1. Routing protocols Part 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
RTB(config)#router eigrp 2446
RTB(config-router)# network
RTB(config-router)# network

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 /30
MTU 1500 bytes, BW 1544 Kbit, DLY 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 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

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 count The 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 /24, 1 successors, FD is
via ( / ), Ethernet0
P /24, 2 successors, FD is
via ( /284160), Serial0
via ( / ), 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 FD=15 FD=15 FD=20 RD=6 Successor – Current Route10
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.

15. Few Terms RD=5 RD=5 FD=15 FD=15 FD=20 RD=610
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”)

16. RouterX’s FD = 30 to 172.30.1.0/24 (Sent as RD to RouterA)
RouterY’s FD = 21 to /24 (Sent as RD to RouterA)
Best Route
RouterY
FD = is 31 via RouterY
RouterZ’s FD =220 to /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 is one who meets the feasible condition (FC).
Feasible Successor: RD= 30, FC: RD30 < FD31
RouterX
(Current) Successor: RD= 21
RouterY
FD = 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 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

21. Data Structures

22. 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.

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