use the other metrics of Reliability and Load by adjusting their k values to something greater than “0”
    • The command to adjust the k values is:
    • Router(config-router)# metric weights tos k1 k2 k3 k4 k5
    • Notes :
    • tos is always set to 0; at one time it was Cisco’s intent to use it, but it was never implemented
    • EIGRP neighbors must agree on K values to establish an adjacency and to avoid routing loops.
    • Caution!
    • Know what the impact will be before changing the defaults.
    • It can give you unexpected results if you do not know what you are doing!
    • If you modify the weights, you should configure all routers so they are all using the same weight values.
    Reliability and Load
  • 66. IGRP and EIGRP: A migration path Automatic redistribution between IGRP and EIGRP as long as “AS” numbers are the same. Outside routes (redistributed) are tagged as external routes. No differentiation between internal and external routes. Maximum Hop Count = 224 Maximum Hop Count = 255 bandwidth = (10,000,000/ bandwidth kbps ) * 256 delay = ( delay /10) * 256 32 bit metric for bandwidth and delay bandwidth = (10,000,000/ bandwidth kbps ) delay = delay /10 24 bit metric for bandwidth and delay
    • Classless Routing Protocol
    • VLSM, CIDR
    Classful Routing Protocol EIGRP IGRP
  • 67. Ch. 7 – Distance Vector Routing Protocols Part 2 of 2: Distance Vector Routing and IGRP CCNA version 1.0 Rick Graziani Cabrillo College