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2 Anatomy of an IP Packet IP packets consist of the data from upper layers plus an IP header. The IP header consists of the following:

3 Router What is an optimal route ? What is an optimal route ? Switch Routing Protocol

4 Path Determination Graphic

5 Routing Protocols Routing protocols includes the following: processes for sharing route information allows routers to communicate with other routers to update and maintain the routing tables Examples of routing protocols that support the IP routed protocol are: RIP, IGRP, OSPF, BGP, and EIGRP.

6 Routed Protocols Protocols used at the network layer that transfer data from one host to another across a router are called routed or routable protocols. The Internet Protocol (IP) and Novell's Internetwork Packet Exchange (IPX) are examples of routed protocols. Routers use routing protocols to exchange routing tables and share routing information. In other words, routing protocols enable routers to route routed protocols.

Dynamic Routing Protocols Function(s) of Dynamic Routing Protocols: – -Dynamically share information between routers. – -Automatically update routing table when topology changes. – -Determine best path to a destination.

Dynamic Routing Protocols The purpose of a dynamic routing protocol is to: – -Discover remote networks – -Maintaining up-to-date routing information – -Choosing the best path to destination networks – -Ability to find a new best path if the current path is no longer available

Dynamic Routing Protocols Components of a routing protocol – Algorithm In the case of a routing protocol algorithms are used for facilitating routing information and best path determination – Routing protocol messages These are messages for discovering neighbors and exchange of routing information

Static Routing Static routing algorithms are basically table mappings established by the network administrator before the beginning of routing. These mappings do not change unless the network administrator alters them. Algorithms that use static routes are simple to design and work well in environments where network traffic is relatively predictable and where network design is relatively simple. Because of this fact, static routing systems cannot react to network changes. Static routes remain in the routing table even if the specified gateway becomes unavailable. If the specified gateway becomes unavailable, you need to remove the static route from the routing table manually. However, static routes are removed from th e routing table if the specified interface goes down, and are reinstated when the interface comes back up.

Static Routing Advantages of static routing – -It can backup multiple interfaces/networks on a router – -Easy to configure – -No extra resources are needed – -More secure Disadvantages of static routing – -Network changes require manual reconfiguration – -Does not scale well in large topologies

12 Configuring Static Routes Static routes are table mappings established by the network administrator before the beginning of routing. These mappings do not change unless the network administrator alters them. A static route uses this format: route if_name dest_ip mask gateway_ip [distance] Example: hostname(config)# route outside [1]

13 Configuring Default Routes Default routes are used to route packets with destinations that do not match any of the other routes in the routing table. A default route is actually a special static route that uses this format: ip route [next-hop-address | outgoing interface] This is sometimes referred to as a “Quad-Zero” route. Example using next hop address: Router(config)#ip route Example using the exit interface: Router(config)#ip route s0/0

14 Verifying Static Route Configuration After static routes are configured it is important to verify that they are present in the routing table and that routing is working as expected. The command show running-config is used to view the active configuration in RAM to verify that the static route was entered correctly. The show ip route command is used to make sure that the static route is present in the routing table.

Classifying Routing Protocols Dynamic routing protocols are grouped according to characteristics. Examples include: – -RIP – -IGRP – -EIGRP – -OSPF – -IS-IS – -BGP Autonomous System is a group of routers under the control of a single authority.

Classifying Routing Protocols Types of routing protocols: – -Interior Gateway Protocols (IGP) – -Exterior Gateway Protocols (EGP)

Classifying Routing Protocols Interior Gateway Routing Protocols (IGP) – -Used for routing inside an autonomous system & used to route within the individual networks themselves. – -Examples: RIP, EIGRP, OSPF Exterior Routing Protocols (EGP) – -Used for routing between autonomous systems – -Example: BGPv4

18 Autonomous System AS 2000 AS 3000 IGP Interior Gateway Protocols are used for routing decisions within an Autonomous System. Exterior Gateway Protocols are used for routing between Autonomous Systems EGP AS 1000 An Autonomous System (AS) is a group of IP networks, which has a single and clearly defined external routing policy. Fig. 48 IGP and EGP (TI1332EU02TI_0004 The Network Layer, 67)

19 IGP Interior Gateway Protocol (IGP) Exterior Gateway Protocol (EGP) EGP Interior Gateway Protocol (IGP) AS 1000 AS 2000 AS 3000 Fig. 49 The use of IGP and EGP protocols (TI1332EU02TI_0004 The Network Layer, 67)

20 IGP and EGP An autonomous system is a network or set of networks under common administrative control, such as the cisco.com domain.

Classifying Routing Protocols IGP: Comparison of Distance Vector & Link State Routing Protocols – Distance vector –routes are advertised as vectors – of distance & direction. –incomplete view of network – topology. –Generally, periodic – updates. – Link state –complete view of network – topology is created. –updates are not – periodic. –

Classifying Routing Protocols

Classful routing protocols – Do NOT send subnet mask in routing updates Classless routing protocols – Do send subnet mask in – routing updates.

Classifying Routing Protocols Convergence is defined as when all routers’ routing tables are at a state of consistency

Routing Protocols Metrics Metric – A value used by a routing protocol to determine which routes are better than others.

Routing Protocols Metrics Metrics used in IP routing protocols – -Bandwidth – -Cost – -Delay – -Hop count – -Load – -Reliability

Routing Protocols Metrics The Metric Field in the Routing Table Metric used for each routing protocol – -RIP - hop count – -IGRP & EIGRP - Bandwidth (used by default), Delay (used by default), Load, Reliability – -IS-IS & OSPF – Cost, Bandwidth (Cisco’s implementation)

Routing Protocols Metrics Load balancing – This is the ability of a router to distribute packets among multiple same cost paths

Administrative Distance of a Route Purpose of a metric – It’s a calculated value used to determine the best path to a destination Purpose of Administrative Distance – It’s a numeric value that specifies the preference of a particular route

Administrative Distance of a Route Identifying the Administrative Distance (AD) in a routing table – It is the first number in the brackets in the routing table

Administrative Distance of a Route Dynamic Routing Protocols

Administrative Distance of a Route Directly connected routes – Have a default AD of 0 Static Routes – Administrative distance of a static route has a default value of 1

Administrative Distance of a Route Directly connected routes – -Immediately appear in the routing table as soon as the interface is configured

34 Categories of Routing Protocols Most routing algorithms can be classified into one of two categories: distance vector link-state The distance vector routing approach determines the direction (vector) and distance to any link in the internetwork. The link-state approach, also called shortest path first, recreates the exact topology of the entire internetwork.

35 Distance Vector Routing Concepts

36 2 Hops 1 Hop Destination Distance 1 2 Routing table contains the addresses of destinations and the distance of the way to this destination. Flow of routing information Flow of routing information Router BRouter CRouter ARouter D Distance Vector Routing (DVR)

37 Routing Tables Graphic

38 Distance Vector Topology Changes

39 Router Metric Components

40 Distance Vector Routing (DVR)

L L L L L L L L L L L L L L L L L L L L B B B B A A C C C C B B B B D D C C C C B B B B C C B B C C C C L L L L L L L L L L L L L L L L L L L L B B B B A A C C C C B B B B D D C C C C B B B B C C B B C C C C B B C C Distance Vector Routing (DVR) Fig. 53 Distribution of routing information with distance vector routing protocol (cont.) (TI1332EU02TI_0004 The Network Layer, 71)

Link State Routing protocol

43 Link State Concepts

44 Link State Topology Changes

45 LSP: „My links to R 2 and R 4 are up“ LSP: „My links to R 1 and R 3 are up, my link to R 4 is down.“ LSP: „My links to R 2 and R 4 are up.“ LSP: „My links to R 1 and R 3 are up. My link to R 2 is down.“ Router 1Router 4Router 2Router 3 SPF Routing Table Link State Routing (LSR) LSP....link state packet SPF... shortest path first

46 Link State Concerns

47 Router ARouter CRouter BRouter DRouter E B - 2 C - 1 B - 2 C - 1 A - 2 D - 4 A - 2 D - 4 A - 1 D - 2 E - 4 A - 1 D - 2 E - 4 C - 2 B - 4 E - 1 C - 2 B - 4 E - 1 C - 4 D - 1 C - 4 D - 1 Router ARouter BRouter CRouter DRouter E Link State Database A A CB D E AD EC B B DA EB C C ECB A D D Link State Routing (LSR)

48 Link State Routing Features Link-state algorithms are also known as Dijkstras algorithm or as SPF (shortest path first) algorithms. Link-state routing algorithms maintain a complex database of topology information. The distance vector algorithm are also known as Bellman-Ford algorithms. They have nonspecific information about distant networks and no knowledge of distant routers. A link-state routing algorithm maintains full knowledge of distant routers and how they interconnect. Link- state routing uses: Link-state advertisements (LSAs) A link-state advertisement (LSA) is a small packet of routing information that is sent between routers. Topological database A topological database is a collection of information gathered from LSAs. SPF algorithm The shortest path first (SPF) algorithm is a calculation performed on the database resulting in the SPF tree. Routing tables – A list of the known paths and interfaces.

49 Link State Routing

50 Comparing Routing Methods

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