Routing Protocols Enhanced IGRP (EIGRP) Characteristics

Transcription

1 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Objectives EIGRP Routing Protocols and Concepts Chapter 9 Examine the basic EIGRP configuration commands and identify their purposes. Calculate the composite metric used by EIGRP. Describe the concepts and operation of DUAL. Describe the uses of additional configuration commands in EIGRP. ITE PC v4.0 Chapter Routing Protocols Enhanced IGRP (EIGRP) Characteristics Advanced distance vector routing protocol Classless - supports VLSM and CIDR Cisco proprietary Scalable, Fast network convergence Uses composite metric based on: Bandwidth (used by default) Delay (used by default) Reliability (optional) Load (optional) 3 Supports authentication 4 EIGRP Message Format EIGRP Reliable Transport Protocol (RTP) Used instead of TCP. EIGRP messages are carried in unicast or multicast IP packets. EIGRP packet header - contains AS number Type/Length/Value Field - data portion of EIGRP message Protocol-dependent modules (PDM) provide a capability for routing several different protocols including IP, IPX, and AppleTalk 5 RTP sends multicast or unicast packets, depending on the message type Uses multicast address EIGRP has 5 packet types Hello packets to discover and establish adjacencies with neighbour EIGRP routers Update and Acknowledgement (ACK) packets. Query and Reply packets 6

2 Hello Protocol EIGRP Updates Hello packets are sent periodically to - Discover directly connected neighbors and form adjacencies. - Confirm the link is still up Hello interval is 5 seconds (multicasts) or 60 seconds (unicast) by default Hold time is three times the hello interval This is how long EIGRP will wait to receive an Hello before considering the neighbor down Hello and Hold time can be configured by the EIGRP sends updates only when there is a change in the route status EIGRP updates are partial and bounded Partial only the route information that has changed is sent Bounded only those devices that are impacted by the change are notified EIGRP s use of partial bounded updates, and non-use of broadcasts, minimizes the use of bandwidth administrator (fine tuning) 7 8 EIGRP Tables EIGRP AD Routing table The best route to each network based on Administrative Distance and Metric Neighbor table Details of EIGRP neighbor adjacencies Topology table Details of all routes All Successor routes All Feasible Successor (backup) routes FD, RD 9 Administrative Distance (AD) Defined as the trustworthiness of the source route EIGRP default administrative distances Summary routes = 5 Internal routes = 90 Imported routes = Autonomous System EIGRP Basic Configuration This is a collection of networks under the control of a single authority (RFC 1930) AS Numbers are assigned by IANA Entities needing AS numbers: ISPs Internet backbone providers Large institutions 11 R(config)# router eigrp autonomous-system EIGRP autonomous system number actually functions as a process ID A process ID represents an instance of the routing protocol running on a router Process ID is a 16-bit number: 1 to All routers in an EIGRP domain must use the same process ID (or AS number) We usually just use the number 1 Note that using 0 is an error 12

3 The network statement R(config-router)# network network-address This statement has two functions: - Determines which interfaces will send and receive EIGRP hellos and updates - Determines which networks or subnets will be advertised to other EIGRP neighbors R1(config)# network R2(config)# network The network statement with Wildcard Mask R(config-router)# network net-address [wildcard-mask] This option is used when you want to configure EIGRP to advertise specific subnets Verifying EIGRP EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received To view neighbor table and verify that EIGRP has established adjacencies with neighbors is show ip eigrp neighbors R3(config)# network network R2#show ip eigrp neighbors IP-EIGRP neighbors for process 1 H Address Interface Hold Uptime SRTT RTO Q Seq (sec) (ms) Cnt Num Ser0/0/ :00: Ser0/0/ :00: R2# 16 Examining the Routing Table The Null0 Summary Route show ip route command is used to verify EIGRP EIGRP routes are denoted by the letter D R2# show ip route Gateway of last resort is not set /30 is subnetted, 1 subnets C is directly connected, Loopback /16 is variably subnetted, 4 subnets, 3 masks D /16 is a summary, 00:07:15, Null0 D /24 [90/ ] via , 00:07:15, Serial0/0 C /24 is directly connected, FastEthernet0/0 C /30 is directly connected, Serial0/0/0 D /24 [90/ ] via , 00:07:31, Serial0/ /24 is variably subnetted, 3 subnets, 2 masks D /24 is a summary, 00:05:29, Null0 D /30 [90/ ] via , 00:05:29, Serial0/1 C /30 is directly connected, Serial0/0/1 17 R2# By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist One or more subnets exists that was learned via EIGRP Automatic summarization is enabled With EIGRP, auto-summary is enabled by default 18

4 Disabling Automatic Summarization The default auto-summary command permits EIGRP to automatically summarize at major network boundaries The no auto-summary command is used to disable automatic summarization This causes all EIGRP neighbors to send updates that will not be automatically summarized This will cause changes to appear in both -routing tables -topology tables 19 Default auto-summary on all routers network network R3# show ip route Gateway of last resort is not set D /16 [90/ ] via , 01:09:36, Serial0/0 C /24 is directly connected, FastEthernet0/ /24 is variably subnetted, 3 subnets, 2 masks D /24 is a summary, 01:09:35, Null0 C /30 is directly connected, Serial0/0/0 C /30 is directly connected, Serial0/0/1 R3# 20 no auto-summary on all routers network network no auto-summary R3# show ip route Gateway of last resort is not set /16 is variably subnetted, 4 subnets, 3 masks D /16 [90/ ] via , 00:00:01, Serial0/0 D /24 [90/ ] via , 00:00:01, Serial0/0 D /24 [90/ ] via , 00:00:01, Serial0/1 D /30 [90/ ] via , 00:00:01, Serial0/1 [90/ ] via , 00:00:01, Serial0/0 C /24 is directly connected, FastEthernet0/ /24 is variably subnetted, 3 subnets, 2 masks D /24 [90/ ] via , 00:00:01, Serial0/0 C /30 is directly connected, Serial0/0/0 C /30 is directly connected, Serial0/0/1 21 R3# EIGRP Metric Calculation EIGRP calculates a composite metric based on Bandwidth (minimum interface b/w on path) Delay (sum of link delays on path) Reliability Load using the formula: metric = [K1*bandwidth +(K2*bandwidth/(256-load) ) + K3*delay] * [K5/(reliability + K4)]. 22 EIGRP Metric Calculation The bandwidth statement The default K values are: K1 and K3 = 1 K2, K4 and K5 = 0 This means that the default metric calculation is: metric = bandwidth + delay The K values can be configured to include Reliability and Load in the calculation if required by the admin. 23 Bandwidth is a default static value (in kilobits) which depends on the type of interface On serial interfaces it defaults to 1544 kilobits (this is a standard T1 line) If the actual bandwidth is different, the calculated metric will not be correct The admin can configure the bandwidth value on a serial interface with the statement: R(config-if)# bandwidth kilobits Note that the bandwidth statement does not change the link s physical bandwidth 24

5 int fa0/0 ip address int lo1 ip address description To ISP int s0/0/0 ip address bandwidth 64 int s0/0/1 ip address clock rate bandwidth 1024 R2 config Diffusing Update Algorithm (DUAL) DUAL is the algorithm used by EIGRP Determines loop-free routes Provides for fast convergence by keeping backup routes, where possible Minimum bandwidth usage with bounded updates Design is based on a Finite State Machine DUAL Concepts Successor The best route to a destination. Added to the routing table Feasible distance (FD) The lowest calculated metric along a path to a destination network Feasible Successor This a loop free backup route to same destination as the Successor route, i.e. a backup route DUAL Concepts Reported distance (RD) The metric that a router reports to a neighbor about its own cost to that network Feasibility Condition Met when a neighbor s RD is less than the local router s FD to the same destination network Choosing the best route After a router has received all updates from directly connected neighbors, DUAL can calculate its routes to each network 1 - metric is calculated for each route 2 - the route with lowest metric is designated the successor & is offered to the routing table 3 - feasible successor is found Criteria for feasible successor: it must have lower reported distance to the destination than the installed route s feasible distance Feasible routes are maintained in the topology table 29 R2 has routes to /24 via R3 and R1 R3 is the successor route. Why? Does the route via R1 qualify as a feasible successor? 30

6 R2# show ip eigrp topology IP-EIGRP Topology Table for AS 1 EIGRP Topology Table dissected Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status P /24, 1 successors, FD is via Connected, FastEthernet0/0 P /30, 1 successors, FD is via Connected, Serial0/0/1 P /16, 1 successors, FD is via Summary (28160/0), Null0 P /24, 1 successors, FD is via Summary ( /0), Null0 P /24, 1 successors, FD is via ( /28160), Serial0/0/1 via ( / ), Serial0/0/0 P /30, 1 successors, FD is via Connected, Serial0/0/0 P /24, 1 successors, FD is via ( /28160), Serial0/0/0 P /30, 1 successors, FD is via ( / ), Serial0/0/ No Feasible Successor? A feasible successor may not be present because the feasibility condition may not be met In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance If the successor route goes down, the route will change from Passive mode and be placed in Active mode. A new route will have to be found This will involve querying neighbors This will take time 33 Manual Summarization Manual summarization can include supernets Reason: EIGRP is a classless routing protocol & includes subnet masks in updates Statement used to configure manual summarization R(config-if)# ip summary-address eigrp as net-addr subnet-mask Route / 24 Route /24 Route /24 Summary /22 34 Configuring a summary route in EIGRP EIGRP Default Routes interface Serial0/0/0 ip address ip summary-address eigrp clock rate interface Serial0/0/1 bandwidth 1024 ip address ip summary-address eigrp quad zero static default route -Can be used with any currently supported routing protocol -Is usually configured on a router that is connected to a network outside the EIGRP domain EIGRP & the Quad zero static default route Requires the use of the redistribute static command to disseminate default route in EIGRP updates 36

7 Redistribute static route from R2 to R1 R2# show run no auto-summary redistribute static ip route Loopback1 R1# show ip route Gateway of last resort is to network Fine-Tuning EIGRP EIGRP bandwidth utilization -By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information -The command to change the percentage of bandwidth used by EIGRP is R(config-if)# ip bandwidth-percent eigrp as percent /30 is subnetted, 2 subnets C is directly connected, Serial0/0/1 D [90/ ] via , 00:12:05, Serial0/0/ /16 is variably subnetted, 3 subnets, 2 masks C /24 is directly connected, FastEthernet0/0 D /24 [90/ ] via , 00:12:05, Serial0/0/1 C /30 is directly connected, Serial0/0/0 D*EX /0 [170/ ] via , 00:02:14, Serial0/0/1 D /22 [90/ ] via , 00:12:05, Serial0/0/ Configuring Hello Intervals and Hold Times Hello intervals and hold times are configurable on a per-interface basis Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval R(config-if)# ip hello-interval eigrp as seconds R(config-if)# ip hold-time eigrp as seconds 39 Lab 9.6.1: Basic EIGRP Configuration This lab can be done on Packet Tracer 4.11 by downloading the activity, with the following limitations: The WAN cable between R1 and R3 is connected the wrong way round when compared to the Hands-on Lab. Delete and reconnect it. When no auto-summary is configured, the config needs to be saved and the router reloaded before the Null0 routes disappear from the routing table. The statement to manually summarize routes is accepted, but it does not appear to have any effect. Redistribute static statement is not implemented. 40 Lab 9.6.1: Basic EIGRP Configuration 41