Static routing is inflexible and cannot adapt to network changes, while dynamic routing automatically adapts to topology changes. Dynamic routing protocols include distance vector protocols like RIP that use hop counts as metrics and link-state protocols like OSPF that use link costs. These protocols exchange routing information to build and maintain routing tables and converge on consistent views of the network topology.

2. Static and Dynamic Routing
 Static Routing is a simplistic approach.
 Shortcomings
 Cumbersome to configure.
 Cannot adapt to addition of new links or nodes.
 Cannot adapt to link or node failures.
 Cannot easily handle multiple paths to a
destination.
 Does not scale to large networks.
 Solution is to use Dynamic Routing.

3. Desirable Characteristics of
Dynamic Routing
 Automatically detect and adapt to topology
changes.
 Provide optimal routing.
 Scalability.
 Robustness.
 Simplicity.
 Rapid convergence.
 Some control of routing choices.

4. Convergence – why do I
care?
 Convergence is when all the routers have the
same routing information.
 When a network is not converged there is network
downtime.
 Packets don’t get to where they are supposed to
go.
○ Black holes (packets “disappear”)
○ Routing Loops (packets go back and fore between the
same devices)
 Occurs when there is a change in status of
router or the links.

5. Dynamic Routing Protocols
Dynamic
Routing protocol
Interior Gateway
Protocols
IGPs
Distance
vector
RIPv1
RIPv2
Hybrid
EIGRP
Link-state
IS-IS OSPF
Exterior Gateway
protocols
EGPs
BGP

6. Interior Gateway Protocols
 IGP is a type of protocol used for
exchanging routing information between
gateways within an autonomous system.
 This routing information can then be used to route network-
layer protocols like IP.

7. RIP

8. RIP
 RIP was one of the first true Distance Vector routing
protocols.
 RIP uses the Bellman-Ford Distance Vector algorithm.
 Listen to neighbouring routes
 Install all routes in routing table
○ Lowest hop count wins
 Advertise all routes in table
○ Very simple, very stupid
 Only metric is hop count
 Network is max 16 hops (not large enough).
 periodic routing updates (every 30 seconds)

9. RIP (cont.)
 RIP supports IP and IPX routing.
 RIP utilizes UDP port 520
 Administrative distance of 120.
 RIP has a maximum hop count of 15
hops.
 RIPv1 is classful.
 RIPv1 does not support authentication

10. RIPv2
 RIPv2 is classless routing
 RIPv2 routing updates are sent as
multicast address of 224.0.0.9
 RIPv2 supports authentication

11. EIGRP
 Enhanced Interior Gateway Routing Protocol
 EIGRP is a Cisco-proprietary Hybrid routing
protocol
 EIGRP uses Diffusing Update Algorithm (DUAL)
 EIGRP will form neighbor relationships with
adjacent routers in the same Autonomous System
(AS).
 Support unicasts, multicasts (address 224.0.0.10)
 Reliable Transport Protocol (RTP)
 Updates are sent when a change occurs
 EIGRP Hellos are sent every 5 sec, 60 sec
 Hold timer is three times the Hello timer

12. EIGRP (cont.)
 EIGRP is a classless protocol, and thus supports
VLSMs
 EIGRP supports IP, IPX, and Appletalk routing
 Administrative Distance of 90, 170
 Maximum hop-count of 224, default hop-count is set
to 100.
 EIGRP Metric = 256*(10000000/Bandwidth + Delay)
 Eigrp supports three other parameters to calculate its
metric: Reliability, Load, and MTU.
 EIGRP, builds three separate tables
 Neighbor table
 Topology table
 Routing table

13. EIGRP (cont.)
 An EIGRP route can exist in one of two states, in the
topology table:
 Active state
 Passive State
 EIGRP employs five packet types-
• multicastHello packets
• unicast or multicastUpdate packets
• multicastQuery packets
• unicastReply packets
• unicast
Acknowledgement
packets

14. OSPF
 Open Shortest Path First
 “Open” means it is public domain
 Uses “Shortest Path First” algorithm – sometimes
called “the Dijkstra algorithm”
 IETF Working Group formed in 1988 to design an IGP
for IP
 OSPF v1 published in 1989 – RFC1131
 OSPF v2 published in 1991 – RFC1247
 Developments continued through the 90s and today
 OSPFv3 includes extensions to support IPv6
 Network is Divided into Areas
 Backbone area (area 0)
 Off backbone area (area 1-65,535)
 Special routers (autonomous system boundary routers)
or backbone routers responsible to dissipate
information about other AS into the current system.

15. OSPF (cont.)
 Carried in data field of IP packet
 Protocol value is 89
 No hop-counts limits
 AD value is 110
 Support classless network
 VLSM/CIDR
 Unique id for every router
 OSPF traffic is multicast either to address 224.0.0.5 or 224.0.0.6
 Metric = cost
 The OSPF process builds and maintains three separate tables
 Neighbor table
 Topology table
 Routing table
 Hello packets (10 seconds, 30 sec)
 Dead Interval (40 sec, 120 sec)

16. OSPF (cont.)
 Advertise LSA to maintain updates
•The Router LSA is generated by each router for each area it is
located. In the link-state ID you will find the originating router’s ID.LSA Type 1: Router LSA
• Network LSAs are generated by the DR. The link-state ID will
be the router ID of the DR.LSA Type 2: Network LSA
• The summary LSA is created by the ABR and flooded into
other areas.LSA Type 3: Summary LSA
•Other routers need to know where to find the ASBR. This is why the
ABR will generate a summary ASBR LSA which will include the router
ID of the ASBR in the link-state ID field.
LSA Type 4: Summary ASBR
LSA
• also known as autonomous system external LSA:
The external LSAs are generated by the ASBR.
LSA Type 5: Autonomous system
external LSA
LSA Type 6: Multicast OSPF LSA
•also known as not-so-stubby-area (NSSA) LSA: As you can see area 1
is a NSSA (not-so-stubby-area) which doesn’t allow external LSAs (type
5). To overcome this issue we are generating type 7 LSAs instead.
LSA Type 7: Not-so-stubby area
LSA
LSA Type 8: External attribute
LSA for BGP