Routing protocols Part III ET4187/ET5187 Advanced Telecommunication Network

Enhanced Interior Gateway Routing Protocol (EIGRP)

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 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.

EIGRP Concepts Every EIGRP router maintains a topology table for each configured network protocol. All learned routes to a destination are maintained in the topology table.

Features of EIGRP Classless Routing Protocol (VLSM, CIDR) Faster convergence times and improved scalability Multiprotocol support: TCP/IP, IPX/SPX, Appletalk 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

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

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)

EIGRP Terminology Term Definition Neighbor table Topology table Lists adjacent routers (like adjacency DB in OSPF Topology table Each router has one for each network protocol routed Routing table Chooses routes from topology table – maintains one for each network protocol Successor Route selected as the primary route to use to reach a destination Feasible successor A backup route to above – multiple feasible successors for a destination can be kept in the topology table

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 that guarantees delivery order EIGRP is protocol independent, so has its own guarantee (compare to TCP)

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.

EIGRP Technologies Neighbor discovery and recovery Reliable Transport Protocol DUAL finite-state machine algorithm Protocol-dependent modules By forming adjacencies, EIGRP routers: Dynamically learn of new routes that join their network Identify routers that become either unreachable or inoperable Rediscover routers that had previously been unreachable

EIGRP Neighbor Table This table is the basis for all EIGRP routing updates & convergence Has info about the 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.

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.

Few Terms RD=5 RD=5 FD=15 FD=15 FD=20 RD=6 Successor – Current Route 10 FD=15 FD=15 10 14 15 20 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.

Few Terms RD=5 RD=5 FD=15 FD=15 FD=20 RD=6 10 FD=15 FD=15 10 14 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”)

RouterX’s FD = 30 to 172.30.1.0/24 (Sent as RD to RouterA) 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.

Feasible successor is one who meets the feasible condition (FC). 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).

Select Routes If a link goes down, DUAL looks for an alternative route path, or feasible successor, in the topology table. If a feasible successor is not found, the route is flagged as Active, or unusable at present. Query packets are sent to neighboring routers requesting topology information. DUAL uses this information to recalculate successor and feasible successor routes to the destination.

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. 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

EIGRP Packet Types Packet Definition Hello - multicast Discovers, verifies, rediscovers neighbor routers Acknowledgement (unicast) Indicates receipt of an EIGRP during a reliable packet Update When a router discovers a new neighbor or a topology change Query Needing specific info from a neighbor Reply Response to a query

Data Structures

X Looking for a New Route Queries Replies 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.

EIGRP Routing Table 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