CCNA version 1.0 Rick Graziani Cabrillo College Ch. 7 – Distance Vector Routing Protocols Part 2 of 2: Distance Vector Routing and IGRP CCNA version 1.0 Rick Graziani Cabrillo College

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 Rick Graziani graziani@cabrillo.edu

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 Rick Graziani graziani@cabrillo.edu

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 Rick Graziani graziani@cabrillo.edu

IGRP Metrics Rick Graziani graziani@cabrillo.edu

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. Rick Graziani graziani@cabrillo.edu

Administrative Distances Rick Graziani graziani@cabrillo.edu

IGRP Metrics Rick Graziani graziani@cabrillo.edu

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. Rick Graziani graziani@cabrillo.edu

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.” Rick Graziani graziani@cabrillo.edu

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.” Rick Graziani graziani@cabrillo.edu

IGRP Timers IGRP has a number of features that are designed to enhance its stability, such as: Holddowns Split horizons Poison reverse updates Rick Graziani graziani@cabrillo.edu

IGRP Timers Update timer 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. Rick Graziani graziani@cabrillo.edu

IGRP Timers Invalid timer 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.” Rick Graziani graziani@cabrillo.edu

IGRP Timers Holddown timer 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. Rick Graziani graziani@cabrillo.edu

IGRP Timers Flush timer 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. Rick Graziani graziani@cabrillo.edu

IGRP Timers Update 90 secs – Update and Invalid timers are then reset. 270 secs - Invalid timer expires, route now “unreachable” but still in routing table until flush timer expires. Holddown timer of 280 sec begins. Holddown 280 secs – Holddown timer expires, will now accept a poorer route to same network. Still in routing table Flush 630 secs – Route will now be removed from the routing table. My testing shows that the flush timer starts after the first 90 second update is missed. 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 Rick Graziani graziani@cabrillo.edu

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. Rick Graziani graziani@cabrillo.edu

Configuring IGRP Same network commands as RIP. IGRP “AS” number must be the same on all routers. Rick Graziani graziani@cabrillo.edu

Configuring IGRP timers basic (IGRP) Router(config-router)#router igrp 100 Router(config-router)#timers basic update invalid holddown flush [sleeptime] Router(config-router)# no timers basic 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. Rick Graziani graziani@cabrillo.edu

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)#no router rip Enable IGRP Suggestion: Remove RIP configuration from routers even though the administrative distance will prefer RIP Rick Graziani graziani@cabrillo.edu

Verifying IGRP Rick Graziani graziani@cabrillo.edu

Verifying IGRP Rick Graziani graziani@cabrillo.edu

Verifying IGRP Rick Graziani graziani@cabrillo.edu

Verifying IGRP Rick Graziani graziani@cabrillo.edu

Verifying IGRP Rick Graziani graziani@cabrillo.edu

Troubleshooting IGRP Rick Graziani graziani@cabrillo.edu

Troubleshooting IGRP Rick Graziani graziani@cabrillo.edu

Troubleshooting IGRP Rick Graziani graziani@cabrillo.edu

Domains… Rick’s extra information on autonomous systems…(FYI only!) Two types of autonomous systems: 1. Process domain 2. Routing domain Rick Graziani graziani@cabrillo.edu

Domains… 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. Rick Graziani graziani@cabrillo.edu

Domains… 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. Rick Graziani graziani@cabrillo.edu

Rick Graziani graziani@cabrillo.edu

Summary But there is still more! Rick Graziani graziani@cabrillo.edu

IGRP Metric Information (and for EIGRP as well!)

Metric Calculation 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. Rick Graziani graziani@cabrillo.edu

Metric Calculation 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. Rick Graziani graziani@cabrillo.edu

Metric Calculation bandwidth delay reliability 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 Rick Graziani graziani@cabrillo.edu

Metric Calculation (Review) 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 EIGRP bandwidth is in kbps Rick Graziani graziani@cabrillo.edu

IGRP Viva la difference! EIGRP Calculated values (cumulative) displayed in routing table (show ip route). EIGRP values are 256 times greater. Rick Graziani graziani@cabrillo.edu

Displaying Interface Values 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 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) 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) Rick Graziani graziani@cabrillo.edu

Displaying Interface Values 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 Routing Table Metric Default: Slowest of bandwidth plus the sum of the delays of all outgoing interfaces from “this router” to the destination network. Rick Graziani graziani@cabrillo.edu

Metric Calculation 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. Rick Graziani graziani@cabrillo.edu

Metric Calculation 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 Rick Graziani graziani@cabrillo.edu

Metric Calculation 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. Rick Graziani graziani@cabrillo.edu

Metric Calculation 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 Rick Graziani graziani@cabrillo.edu

Metric Calculation 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: 107, (10,000,000/bandwidth kbps), whereas with OSPF it was 108 (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 Rick Graziani graziani@cabrillo.edu

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. Rick Graziani graziani@cabrillo.edu

Metric Calculation bandwidth delay reliability 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 Rick Graziani graziani@cabrillo.edu

From Casablanca to 172.20.40.0/24 Rick Graziani graziani@cabrillo.edu

From Casablanca to 172.20.40.0/24 Using BWIGRP and DLYIGRP to calculate the IGRP metric: The slowest bandwidth has the highest BWIGRP value. IGRP metric = highest BWIGRP + total of the DLYIGRP = 19,531 + (100 + 2,000 + 2,000 + 100) = 19,531 + 4,200 = 23,731 Rick Graziani graziani@cabrillo.edu

Calculating the IGRP Metric Using the Raw Values: Bandwidth and Delay

From Casablanca to 172.20.40.0/24 Rick Graziani graziani@cabrillo.edu

Calculating Bandwidth So how is Bandwidth, BWIGRP, calculated? The bandwidth metric is calculated by taking 107 (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 107 (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 BWIGRP along the route Rick Graziani graziani@cabrillo.edu

Calculating Delay So how is Delay, DLYIGRP, 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 DLYIGRP, the total Delays along the route! Rick Graziani graziani@cabrillo.edu

Slowest Bandwidth + Sum of Delays IGRP metric = Bandwidth + Delay IGRP metric = 19,531 + 4,200 = 23,731 IF we were using RIP, the RIP metric would be 3 hops. Rick Graziani graziani@cabrillo.edu

show ip route 172.20.40.0 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. Rick Graziani graziani@cabrillo.edu

So, what about Reliability and Load?

Reliability and Load 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 Rick Graziani graziani@cabrillo.edu

Reliability and Load 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! Rick Graziani graziani@cabrillo.edu

Reliability and Load bandwidth delay reliability 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 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) Rick Graziani graziani@cabrillo.edu

Reliability and Load 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. Rick Graziani graziani@cabrillo.edu

Reliability and Load bandwidth delay reliability 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 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) Rick Graziani graziani@cabrillo.edu

Reliability and Load k1 for bandwidth k2 for load k3 for delay IGRP metric = [k1* BWIGRP(minimum) + (k2* BWIGRP(minimum))/(256-LOAD) + k3* DLYIGRP(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 Rick Graziani graziani@cabrillo.edu

Reliability and Load 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. Rick Graziani graziani@cabrillo.edu

IGRP and EIGRP: A migration path Classful Routing Protocol Classless Routing Protocol VLSM, CIDR bandwidth = (10,000,000/bandwidth kbps) delay = delay/10 24 bit metric for bandwidth and delay bandwidth = (10,000,000/bandwidth kbps) * 256 delay = (delay/10) * 256 32 bit metric for bandwidth and delay Maximum Hop Count = 255 Maximum Hop Count = 224 No differentiation between internal and external routes. Outside routes (redistributed) are tagged as external routes. Automatic redistribution between IGRP and EIGRP as long as “AS” numbers are the same. Rick Graziani graziani@cabrillo.edu

CCNA version 1.0 Rick Graziani Cabrillo College Ch. 7 – Distance Vector Routing Protocols Part 2 of 2: Distance Vector Routing and IGRP CCNA version 1.0 Rick Graziani Cabrillo College