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Chapter 10: Routing Protocols
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2. Chapter 10 Objectives
The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter:
1.9 Explain the basics of routing concepts and protocols
• Loopback interface
• Routing loops
• Routing tables
• Static vs. dynamic routes
• Default route
• Distance vector routing protocols
o RIP v2
• Hybrid routing protocols
o BGP
• Link state routing protocols
o OSPF
o IS-IS 2

3. Chapter 10 Objectives
The Following CompTIA Network+ Exam Objectives Are Covered in This Chapter:
• Interior vs. exterior gateway routing protocols
• Autonomous system numbers
• Route redistribution
• High availability
o VRRP
o Virtual IP
o HSRP
• Route aggregation
• Routing metrics
o Hop counts
o MTU, bandwidth
o Costs
o Latency
o Administrative distance
o SPB 3

4. Routing Protocol Basics
Routing protocols are critical to a network’s design. Dynamic routing protocols run only on routers that use them in order to discover networks and update their routing tables.
Using dynamic routing is easier on you, the system administrator, than the labor-intensive, manually achieved, static routing method is; but it’ll cost you in terms of router CPU processes and bandwidth on the network links.
A routing protocol defines the set of rules used by a router when it communicates routing information between its neighbor routers.
Autonomous System (AS) – collection of networks under a common administrative domain – all routers share the same routing table information are in the same AS 4

5. Routing Protocol Basics
The whole routing tree:
Static
Routing
Dynamic
Routing
EGP
Protocols:
BGP
IGP
Distance
Vector
Protocols:
RIPv1 & 2, IGRP
Link
State
Protocols:
OSPF, IS-IS
We’re going to look at the IGP branch and discover the workings of Distance Vector, Link State, and Hybrid routing protocols.
Hybrid
Protocols:
EIGRP/BGP 5

6. Administrative Distance
The administrative distance (AD) is used to rate the trustworthiness of routing information received on one router from its neighboring router.
If a router receives two updates listing the same remote network, the first thing the router checks is the AD. If one of the advertised routes has a lower AD than the other, the route with the lower AD is the one that will get placed in the routing table. 6

7. Classes of Routing Protocols
Distance vector
Find the best path to a remote network by judging distance. Each time a packet goes through a router we call it a hop. The route with fewest hops to the network is determined to be the best route.
Link State
Link State protocols create three separate tables. One of these tables keeps track of directly attached neighbors, one determines the topology of the entire internetwork, and one is used as the actual routing table. Link-state routers know more about the internetwork than any distance-vector routing protocol. 7

8. Classes of Routing Protocols
Hybrid
A hybrid protocol uses the best aspects of both distance vector and link state routing protocols. At this time, there’s EIGRP and BGP. EIGRP happens to be a Cisco proprietary protocol, meaning that it will only run on Cisco equipment. If you have a multi-vendor environment, this won’t work for you. 8

9. Distance Vector Routing Protocols
Each router has only the directly connected networks in each of their routing tables.
Each router sends its complete routing table, which includes the network number, exit interface, and hop count to the network, out to each active interface. 9

10. Distance Vector Routing Protocols
Routing table in each router keeps information about three important things:
The remote network number
The interface that the router will use to send packets to reach that particular network
The hop count, or metric, to the network 10

11. Routing Information Protocol (RIP)
RIP is a true distance-vector routing protocol.
It sends the complete routing table out to all active interfaces every 30 seconds.
RIP uses only one thing to determine the best way to a remote network—the hop count.
RIP has a maximum allowable hop count of 15 by default, a hop count of 16 would be deemed unreachable.
RIP = Classful
RIPv2 = Classless 11

12. Typical Classful Network
All interfaces use the same subnet mask.
All interfaces support the same number of devices.
Do all networks the networks in the diagram need the same number of devices (addresses)? 12

13. Classless network design
All interfaces can use a different subnet mask. Interfaces support a more efficient number of devices wasting less addresses.
In order to implement a VLSM design on your network, you need to have a routing protocol that sends subnet-mask information with the route updates.
RIPv2
EIGRP
OSPF 13

14. A discontiguous network
A discontiguous network has two or more subnetworks of a classful network connected together by different classful networks.
Discontiguous networks won’t work with RIPv1 or IGRP.
Discontiguous networks won’t work by default on RIPv2 or EIGRP (RIPv2 and EIGRP auto-summarize by default).
Discontiguous networks do work on OSPF networks by default because OSPF does not auto-summarize.
LAB_A EO
LAB_B – EO
Route aggregation 14

15. EIGRP
A great feature of EIGRP is that it’s simple to configure and turn on like a distance-vector protocol, but it keeps track of more information than distance vector does.
It creates and maintains additional tables instead of just one table as distance-vector routing protocols do.
These tables are called the neighbor table, topology table, and routing table.
Features of EIGRP: 15

16. Border Gateway Protocol (BGP)
IGPs: RIP, IGRP, EIGRP, OSPF
EGPs: BGP
BGP is used for IGPs to communicate ASs together
Because the Internet’s growth rate shows no signs of slowing, ISPs use BGP for its ability to make classless routing and summarization possible.
These capabilities help to keep routing tables smaller and more efficient at the ISP core.
BGP can also be used within an AS
Autonomous System 1
Autonomous System 2 16

17. RIP / OSPF Comparison
OSPF Features:
OSPF is the first link-state routing protocol that most people are introduced to, so it’s good to see how it compares to more traditional distance-vector protocols like RIPv2 and RIPv1. 17

18. OSPF Design Example Backbone Router Area 0 Area Border Router (ABR)
Autonomous System
Border Router (ASBR)
This shows a typical OSPF simple design.
Hierarchical fashion -
Note how each router connects to the backbone—called area 0, or the backbone area.
OSPF must have an area 0, and all other areas should connect to this area.
Routers that connect other areas to the backbone area within an AS are called Area Border Routers (ABRs).
Area 1
Area 2
Autonomous System 18

19. IS-IS Network Design Area 13 L2 AS 1200 L1/L2 L1/L2 Area 10 Area 12
IS-IS is an IGP used within an administrative domain or network.
IS-IS is a link-state routing protocol operating by reliably flooding topology information throughout a network of routers.
Each IS-IS router independently builds a picture of the network's topology similar to OSPF. 19

20. First Hop Redundancy Protocols (FHRP): HSRP – Cisco Proprietary
Figure 10.11
Fa0/1
Fa0/1
Fa0/0
Fa0/0
Virtual Router
Hot Standby Router Protocol
Virtual Router Redundancy Protocol
First Hop Redundancy Protocols (FHRP): HSRP – Cisco Proprietary
VRRP – Open Standard
IP:
Gateway:

21. Figure 10.12 10.0.0.1 10.0.0.2 Active Standby Fa0/1 Fa0/1 Fa0/0 Fa0/0
Virtual Router
Standby
IP:
Gateway:

22. Figure 10.13 10.0.0.2 10.0.0.1 Standby Active Fa0/1 Fa0/1 Fa0/0 Fa0/0
Virtual Router
Active
IP:
Gateway:

23. Figure 10.14 Hello? 10.0.0.1 10.0.0.2 Active Standby Fa0/1 Fa0/1
Virtual Router
Fa0/0
Hello?
Fa0/0
Active
Standby
IP:
Gateway:

24. IPv6 Routing Protocols RIPng EIGRPv6 OSPFv3
RIPng works the same as RIPv2.
RIPng is still a distance-vector protocol, has a max hop count of 15, and uses split horizon, poison reverse, and other loop avoidance mechanisms.
RIPng now uses UDP port 521.
EIGRPv6
EIGRPv6 works much the same as its IPv4 predecessor does—most of the features that EIGRP provided before EIGRPv6 will still be available.
OSPFv3
The foundation of OSPF remains the same—it is still a link-state routing protocol that divides an entire internetwork or autonomous system into areas, making a hierarchy. 24

25. Summary Summary Exam Essentials Section Written Labs Review Questions25