What is OSPF Throttling

introduction

This document describes how to create a preferred route by influencing the Enhanced Interior Gateway Routing Protocol (EIGRP) metrics. In view of the topology shown in the network diagram, this document describes several possibilities to influence the IP data traffic from the clients to the servers, so that the path R1> R2> R3 is preferred. The aim is to convert the path R1> R2> R4 into a data backup that is only used in the event of an error with R3.

requirements

conditions

This document requires a basic understanding of IP routing and EIGRP routing. For more information on IP routing and EIGRP, see the following documents:

Components used

The information in this document is based on these software and hardware versions.

  • EIGRP is powered by the Cisco IOS® Software version 9.21 and higher supported. The information in this document is based on Cisco IOS software version 12.3 (3).

  • EIGRP can be configured on all routers (such as the Cisco 2500 Series and Cisco 2600 Series) and on all Layer 3 switches.

The information in this document was produced by the devices in a specific laboratory environment. All devices used in this document started with an empty (standard) configuration. With your network up and running, make sure you understand the potential implications of a command.

Conventions

For more information on document conventions, see the.

Background information

There are several methods of setting a preferred route by affecting EIGRP metrics. This document describes these methods and describes their advantages and disadvantages. This document also covers the effects of changing the bandwidth, although it is not a viable way to change the path in this example.

Click the network diagram to view it in a separate browser window, which will be used for reference later in this document.

Two of the commands used in this document to check EIGRP behavior are the Topology show ip eigrp and the Commands show ip eigrp topology network-ipsubnet mask.

  

When you use the show ip eigrp topology or the command show ip eigrp topology network-ip subnet mask output from your Cisco device, you can use Cisco CLI Analyzer Use (registered customers only) to view potential issues and fixes. To Cisco CLI Analyzer (registered customers only), you must be logged in and activate JavaScript in your web browser.

Background - EIGRP Metrics - Fundamentals

EIGRP updates contain five metrics: minimum bandwidth, delay, load, reliability, and MTU (Maximum Transmission Unit). By default, of these five metrics, only minimal bandwidth and delay are used to calculate the best path. Unlike most metrics, the minimum bandwidth is set to the minimum bandwidth of the entire path, and it does not reflect how many hops or low-bandwidth links there are in the path. The delay is a cumulative value that increases by the delay value of each segment in the path. For more information on EIGRP metrics, see the Enhanced Interior Gateway Routing Protocol white paper.

Possible configurations

These configurations can be used to set a preferred route.

Configuration for standard load balancing

R1

R1 # show run Current configuration: 640 bytes! version 12.3! hostname R1! interface Serial0 no ip address encapsulation frame-relay ! --- Enables Frame Relay encapsulation. ! interface Serial0.201 point-to-point ! --- Enables a point-to-point link on the sub-interface. ip address 10.1.1.1 255.255.255.0 frame-relay interface-dlci 201 ! --- Assigns a data-link connection identifier (DLCI)
! --- to a Frame Relay sub-interface.
! router eigrp 1 network 10.0.0.0! end

Note: The frame relay switch is hidden in the network diagram.

R1 # show 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 - ISIS level-1, L2 - ISIS level-2, * - candidate default U - per-user static route, o - ODR Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets D 10.1.3.0 [90/2221056] via 10.1.1.2, 00:07:08, Serial0.201 D 10.1.2.0 [90/2195456] via 10.1.1.2, 00:07:08, Serial0.201 C 10.1.1.0 is directly connected, Serial0.201 R1 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 2221056 Routing Descriptor Blocks: 10.1.1.2 (Serial0.201), from 10.1 .1.2, Send flag is 0x0 Composite metric is (2221056/307200), Route is Internal Vector metric: Minimum bandwidth is 1544 Kbit Total delay is 22000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 2

R2

R2 # show run Current configuration: 618 bytes! version 12.3! hostname R2! interface Ethernet0 ip address 10.1.2.2 255.255.255.0 no ip directed-broadcast! ! interface Serial0 no ip address encapsulation frame-relay! interface Serial0.101 point-to-point ip address 10.1.1.2 255.255.255.0 frame-relay interface-dlci 101! router eigrp 1 network 10.0.0.0! end R2 # show 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 - ISIS, L1 - ISIS level-1, L2 - ISIS level-2, * - candidate default U - per -user static route, o - ODR Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets D 10.1.3.0 [90/307200] via 10.1.2.4, 00:03:47, Ethernet0 [90/307200] via 10.1.2.3, 00:03:48, Ethernet0 C 10.1.2.0 is directly connected, Ethernet0 C 10.1.1.0 is directly connected, Serial0.101

Note: R2 has two equal cost paths to 10.1.3.0/24 to R3 (10.1.2.3) and R4 (10.1.2.4).

R2 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 2 Successor (s), FD is 307200 Routing Descriptor Blocks: 10.1.2.3 (Ethernet0), from 10.1.2.3 , Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1 10.1.2.4 (Ethernet0), from 10.1.2.4, Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1

Note: Both paths have the same composite metric (distance / reported distance). The "Feasible Distance" (FD) for "R1" is announced, which then becomes the "Reported Distance" for R1.

R3

R3 # show run Current configuration: 556 bytes! version 12.3! hostname R3! interface Ethernet0 / 0 ip address 10.1.2.3 255.255.255.0 no ip directed-broadcast! interface Ethernet0 / 1 ip address 10.1.3.3 255.255.255.0 no ip directed-broadcast! router eigrp 1 network 10.0.0.0! end R3 # show 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 - ISIS, L1 - ISIS level-1, L2 - ISIS level-2, ia - ISIS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets C 10.1.3.0 is directly connected, Ethernet0 / 1 C 10.1 .2.0 is directly connected, Ethernet0 / 0 D 10.1.1.0 [90/20537600] via 10.1.2.2, 00:16:14, Ethernet0 / 0 R3 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 281600 Routing Descriptor Blocks: 0.0.0.0 (Ethernet0 / 1), from Connected , Send flag is 0x0 Composite metric is (281600/0), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 1000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 0 10.1. 2.4 (Ethernet0 / 0), from 10.1.2.4, Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1 / 255 Minimum MTU is 1500 Hop count is 1 R3 # show interface ethernet0 / 1 Ethernet0 / 1 is up, line protocol is up Hardware is AmdP2, address is 0050.7329.52e1 (bia 0050.7329.52e1) Internet address is 10.1.3.3/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:02, output 00:00 : 01, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size / max / drops / flushes); Total output drops: 0 Queuing strategy: fifo Output queue: 0/40 (size / max) 5 minute input rate 0 bits / sec, 0 packets / sec 5 minute output rate 0 bits / sec, 0 packets / sec 291 packets input, 28402 bytes, 0 no buffer Received 283 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 500 packets output, 50876 bytes, 0 underruns 0 output errors, 0 collisions, 2 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out

R4

R4 # show run Current configuration: 549 bytes! version 12.3! hostname R4! interface Ethernet0 / 0 ip address 10.1.2.4 255.255.255.0 no ip directed-broadcast! interface Ethernet0 / 1 ip address 10.1.3.4 255.255.255.0 no ip directed-broadcast! router eigrp 1 network 10.0.0.0! end R4 # show 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 - ISIS, L1 - ISIS level-1, L2 - ISIS level-2, IA - ISIS inter area * - candidate default, U - per-user static route, o - ODR P - periodic downloaded static route Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets C 10.1.3.0 is directly connected, Ethernet0 / 1 C 10.1 .2.0 is directly connected, Ethernet0 / 0 D 10.1.1.0 [90/20537600] via 10.1.2.2, 00:17:08, Ethernet0 / 0 R4 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 281600 Routing Descriptor Blocks: 0.0.0.0 (Ethernet0 / 1), from Connected , Send flag is 0x0 Composite metric is (281600/0), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 1000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 0 10.1. 2.3 (Ethernet0 / 0), from 10.1.2.3, Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1 / 255 Minimum MTU is 1500 Hop count is 1

Changing the parameter for the interface delay for R4

Since changes to the delay metric are propagated to all downstream routers, changing the parameter for the interface delay is the preferred method to influence the path selection for the following two scenarios:

  • The Ethernet segment 10.1.3.0/24 only contains servers, and there are no other subnets behind the 10.1.3.0/24 subnet. (This configuration is ideal for a server farm.)

  • You want to influence the path selection for all routes that were learned via EIGRP neighbors in segment 10.1.3.0/24.

  1. Check the interface delay before making any changes.

    It is currently set to the same as R3 as shown here.

    R4 # show interface ethernet0 / 1 Ethernet0 / 1 is up, line protocol is up Hardware is AmdP2, address is 0050.7329.5321 (bia 0050.7329.5321) Internet address is 10.1.3.4/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:02, output 00: 00:02, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size / max / drops / flushes); Total output drops: 0 Queuing strategy: fifo Output queue: 0/40 (size / max) 5 minute input rate 0 bits / sec, 0 packets / sec 5 minute output rate 0 bits / sec, 0 packets / sec 284 packets input, 27914 bytes, 0 no buffer Received 276 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 482 packets output, 49151 bytes, 0 underruns 0 output errors, 0 collisions, 2 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
  2. Change the delay value for segment 10.1.3.0/24.

    You need to be careful when choosing the new delay. You don't want to increase the delay to a point where R2 no longer sees the route as a possible successor.

    R4 # configure terminal Enter configuration commands, one per line. End with CNTL / Z. R4 (config) # interface ethernet0 / 1 R4 (config-if) # delay 120! --- Delay is entered in tens of microseconds. R4 (config-if) # end R4 #
  3. Confirm that the delay for this interface has been changed to 1200 microseconds.

    R4 # show interface ethernet0 / 1 Hardware is AmdP2, address is 0050.7329.5321 (bia 0050.7329.5321) Internet address is 10.1.3.4/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1200 usec, reliability 255/255, txload 1/255, rxload 1/255 Encapsulation ARPA, loopback not set Keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:03, output 00: 00:00, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size / max / drops / flushes); Total output drops: 0 Queuing strategy: fifo Output queue: 0/40 (size / max) 5 minute input rate 0 bits / sec, 0 packets / sec 5 minute output rate 0 bits / sec, 0 packets / sec 345 packets input, 33508 bytes, 0 no buffer Received 333 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored 0 input packets with dribble condition detected 575 packets output, 57863 bytes, 0 underruns 0 output errors, 0 collisions, 2 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
  4. Make sure that R2 only has one "best" route to 10.1.3.0 via R3.

    R2 # show 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 - ISIS, L1 - ISIS level-1, L2 - ISIS level-2, * - candidate default U - per -user static route, o - ODR Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets D 10.1.3.0 [90/307200] via 10.1.2.3, 00:02:43, Ethernet0 C 10.1.2.0 is directly connected, Ethernet0 C 10.1.1.0 is directly connected, Serial0.101 R2 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 307200 Routing Descriptor Blocks: 10.1.2.3 (Ethernet0), from 10.1.2.3, Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1 10.1.2.4 (Ethernet0), from 10.1.2.4, Send flag is 0x0 Composite metric is (312320 /286720), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2200 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1

    The command show ip eigrp topology shows that the delay metric specified by R4 has increased by 200 (to 2200 microseconds) as expected. This increase results in the two routes having different costs and R2 not being load balanced.

    Note: Since the distance given by R4 (286720) is less than the distance given by R2 (the achievable distance 307200), the path is considered to be loop-free. Since the path announced by R4 is considered to be loop-free, it is a practicable successor and will be installed immediately when R3 ends the advertisement for a route after 10.1.3.0/24.

    R1 # show 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 - ISIS, L1 - ISIS level-1, L2 - ISIS level-2, * - candidate default U - per -user static route, o - ODR Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets D 10.1.3.0 [90/2221056] via 10.1.1.2, 00:25:27, Serial0.201 D 10.1 .2.0 [90/2195456] via 10.1.1.2, 00:25:27, Serial0.201 C 10.1.1.0 is directly connected, Serial0.201 R1 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 2221056 Routing Descriptor Blocks: 10.1.1.2 (Serial0.201), from 10.1 .1.2, Send flag is 0x0 Composite metric is (2221056/307200), Route is Internal Vector metric: Minimum bandwidth is 1544 Kbit Total delay is 22000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 2

Use an offset list on R4 to change the composite metric on R2

The composite metric on R2 can be changed using an offset list on router R4. An offset list value of 20 on R4 increases the composite metric for path R2-R4 by 20 to R2. Hence, the path R2-R4 becomes a backup path to R2-R3. An offset list is the preferred method when:

  • They only want to influence a specific path that is advertised.

  • Additional routers are connected to the 10.1.3.0/24 subnet, and you don't want to affect the paths that the routers take.

  1. Configure an offset list on R4 that increases the delay (by 20) for each route that is used 10.1.3.x begins.

    R4 # configure terminal Enter configuration commands, one per line. End with CNTL / Z. R4 (config) # access-list 99 permit 10.1.3.0 0.0.0.255 R4 (config) # router eigrp 1 R4 (config-router) # offset-list 99 out 20 e0 / 0 R4 (config-router) # end R4 #
  2. In this output you can see that the offset list in the EIGRP topology table does not change anything for R4.

    The metric only changes when the route is announced.

    R4 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 281600 Routing Descriptor Blocks: 0.0.0.0 (Ethernet0 / 1), from Connected , Send flag is 0x0 Composite metric is (281600/ 0), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 1000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 0 10.1.2.3 (Ethernet0 / 0), from 10.1. 2.3, Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1
  3. On R2, make sure that the route through R3 (10.1.2.3) is again the only best path.

    R2 # show 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 - ISIS, L1 - ISIS level-1, L2 - ISIS level-2, * - candidate default U - per -user static route, o - ODR Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets D 10.1.3.0 [90/307200] via 10.1.2.3, 00:00:20, Ethernet0 C 10.1.2.0 is directly connected, Ethernet0 C 10.1.1.0 is directly connected, Serial0.101

    The EIGRP topology table reflects the increase in delay compared to R4 (10.1.2.4).

    R4 feasible distance (281600) + R4 offset list (20) = R4 reported distance (281620).

    Note: A cosmetic bug in version 12.0 (7) of the Cisco IOS software prevents the increased delay from being accurately reflected in the section of the output shown here.

    DDTSdescription
    CSCdp36097 (registered customers only)EIGRP: Offset list adds an incorrect delay value
    R2 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 307200 Routing Descriptor Blocks: 10.1.2.3 (Ethernet0), from 10.1.2.3 , Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1 10.1. 2.4 (Ethernet0), from 10.1.2.4, Send flag is 0x0 Composite metric is (307220 /281620), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1

Change the administrative distance at R2

It is also possible to change the path selection process by changing the administrative distance, on R2, of the route learned from R4. This method is less ideal than the others. For the reasons listed here, the routing loops potential can be increased:

  • Administrative distance is commonly used to determine the method by which a route was learned. If the setting is incorrect, the individual router cannot select a distributed route instead of the actual best path.

  • The administrative distance is not passed on to other routers. Routing protocols are based on the fact that all routers choose the same path if they set the same parameters. Changing parameters on a single router can create routing loops.

  1. Change the configuration of R2 so that with a routing update from R4 (10.1.2.4) for subnet 10.1.3.0/24 the administrative distance is increased to 91.

    91 is chosen because 1 is greater than the standard EIGRP administrative distance for internals (i.e. 90). The default administrative distance for EIGRP external connections (routes that are redistributed to EIGRP) is 170. The default values ​​of all routing protocols can be found in the document.

    R2 # configure terminal Enter configuration commands, one per line. End with CNTL / Z. R2 (config) # access-list 99 permit 10.1.3.0 0.0.0.255 R2 (config) # router eigrp 1 R2 (config-router) # distance 91 10.1.2.4 0.0.0.0 99 R2 (config-router) # end R2 #
  2. At this point you may need the command clear ip route for the changes to take effect.

    Note: Now there is only one path to 10.1.3.0/24 to R3 (10.1.2.3).

    R2 # show 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 - ISIS, L1 - ISIS level-1, L2 - ISIS level-2, * - candidate default U - per -user static route, o - ODR Gateway of last resort is not set 10.0.0.0/24 is subnetted, 3 subnets D 10.1.3.0 [90/307200] via 10.1.2.3, 00:05:28, Ethernet0 C 10.1.2.0 is directly connected, Ethernet0 C 10.1.1.0 is directly connected, Serial0.101

    Note: The EIGRP topology table has not changed.

    R2 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 307200 Routing Descriptor Blocks: 10.1.2.3 (Ethernet0), from 10.1.2.3 , Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1 10.1. 2.4 (Ethernet0), from 10.1.2.4, Send flag is 0x0 Composite metric is (307200/281600), Route is Internal Vector metric: Minimum bandwidth is 10000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1

Potential problems

Imagine R1 and R2 running Open Shortest Path First (OSPF) for the 11.0.0.0/8 network with an administrative distance of 110 to illustrate a potential problem that this method can cause if not careful can be used. Imagine R4 has a static route for 11.1.1.0/24 that points to R2 (10.1.2.2). R4 redistributes static routes on EIGRP so that some new routers under 10.1.3.0/24 can access 11.1.1.0/24.

R2 normally receives the external EIGRP route for 11.1.1.0/24 from R4 with an administrative distance of 170. Since this distance is greater than that of the OSPF route (110), it is not installed.

This output is an example of the distance command used above when configured incorrectly.

R2 # configure terminal Enter configuration commands, one per line. End with CNTL / Z. R2 (config) # access-list 99 permit 11.1.1.0 0.0.0.255 R2 (config) # router eigrp 1 R2 (config-router) # distance 91 10.1.2.4 0.0.0.0 99 R2 (config-router) # end R2 #

This configuration creates a routing loop between R2 and R4 for the subnet 11.1.1.0/24. R2 now prefers the route 11.1.1.0/24 announced by R4. This is because the administrative distance (91) is less than the administrative distance for the OSPF route (110).

Change the bandwidth at R2

The use of bandwidth to influence EIGRP paths should be avoided for two reasons:

  • A change in bandwidth can have effects beyond the EIGRP metrics. For example, Quality of Service (QoS) also takes into account the bandwidth of an interface.

  • EIGRP limits the use of 50 percent of the configured bandwidth. Reducing bandwidth can cause problems such as: B. the preservation of EIGRP neighbors with Hello packets, since the bandwidth is throttled back.

Changing the delay does not affect other protocols, nor does it cause EIGRP to throttle.

  1. Check the EIGRP topology table for R1 before making any changes.

    R1 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 2221056 Routing Descriptor Blocks: 10.1.1.2 (Serial0.201), from 10.1 .1.2, Send flag is 0x0 Composite metric is (2221056/307200), Route is Internal Vector metric: Minimum bandwidth is 1544 Kbit Total delay is 22000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 2
  2. Check the start values ​​for the Ethernet0 interface on R2.

    R2 # show interface ethernet0 Ethernet0 is up, line protocol is up Hardware is Lance, address is 0010.7b3c.6786 (bia 0010.7b3c.6786) Internet address is 10.1.2.2/24 MTU 1500 bytes, BW 10000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:01, output 00 : 00:02, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size / max / drops / flushes); Total output drops: 0 Queuing strategy: fifo Output queue: 0/40 (size / max) 5 minute input rate 0 bits / sec, 0 packets / sec 5 minute output rate 0 bits / sec, 0 packets / sec 1938 packets input, 165094 bytes, 0 no buffer Received 1919 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 1482 packets output, 124222 bytes, 0 underruns 0 output errors, 0 collisions, 18 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
  3. Reduce the bandwidth to see the effect on R1.

    R2 # configure terminal Enter configuration commands, one per line. End with CNTL / Z. R2 (config) # interface ethernet0 R2 (config-if) # bandwidth 5000 R2 (config-if) # end R2 #
  4. Confirm the change.

    R2 # show interface ethernet0 Ethernet0 is up, line protocol is up Hardware is Lance, address is 0010.7b3c.6786 (bia 0010.7b3c.6786) Internet address is 10.1.2.2/24 MTU 1500 bytes, BW 5000 Kbit, DLY 1000 usec, rely 255/255, load 1/255 Encapsulation ARPA, loopback not set, keepalive set (10 sec) ARP type: ARPA, ARP Timeout 04:00:00 Last input 00:00:02, output 00 : 00: 01, output hang never Last clearing of "show interface" counters never Input queue: 0/75/0/0 (size / max / drops / flushes); Total output drops: 0 Queuing strategy: fifo Output queue: 0/40 (size / max) 5 minute input rate 0 bits / sec, 0 packets / sec 5 minute output rate 0 bits / sec, 0 packets / sec 1995 packets input, 169919 bytes, 0 no buffer Received 1969 broadcasts, 0 runts, 0 giants, 0 throttles 0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort 0 input packets with dribble condition detected 1525 packets output, 127831 bytes, 0 underruns 0 output errors, 0 collisions, 18 interface resets 0 babbles, 0 late collision, 0 deferred 0 lost carrier, 0 no carrier 0 output buffer failures, 0 output buffers swapped out
  5. Confirm that this has also changed in the EIGRP topology table.

    R2 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 2 Successor (s), FD is 563200 Routing Descriptor Blocks: 10.1.2.4 (Ethernet0), from 10.1.2.4 , Send flag is 0x0 Composite metric is (563200/281600), Route is Internal Vector metric: Minimum bandwidth is 5000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1 10.1.2.3 (Ethernet0), from 10.1.2.3, Send flag is 0x0 Composite metric is (563200/281600), Route is Internal vector metric: Minimum bandwidth is 5000 Kbit Total delay is 2000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 1
  6. Review the effects on the EIGRP topology table for R1.

    R1 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 2221056 Routing Descriptor Blocks: 10.1.1.2 (Serial0.201), from 10.1 .1.2, Send flag is 0x0 Composite metric is (2221056/563200), Route is Internal Vector metric: Minimum bandwidth is 1544 Kbit Total delay is 22000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 2

    There is no change as the Frame Relay connection between R1 and R2 is still the lowest speed connection. You will only see a change if you reduce this bandwidth on the Ethernet0 interface for R2 to a value below 1544.

  7. Reduce the bandwidth of the Ethernet0 interface for R2 to 1000.

    R2 # configure terminal Enter configuration commands, one per line. End with CNTL / Z. R2 (config) # interface ethernet 0 R2 (config-if) # bandwidth 1000 R2 (config-if) # end R2 #
  8. Review the effects on the EIGRP topology table for R1.

    R1 # show ip eigrp topology 10.1.3.0 255.255.255.0 IP-EIGRP (AS 1): Topology entry for 10.1.3.0/24 State is Passive, Query origin flag is 1, 1 Successor (s), FD is 312320 Routing Descriptor Blocks: 10.1.1.2 (Serial0.201), from 10.1 .1.2, Send flag is 0x0 Composite metric is (3123200/2611200), Route is Internal Vector metric: Minimum bandwidth is 1000 Kbit Total delay is 22000 microseconds Reliability is 255/255 Load is 1/255 Minimum MTU is 1500 Hop count is 2

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