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Routing & EIGRP

Routing & EIGRP. CCNA 3.0. Enhanced Interior Gateway Routing Protocol (EIGRP). Really just an enhanced version of IGRP A Cisco proprietary routing protocol Called a hybrid protocol, but really just an advanced distance vector protocol. Fast convergence Variable length subnet masks

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Routing & EIGRP

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  1. Routing & EIGRP CCNA 3.0

  2. Enhanced Interior Gateway Routing Protocol (EIGRP) • Really just an enhanced version of IGRP • A Cisco proprietary routing protocol • Called a hybrid protocol, but really just an advanced distance vector protocol. • Fast convergence • Variable length subnet masks • Partial updates - only when the metric for a route changes (bounded updates) • Multiple network layer support - IP, IPX, and AppleTalk • A router running EIGRP stores all its neighbor’s routing tables so that it can quickly adapt or alternate routes.

  3. Features of EIGRP • Classless Routing Protocol (VLSM, CIDR) • Faster convergence times and improved scalability • Multiprotocol support: TCP/IP, IPX/SPX, Appletalk • There is no IPX/SPX or Appletalk in CCNA or CCNP • Rapid Convergence and Better handling of routing loops – (DUAL) • Efficient Use of Bandwidth • Partial, bounded updates: Incremental updates only to the routers that need them. • Minimal bandwidth consumption: Hello packets and by default uses no more that 50% of link’s bandwidth EIGRP packets. • PDM (Protocol Dependent Module) • Keeps EIGRP modular • Different PDMs can be added to EIGRP as new routed protocols are enhanced or developed: IPv4, IPv6, IPX, and AppleTalk

  4. IGRP & EIGRP They work together and routes are redistributed automatically RTB(config)# router igrp 2446 RTB(config-router)#network 192.168.1.0 RTB(config)#router eigrp 2446 RTB(config-router)# network 10.1.1.0 RTB(config-router)# network 172.16.1.0

  5. IGRP & EIGRP

  6. Metric calculation: IGRP/EIGRP metric = [K1 * bandwidth + ((K2 * bandwidth) / (256 * load)) + (K3 * delay)] * [K5/(reliability + K4)] • (with the following default constant values): • Constant Value • K1 1 • K2 0 • K3 1 • K4 0 • K5 0 Notes • k2 metric effects LOAD • k4 and k5 effects RELIABILITY

  7. Metric Calculation metric = [K1 * bandwidth + ((K2 * bandwidth) / (256 * load)) + (K3 * delay)] * [K5/(reliability + K4)] When K2, K4 and K5 are 0, these portions of the equation is not factored in to the metric. Thus, with the default constant values, K1=1 and K3=1, the metric equation boils down to this: • metric = [(1 * bandwidth)+ (1 * delay)] • metric =bandwidth + delay Actually: metric =slowestbandwidth + sum of alldelays

  8. Metric Calculation 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 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.

  9. 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! Use show interface command to view the metrics used on a specific interface that is routing EIGRP.

  10. Metric Calculation – show interfaces 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)

  11. IGRP & EIGRP • The routers in the EIGRP network will convert the 24-bit IGRP metric that IGRP uses to its 32-bit metric • EIGRP Metric = IGRP Metric x 256 (32 bit vs. 24 bit)

  12. EIGRP Terminology Has these for EACH routed protocol

  13. Improvements from IGRP • Neighbor discovery & recovery • Use small “hello” packets to estab. adjacencies – sent every 5 seconds • Dynamically learn routes that way • Reliable Transport Protocol (RTP) • A transport layer protocol (Layer 4) that guarantees delivery order • EIGRP is protocol independent, so has its own guarantee (compare to TCP)

  14. Improvements from IGRP • Dual finite-state machine • An algorithm that EIGRP uses to calculate routes • Tracks all routes advertised by neighbors and uses a composite metric of each route to compare them • Protocol-dependent modules • Each module is responsible for all functions related to its specific routed protocol • In other words, there is an IP PDM, an IPX PDM, an AppleTalk PDM, etc.

  15. EIGRP Neighbor Table • This table is the basis for all EIGRP routing updates & convergence • Has IP info about neighbor routers • Smooth Round Trip Timer (SRTT)The average time it takes to send and receive packets from a neighbor. • Queue count The number of packets waiting in queue to be sent.

  16. EIGRP Topology Table RouterB#show ip eigrp topology IP-EIGRP Topology Table for process 44 Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply, r - Reply status P 206.202.17.0/24, 1 successors, FD is 2195456 via 206.202.16.1 (2195456/2169856), Ethernet0 P 206.202.18.0/24, 2 successors, FD is 2198016 via 192.168.0.2 (2198016/284160), Serial0 via 206.202.16.1 (2198016/2172416), Ethernet0 Each EIGRP router maintains a topology table for each configured network protocol. This table includes the current routes (successors) and back-up routes (feasible successors). P = Passive (good), A = Active (not ready, DUAL running) EIGRP uses its topology table to store all the information it needs to calculate a set of distances and vectors to all reachable destinations. Info for the destination route: routing protocol, feasible distance of the route, the route cost

  17. Few Terms RD=5 RD=5 10 FD=15 FD=15 10 14 15 15 20 Coming soon: RD = Reported Distance FD = Feasible Distance FD=20 6 RD=6 Successor – Current Route • A successor is a route selected as the primary route to use to reach a destination. • Successors are the entries kept in the routing table. Feasible Successor - A backup route • These routes are selected at the same time the successors are identified, but they are kept in the topology table. • Multiple feasible successors for a destination can be retained in the topology table.

  18. Few Terms RD=5 RD=5 10 FD=15 FD=15 10 14 15 15 20 FD=20 6 RD=6 Feasible distance (FD) is the minimum distance (metric) along a path to a destination network. (“This Router’s Distance”) Reported distance (RD) is the distance (metric) towards a destination as advertised by an upstream neighbor. (“The Neighbor Router’s Distance”)

  19. RouterX’s FD = 30 to 172.30.1.0/24 (Sent as RD to RouterA) RouterX RouterY’s FD = 21 to 172.30.1.0/24 (Sent as RD to RouterA) Best Route RouterY FD = 31 172.30.1.0 is 31 via RouterY RouterZ’s FD =220 to 172.30.1.0/24 (Sent as RD to RouterA) RouterZ The Feasible Distance to a network is sent to other routers, as this router’s Reported Distance.

  20. Feasible Successor: RD= 30, FC: RD30 < FD31 RouterX (Current) Successor: RD= 21 RouterY FD = 31 172.30.1.0 is 31 via RouterY NOT a Feasible Successor: RD = 220, FC not met: RD220 > FD31 RouterZ A neighbor meets the feasible condition (FC) if the reported distance by the neighbor is smaller than the current feasible distance (FD) of this router. • A distance-vector routing protocol not allowing possible paths with loops paths. • "If a neighbors metric is less than mine, then I know the neighbor doesn't have a loop going through me." A feasible successor (FS) is a neighbor whose reported distance (RD) is less than the current feasible distance (FD). • Feasible successor is one who meets the feasible condition (FC).

  21. DUAL – Diffusing Update Algorithm The centerpiece of EIGRP is DUAL fsm (finite state machine), the EIGRP route-calculation engine. DUAL selects alternate routes quickly by using the information in the EIGRP neighbor and topology table. If a link goes down, DUAL looks for a feasible successor in its topology table. Feasible successors provide the next lowest-cost path without introducing routing loops. Selects a best loop-free path to a destination, the next hop being known as the successor. All other routers to the same destination, that also meet the feasible condition, meaning they are also loop-free, become feasible successors, or back-up routes. Router# debug eigrp fsm

  22. EIGRP Packet Types

  23. Looking for a New Route RtrD RtrB Queries Replies RtrE RtrA X RtrF RtrC RtrG • If there are no Feasible Successors, the router must ask neighbors for help in hope of finding a new, loop-free path to the destination. • Neighbor routers are compelled to reply to this query. • If a neighbor has a route, it will reply with information about the successor(s). • If not, the neighbor notifies the sender that it doesn’t have a route to the destination either.

  24. EIGRP Routing Table This command shows only EIGRP routing table entries Note that the default administrative distance is 90 with EIGRP internal routes • Contains routes installed by DUAL FSM as the best loop-free paths • Can maintain up to 4 routes per destination • Maintains a separate routing table for each protocol Routing table has the primary route to a destination – this primary route is ALSO in the topology table

  25. Basic EIGRP Configuration EIGRP Commands Router(config)# router eigrpAS • AS must be the same on all routers. Router(config-router)# networknetwork-number Interface Commands Router(config-if)# bandwidthkilobits • Serial links should reflect actual link bandwidth instead of the default of 1544 kbps – or the network may not be able to converge • Bandwidth should be set because a less desirable route could be chosen as the best path if the bandwidth setting is higher than the actual bandwidth of the link Router(config-if)# eigrp log-neighbor-changes • This command enables the logging of neighbor adjacency changes to monitor the stability of the routing system and to help detect problems.

  26. Configuring EIGRP Summarization EIGRP Commands Router(config-router)# no auto-summary • Like RIP and IGRP, EIGRP automatically summarizes as major network boundaries. • This command turns off automatic summarization, useful for discontiguous networks (see RIPv2 example). Interface Commands Router(config-if)# ip summary-addresseigrp autonomous-system-number ip-address mask [administrative-distance] • Summarizes addresses being advertised out of this interface. • Administrative distance for EIGRP Summary Routes is 5, but can be modified (optional).

  27. Configuring EIGRP Summarization EIGRP Commands Router(config-router)# no auto-summary • Like RIP and IGRP, EIGRP automatically summarizes as major network boundaries. • This command turns off automatic summarization, useful for discontiguous networks Interface Commands Router(config-if)# ip summary-addresseigrp autonomous-system-number ip-address mask [administrative-distance] • Summarizes addresses being advertised out of this interface. • Administrative distance for EIGRP Summary Routes is 5, but can be modified (optional).

  28. Configuring a Default Route Method 1: Quad-Zero Static Route Gateway Router ip route 0.0.0.0 0.0.0.0 serial0 ! router eigrp 100 redistribute static <text omitted> Method 2: ip default-network command Gateway Router router igrp 24 <text omitted> network 207.21.20.0 ip default-network 207.21.20.0 ip route 0.0.0.0 0.0.0.0 207.21.20.1

  29. Troubleshooting IGRP commands when network is unreachable • show ip route to see if the network has been installed in the routing table • show ip protocols to verify that IGRP is indeed advertising that network. • show running-configuration to check the network statements.

  30. Troubleshooting • Use show commands to monitor normal router behavior • Use debug for finding specific problems

  31. Routing & EIGRP CCNA 3.0

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