CCNA Routing Fundamentals - EIGRP, OSPF and RIP

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CCNA: ROUTING
By Sushmil Garde

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ROUTING
 Router IOS
 Boot Process
 Command Line Interface (CLI)
 Routing protocols and static routing

ROUTER IOS
 Carries Network Protocols and Functions
 Connects high speed traffic between network devices
 Adds security to network access
 Provides scalability for growth
 Supplies reliability

ROUTER BOOTUP PROCESS
 Three stage process
 Perform POST (Power On Self Test) and load Bootstrap Program
 Locate and load the Cisco IOS software
 Bootstrap Program performs this task
 By default IOS is stored in flash memory
 Locate Startup Configuration file or enter in Setup Mode.
 Bootstrap searches for startup config (present in NVRAM)
 Or else goes in Setup Mode.

ROUTERS- MODES OF OPERATION
 User Mode
 Privileged Mode
 Global Configuration Mode

EDITING COMMANDS FOR NETWORK GEEKS
Commands Explanation
Ctrl+A Moves the cursor to the begining of the line
Ctrl+E Moves the cursor to the end of the line
Esc+B Moves back one Word
Esc+F Moves forward one Word
Ctrl+R Redisplays a line
Ctrl+U Erases a line
Ctrl+W Erases a word
Ctrl+Z Ends configuration mode
TAB Finishes command for you

EDITING COMMANDS FOR NETWORK GEEKS
Commands Explanation
Ctrl+P Shows Last entered command
Ctrl+N Shows Previous commands entered
Show history Show last 10 commands entered by default
Show terminal Shows terminal configurations and history buffer size
Terminal history size Changes buffer size (max 256)

BASIC CONFIGURATION AND IMPORTANT
COMMANDS
 Configuring Hostname:
Router(config)# hostname <NAME>
 Configuring Banner:
Router(config)#banner motd ^c <TYPE THE BANNER>
 Configuring Password:
Router(config)#enable password
Router(config)#enable secret
 Interface configuration
Router(config)#
 …and many more

ROUTING
 WHAT DOES A ROUTER KNOW?
 Router knows about all the networks it can reach
 All paths to reach all networks
 Best path to reach all network
 Neighbor router

ROUTING
 IMPORTANT STATEMENTS:
 For end to end communication, it is not enough to have only forwarding
path, but having reverse path is also important.
 If you can reach one host on a network that does not mean you can reach all
hosts on that network.
 Initially router knows only about its directly connected neighbors, hence
can only communicate with them.
 Router must know the route to reach the destination network

STATIC vs DYNAMIC
 There are two ways to provide routes to the router
 Static Routing
 Provide the route manually
 Not very helpful in larger network
 Better when there is a need to provide a specific route
 Dynamic Routing
 Configuring Routing Protocols on routers
 Very useful in larger network
 Calculates the best path automatically

LEARNING A ROUTE THROUGH MULTIPLE
ROUTING PROTOCOLS
PROBLEM:
If a route is learnt from static entry/any routing protocol and same is learnt from
other routing protocol and both paths are different, then which path to prefer?
SOLUTION:
Administrative Distance (AD)
This is a value associated with each routing protocol and also with static route.
Lower the AD value better the path.
So, the router will prefer the path dictated by the one with LOWER AD value.

ONE ROUTING PROTOCOL MULTIPLE PATHS
PROBLEM:
If there is only one Routing Protocol running on the router and it receives two
different routes to reach same network, then which one to prefer?
SOLUTION:
Metric:
This is a value associated with the path. Every routing protocol has a way to
calculate its own metric. Lower the Metric Better the path and hence preferred.

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DYNAMIC ROUTING- ROUTING PROTOCOLS
 Routing protocols can be categorized as
 Interior Gateway Protocol
 Exterior Gateway Protocol
 Routing Protocols can also be categorized as
 Classful Protocols
 Classless Protocols
 …and also as
 Link state Routing
 Distance Vector Routing
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DYNAMIC ROUTING- ROUTING PROTOCOLS
 Interior Gateway Protocols (IGP):
– RIPv1 (CF/DV)
– RIPv2 (CL/DV)
– IGRP (CF/DV)
– IBGP (CL/DV)
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– EIGRP (CL/Ad. DV)
– OSPF (CL/LS)
– ISIS (CL/LS)
 Exterior Gateway Protocols (EGP):
– EBGP (CL/DV)
ROUTING PROTOCOL

CLASSFUL ROUTING
 Classful Routing Protocols do not send subnet mask with
its route information
 Classful Routing automatically summarizes the mask at
Classful boundaries.
 May lead to Sub-optimal paths.
 Examples of Classful Routing Protocols:
• RIP Version 1 (RIPv1)
• IGRP
16

CLASSLESS ROUTING
 Classless Routing Protocol send subnet mask with IP route
information
 Classless routing protocols support variable-length subnet
masking (VLSM).
 Examples of classless routing protocols:
i. RIP Version 2 (RIPv2)
ii. EIGRP
iii. OSPF
iv. IS-IS
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DISTANCE VECTOR ROUTING PROTOCOL
 These are the protocols in which…
 Updates are sent periodically (every 30/90 seconds)
 Entire Routing Table is sent as an update
 Updates are broadcasted
 Updates are sent to directly connected neighbors only and not to
the entire group
 Routers don’t have end-to-end visibility of the entire network,
Directly connected neighbors are the worlds
 Convergence is slow.
 RIP, IGRP and BGP are DISTANCE VECTOR Routing Protocols
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ROUTING INFORMATION PROTOCOL
 Used for smaller networks
 Metric: Hop Count
 Maximum Hop Count: 15
 Administrative Distance: 120
 Load Balancing: over equal metric path (4 by default)
 RIP versions: RIPv1 and RIPv2
 RIPv1 sends updates on Broadcast address
 RIPv2 sends updates on Multicast address 224.0.0.9
 Encrypted Authentication between 2 RIPv2 routers
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RIP TIMERS
• Update Timer: (default: 30 sec): Indicates how often the router will send out a routing
update
• Invalid Timer: (default: 180 sec): Indicates how long the route will remain in the
routing table before it gets invalid, if no new updates are received
• Hold-Down Timer: (default: 180 sec): Indicate how long RIP will suppress the route
that it has placed in HOLD state.
– HOLD state:
• Invalid timer has expired.
• Update received for a router marking that route with Metric 16 (unreachable)
• An update received from a router, with a higher metric than what is currently in
the routing table. (to prevent loops)
• Flush Timer: (default: 240 sec): Indicates how long a route can stay in the routing table
before its been flushed, if updates are not received
20

LINK STATE ROUTING PROTOCOL
 These are the protocols in which
 Updates are triggered and not periodic
 Updates are incremental, entire routing table is not sent as a part of
routing update
 Updates are sent as a multicast and not as broadcast
 Convergence is fast as updates are triggered
 Routers have end to end visibility of entire network through
topology table.
 OSPF and ISIS are Link State Routing Protocols
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ADVANCED DISTANCE VECTOR ROUTING PROTOCOL
 Combination of both Distance vector and Link State routing
protocols
 Best features of both are used in this
 Best feature of D.V Simple Configuration
 Best feature of L.S triggered updates, convergence is fast
etc.
 Used only in EIGRP
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ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL
(EIGRP)
 Classless Routing Protocol
 Cisco Proprietary Protocol
 Advanced Distance Vector Protocol
 Uses DUAL (Diffusion Update Algorithm) to determine Best Path to
reach destinations
 Neighbors are formed with only directly connected routers
 Mostly the EIGRP traffic is sent on Multicast Address 224.0.0.10
 Updates are incremental and triggered
 Summarization can be done on any router interface manually
 Administrative Distance:
 Internal EIGRP : Routes originating within local AS- 90
 External EIGRP: Routes coming from outside AS- 170
 Summary EIGRP: 5
23

EIGRP
 Maintains 3 tables
 Neighbor Table: List of all neighbor routers
 Topology Table: List of all routes in the AS
 Routing Table: Best routes to reach all networks
 Load Balancing:
 Load balancing on unequal metric path is possible.
 Default value: 4; Max Value: 6
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EIGRP OPERATION
 When routers are up, they exchange Multicast Hellos.
 Neighbor relation is formed after this exchange. Only directly
connected routers can become neighbors
 Topology table will be exchanged, till every router reaches converged
state
 After every router reaches converged state…
 No more exchange of Topology table, only updates will be sent after
modification in the network topology.
 EIGRP DUAL is run to find the best path to reach all networks
 Multicast echoes are exchanged to check the connectivity (Keep
Alive)
25

EIGRP METRIC
 EIGRP is called COMPOSIT METRIC
 Bandwidth (K1) and Delay of the line (K3) is used by default to
calculate the distance Metric
 Reliability (K4/K5), MTU and Load (K2) are the other 3 parameters
that can be considered
 By default:
EIGRP METRIC=
10000000
𝐵𝑊 (𝐾𝑏𝑝𝑠)
+ delay * 256
26

EIGRP- EXTRA
 EIGRP elects Next Best path at the same time, when it elects BEST
PATH
 Best Path is called as SUCCESSOR
 Next Best Path is called as FEASIBLE SUCCESSOR
 RULES:
 For a path to be considered as a feasible successor, its Advertised
Distance should be less than current Feasible Distance.
 For a path to be considered as a valid path, its AD should be less
than 2 times current FD
27

DUAL
28
(a)
(1)
(2)
(1)
(1)
(1)
(2)
A
D
EC
B
FOR ROUTER C:
FD AD Topology
Via B 3 1 Successor
Via D 4 2 Feasible Successor
Via E 4 3
AD: Advertised Distance
FD: Feasible Distance

OPEN SHORTEST PATH FIRST- OSPF
 Linked State Routing Protocol
 Metric: COST
 Higher the Bandwidth Lower the Cost, Lower the Cost Better the Path.
 𝐶𝑂𝑆𝑇 =
108
𝐵𝑊
 Determine the Best Path to reach all networks: Dijkstra Shortest Path
Algorithm
 AD Value: 110
 Sends Mask as a part of updates hence supports VLSM
 Updates are triggered
 Load Balancing on EQUAL costs path
 Multicast Address: 224.0.0.5 and 224.0.0.6
 Every OSPF router carries the visibility of the entire network with the help of
Link State Database
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TABLES
 Neighbor Table
 Topology Table- Link State Database
 EIGRP and other DV protocols: Info that just have been passed on
by neighbors
 They know the roadmap to their entire AREA
 Routing Table
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THE PROBLEM
 OSPF is a highly scalable protocol and can scale up to 1000s of routers.
 Has end to end visibility every router knows about all routes to reach
entire networks
 Updates are triggered after each Network Modification. This includes
addition/deletion of the route from routing table
 High Process Utilization
 High Bandwidth Utilization
 High Memory Utilization
 Solution: Summarization
31

CONCEPT OF AREA
32
AREA 2AREA 1
AREA 0-
BACKBONEInternal
Router
Area Border
Router (ABR)
Autonomous
System Boundary
Router (ASBR)

CONCEPT OF AREA
 All areas must connect to Area 0- One interface of ABR must
be connected to AREA 0
 All routers in an area have the same Topology Table
 Purpose: Localizing updates within a area
 Automatic Summarization is done at the ABR/ASBR only
 Hierarchical design is required
33

OSPF ROUTER ID
 In OSPF neighbors are identified by their RIDs
 RID is the highest IP of LOOPBACK interface.
 In absence of LOOPBACK interface, it’s the IP of highest ACTIVE
INTERFACE when router starts
 RID is also Hardcoded in the configuration using router id command-
Highest Preference
34

OSPF NEIGHBOR RELATIONSHIP
 Determining own Router ID
 Hardcoded
 Loopback
 Physical
 Add interfaces to Link State Database dictated by Network Command
 Send Hello on those interfaces
 This is DOWN state: Sending Hello but still waiting to hear back
 Receives Hello
 Goes in INIT state
 Checks: Hello/Dead timer, Authentication password, Area ID, Net mask 
must be identical
 Other parameters: DR/BDR IP address, Router ID and Router Priority
 Reaches TWO WAY state.
35

OSPF NEIGHBOR RELATIONSHIP
 Determines Master-Slave Relationship
 Determines who will send the routing first
 This is an EX_START ST
 Higher priority  Masters
 Master sends Database Description Packets (DBD) like cliff notes
 Slave sends DBDs
 DBDs are Acknowledged and Reviewed
 Router Goes in LOADING state
 First slave reviews the DBD and asks for missing info through LINK STATE REQUEST
to Master
 Master sends response in terms of LINK STATE UPDATES
 Master sends LSR and Slave responds back with LSU
 Neighbors are Synchronized
 This is the FULL STATE
 Now, Dijkstra’s SPF algorithm is applied to chose the Best Path and put it in the
routing table
 Keep Alive are sent
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DR/BDR
37
 DR/BDR listen on 224.0.0.6
 DROTHERS listen on 224.0.0.5
 DR/BDR is only for shared segments
 DR/BDR election is based on Router
Priority (Default: 1)
 If Router Priority is equal then the
Tie Breaker is the Router ID
 DROTHERS DO NOT need to
exchange their entire Routing info
with each other. Send it to only DR
and BDR
 Hence can stuck in TWO WAY state

OSPF PACKETS
 Hello:
 Sent every 10/30 sec
 Contains- Router ID, DR/BDR, Subnet Mask, Neighbors, Hello/Dead Intervals,
Auth Password, Router Priority, Area ID
 Neighbor relationship formation and keep alive
 Data-Base Description:
 Cliff notes sent in Ex-start state
 Link State Request:
 Sent in Loading state for requesting detailed information about a Network
 Link State Update:
 Response LSR
 Contain Multiple LSA
 Link State Advertisement:
 Response of each sub request
 Link State Acknowledgement:
 Reliability Mechanism
 OSPF itself is a Reliability Protocol
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LSA TYPES
 LSA 1 (Router LSA): contains a list of links local to the
router and generated by all the routers in the area
 LSA 2 (Network LSA): Generated by DR, contains list of all
routers attached to it
 LSA 3 (Network Summary LSA): Generated by ABRs; Used
for inter-area communication
 LSA 4 (ASBR Summary LSA): Route to reach ASBR
 LSA 5 (External LSA): Generated by ASBR and contains
routes to reach destinations outside local AS.
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THANK YOU!

CCNA Routing Fundamentals - EIGRP, OSPF and RIP

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