Routing protocols Part III

1. Routing protocolsPart III ET4187/ET5187 Advanced Telecommunication Network

2. Enhanced Interior Gateway Routing Protocol(EIGRP)

3. 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.

4. 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.

5. 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

6. 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

7. 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)

8. EIGRP Terminology

9. 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)

10. 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.

11. 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

12. 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 countThe number of packets waiting in queue to be sent.

13. 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.

14. Few Terms RD=5 RD=5 10 FD=15 FD=15 10 14 15 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.

15. 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”)

16. 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.

17. 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).

18. 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.

19. 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

20. EIGRP Packet Types

21. Data Structures

22. 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.

23. 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