* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Routing Protocol vs. Routed Protocol
Survey
Document related concepts
Distributed firewall wikipedia , lookup
Piggybacking (Internet access) wikipedia , lookup
Backpressure routing wikipedia , lookup
Deep packet inspection wikipedia , lookup
Network tap wikipedia , lookup
List of wireless community networks by region wikipedia , lookup
Wake-on-LAN wikipedia , lookup
IEEE 802.1aq wikipedia , lookup
Cracking of wireless networks wikipedia , lookup
Zero-configuration networking wikipedia , lookup
Internet protocol suite wikipedia , lookup
Multiprotocol Label Switching wikipedia , lookup
Computer network wikipedia , lookup
Airborne Networking wikipedia , lookup
Recursive InterNetwork Architecture (RINA) wikipedia , lookup
Transcript
Chapter 5 IP Routing Routing Protocol vs. Routed Protocol Topics • Review – – – – Internetworking Path determination Router IP Address • Routed and Routing Protocols – Network protocols • Routed • Routing – Interior Protocols vs. Exterior Protocols • Routing Protocol Activity 2 Review Router and IP Address Internetworking 4 Path determination • Path determination is the process that the router uses to choose the next hop in the path for the packet to travel to its destination based on the link bandwidth, hop, delay ... 5 Router • A router is a type of internetworking device that passes data packets between networks, based on Layer 3 addresses. • A router has the ability to make intelligent decisions regarding the best path for delivery of data on the network. 6 IP addresses • IP addresses are implemented in software, and refer to the network on which a device is located. • IP addressing scheme, according to their geographical location, department, or floor within a building. • Because they are implemented in software, IP addresses are fairly easy to change. 7 Router and Bridge 8 Router connections • Routers connect two or more networks, each of which must have a unique network number in order for routing to be successful. • The unique network number is incorporated into the IP address that is assigned to each device attached to that network. 9 Router Interface 10 Router function 11 Router function (cont.1) Strips off the data link header, carried by the frame. (The data link header contains the MAC addresses of the source and destination.) 12 Router function (cont.2) Examines the network layer address to determine the destination network. 13 Router function (cont.3) Consults its routing tables to determine which of its interfaces it will use to send the data, in order for it to reach its destination network. 14 Router function (cont.4) Send the data out interface B1, the router would encapsulate the data in the appropriate data link frame. 15 Router Interface example • Interface is a router’s attachment to a network, it may also be referred to as a port. In IP routing. • Each interface must have a separate, unique 16 network address. ROUTED AND ROUTING PROTOCOLS Network protocols • In order to allow two host communicate together through internetwork, they need a same network protocol. • Protocols are like languages. • IP is a network layer protocol. 18 Network protocol operation 19 Routed protocol • Protocols that provide support for the network layer are called routed or routable protocols. • IP is a network layer protocol, and because of that, it can be routed over an internetwork. 20 Protocol addressing variations 21 Three important routed protocols • TCP/IP: 04 bytes – Class A: 1 byte network + 3 bytes host – Class B: 2 bytes network + 2 bytes host – Class C: 3 bytes network + 1 byte host • IPX/SPX: 10 bytes – 4 bytes network + 6 bytes host • AppleTalk: 03 bytes – 2 bytes network + 1 byte host 22 Non-routable protocol • Non-routable protocols are protocols that do not support Layer 3. • The most common of these non-routable protocols is NetBEUI. • NetBEUI is a small, fast, and efficient protocol that is limited to running on one segment. 23 Addressing of a routable protocol 24 Routing table 131.108.1.0 E0 131.108.2.0 E1 131.108.3.0 E2 25 Multi-protocol routing 26 • Classification #1: Static and Dynamic Static routes: – The network administrator manually enter the routing information in the router. • Dynamic routes: – Routers can learn the information from each other on the fly. – Using routing protocol to update routing information. – RIP, IGRP, EIGRP, OSPF … 27 Static routes 28 Dynamic routes 29 Static vs. dynamic routes • Static routes: – For hiding parts of an internetwork. – To test a particular link in a network. – For maintaining routing tables whenever there is only one path to a destination network. • Dynamic routes: – – – – Maintenance of routing table. Timely distribution of information in the form of routing updates. Relies on routing protocol to share knowledge. Routers can adjust to changing network conditions. 30 Routing protocol • Routing protocols determine the paths that routed protocols follow to their destinations. • Routing protocols enable routers that are connected to create a map, internally, of other routers in the network or on the Internet. 31 Routed vs. Routing protocol 32 Classification #2: IGP and EGP • Dynamic routes. • Interior Gateway Protocols (RIP, IGRP, EIGRP, OSPF): – Be used within an autonomous system, a network of routers under one administration, like a corporate network, a school district's network, or a government agency's network. • Exterior Gateway Protocols (EGP, BGP): – Be used to route packets between autonomous systems. 33 IGP vs. EGP IGP EGP 34 Classification #3: DVP and LSP • Distance-Vector Protocols (RIP, IGRP): – – – – View network topology from neighbor’s perspective. Add distance vectors from router to router. Frequent, periodic updates. Pass copy of routing tables to neighbor routers. • Link State Protocols (OSPF): – – – – Gets common view of entire network topology. Calculates the shortest path to other routers. Event-triggered updates. Passes link state routing updates to other routers. 35 Distance vector routing 36 Link state routing 37 Part II Distance Vector Routing 39 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—3-39 • • Distance Vector Routing Protocols Dynamic routing protocols help the network administrator overcome the time-consuming and exacting process of configuring and maintaining static routes. Examples of Distance Vector routing protocols: Routing Information Protocol (RIP) –RFC 1058. –Hop count is used as the metric for path selection. –If the hop count for a network is greater than 15, RIP cannot supply a route to that network. –Routing updates are broadcast or multicast every 30 seconds, by default. Interior Gateway Routing Protocol (IGRP) –proprietary protocol developed by Cisco. –Bandwidth, delay, load and reliability are used to create a composite metric. –Routing updates are broadcast every 90 seconds, by default. –IGRP is the predecessor of EIGRP and is now obsolete. Enhanced Interior Gateway Routing Protocol (EIGRP) –Cisco proprietary distance vector routing protocol. –It can perform unequal cost load balancing. –It uses Diffusing Update Algorithm (DUAL) to calculate the shortest path. –There are no periodic updates as with RIP and IGRP. Routing updates are sent only when there is a change in the topology. Distance Vector Routing Protocols • The Meaning of Distance Vector: –A router using distance vector routing protocols knows 2 things: Distance to final destination The distance or how far it is to the destination network Vector, or direction, traffic should be directed The direction or interface in which packets should be forwarded For example, in the figure, R1 knows that the distance to reach network 172.16.3.0/24 is 1 hop and that the direction is out the interface S0/0/0 toward R2. Distance Vector Routing Protocols • Characteristics of Distance Vector routing protocols: Periodic updates • Periodic Updates sent at regular intervals (30 seconds for RIP). Even if the topology has not changed in several days, Neighbors The router is only aware of the network addresses of its own interfaces and the remote network addresses it can reach through its neighbors. It has no broader knowledge of the network topology Broadcast updates Broadcast Updates are sent to 255.255.255.255. Some distance vector routing protocols use multicast addresses instead of broadcast addresses. Entire routing table is included with routing update Entire Routing Table Updates are sent, with some exceptions to be discussed later, periodically to all neighbors. Neighbors receiving these updates must process the entire update to find pertinent information and discard the rest. Some distance vector routing protocols like EIGRP do not send periodic routing table updates. Distance Vector Routing Protocols Routing Protocol Algorithm: –The algorithm is used to calculate the best paths and then send that information to the neighbors. –Different routing protocols use different algorithms to install routes in the routing table, send updates to neighbors, and make path determination decisions. Distance Vector Routing Protocols Routing Protocol Characteristics –Criteria used to compare routing protocols includes Time to convergence Time to convergence defines how quickly the routers in the network topology share routing information and reach a state of consistent knowledge. The faster the convergence, the more preferable the protocol. Scalability Scalability defines how large a network can become based on the routing protocol that is deployed. The larger the network is, the more scalable the routing protocol needs to be. Resource usage Resource usage includes the requirements of a routing protocol such as memory space, CPU utilization, and link bandwidth utilization. Higher resource requirements necessitate more powerful hardware to support the routing protocol operation Classless (Use of VLSM) or Classful Classless routing protocols include the subnet mask in the updates. This feature supports the use of Variable Length Subnet Masking (VLSM) and better route summarization. Implementation & maintenance Implementation and maintenance describes the level of knowledge that is required for a network administrator to implement and maintain the network based on the routing protocol deployed. Distance Vector Routing Protocols • Routers pass periodic copies of their routing table to neighboring routers and accumulate distance vectors. 45 Sources of Information and Discovering Routes • Routers discover the best path to destinations from each neighbor. 46 Selecting the Best Route with Metrics 47 Maintaining Routing Information • Updates proceed step by step from router to router. 48 Inconsistent Routing Entries • Each node maintains the distance from itself to each possible destination network. 49 Inconsistent Routing Entries (Cont.) • Slow convergence produces inconsistent routing. 50 Inconsistent Routing Entries (Cont.) • Router C concludes that the best path to network 10.4.0.0 is through router B. 51 Inconsistent Routing Entries (Cont.) • Router A updates its table to reflect the new but erroneous hop count. 52 Count to Infinity • The hop count for network 10.4.0.0 counts to infinity. 53 Routing Loops • Packets for network 10.4.0.0 bounce (loop) between routers B and C. 54 Routing Loops • Routing loops can eliminate –Defining a maximum metric to prevent count to infinity –Holddown timers –Split horizon –Route poisoning or poison reverse –Triggered updates • Note: The IP protocol has its own mechanism to prevent the possibility of a packet traversing the network endlessly. IP has a Time-to-Live (TTL) field and its value is decremented by 1 at each router. –If the TTL is zero, the router drops the packet. Defining a Maximum • A limit is set on the number of hops to prevent infinite loops. 56 Triggered Updates • The router sends updates when a change in its routing table occurs. 57 Route Poisoning • Routers advertise the distance of routes that have gone down to infinity. 58 Split Horizon • It is never useful to send information about a route back in the direction from which the original information came. 59 Poison Reverse • Poison reverse overrides split horizon. 60 Holddown Timers • The router keeps an entry for the “possibly down state” in the network, allowing time for other routers to recompute for this topology change. 61 Link-State Routing 62 © 2004 Cisco Systems, Inc. All rights reserved. ICND v2.2—3-62 Link-State Routing • Link state routing protocols – -Also known as shortest path first algorithms -These protocols built around Dijkstra’s SPF OSPF will be discussed in Chapter 11, and IS-IS will be discussed in CCNP. Link-State Routing Protocols • After initial flood of LSAs, link-state routers pass small event-triggered link64 state updates to all other routers. Link-State Routing • Dikjstra’s algorithm also known as the shortest path first (SPF) algorithm –This algorithm accumulates costs along each path, from source to destination. Link-State Routing: Step 1 – Learn about directly connected Networks • Link This is an interface on a router • Link state This is the information about the state of the links Link-State Routing: step 2 - Sending Hello Packets to Neighbors • Link state routing protocols use a hello protocol Purpose of a hello protocol: -To discover neighbors (that use the same link state routing protocol) on its link Link-State Routing: step 2 - Sending Hello Packets to Neighbors • Connected interfaces that are using the same link state routing protocols will exchange hello packets. • Once routers learn it has neighbors they form an adjacency – 2 adjacent neighbors will exchange hello packets – These packets will serve as a keep alive function Link-State Routing: step 3 - Building the Link State Packet (LSP) • Contents of LSP: – State of each directly connected link – Includes information about neighbors such as neighbor ID, link type, & bandwidth. • A simplified version of the LSPs from R1 is: –1. R1; Ethernet network 10.1.0.0/16; Cost 2 –2. R1 -> R2; Serial point-to-point network; 10.2.0.0/16; Cost 20 –3. R1 -> R3; Serial point-to-point network; 10.3.0.0/16; Cost 5 –4. R1 -> R4; Serial point-to-point network; 10.4.0.0/16; Cost 20 Link-State Routing: step 4 - Flooding LSPs to Neighbors • Once LSP are created they are forwarded out to neighbors. –Each router floods its link-state information to all other link-state routers in the routing area. –Whenever a router receives an LSP from a neighboring router, it immediately sends that LSP out all other interfaces except the interface that received the LSP. –This process creates a flooding effect of LSPs from all routers throughout the routing area. Link-State Routing: step 4 - Flooding LSPs to Neighbors • LSPs are sent out under the following conditions – Initial router start up or routing process – When there is a change in topology • including a link going down or coming up, or a neighbor adjacency being established or broken Link-State Routing: step 5 - Constructing a link state data base • Routers use a database to construct a topology map of the network –After each router has propagated its own LSPs using the link-state flooding process, each router will then have an LSP from every link-state router in the routing area. –These LSPs are stored in the linkstate database. –Each router in the routing area can now use the SPF algorithm to construct the SPF trees that you saw earlier. Link-State Routing: step 5 - Constructing a link state data base router R1 has learned the link-state information for each router in its routing area. With a complete link-state database, R1 can now use the database and the shortest path first (SPF) algorithm to calculate the preferred path or shortest path to each network. Drawbacks to Link-State Routing Protocols • Initial discovery may cause flooding. • Link-state routing is memory- and processorintensive. 74 How Routing Information Is Maintained 75 Link-State Routing Protocol Algorithms 76 Link-State Routing Protocols Advantages of a Link-State Routing Protocol Routing protocol Builds Topological map Router can independently determine the shortest path to every network. Convergence Event driven routing updates Use of LSP Distance vector No No Slow Generally No No Link State Yes Yes Fast Generally Yes Yes Link-State Routing Protocols • • There are several advantages of link-state routing protocols compared to distance vector routing protocols. Builds a Topological Map • • • Fast Convergence • • • When receiving a Link-state Packet (LSP), link-state routing protocols immediately flood the LSP out all interfaces except for the interface from which the LSP was received. A router using a distance vector routing protocol needs to process each routing update and update its routing table before flooding them out other interfaces, even with triggered updates. Event-driven Updates • • • Link-state routing protocols create a topological map, or SPF tree of the network topology. • Using the SPF tree, each router can independently determine the shortest path to every network. Distance vector routing protocols do not have a topological map of the network. • Routers implementing a distance vector routing protocol only have a list of networks, which includes the cost (distance) and next-hop routers (direction) to those networks. After the initial flooding of LSPs, link-state routing protocols only send out an LSP when there is a change in the topology. The LSP contains only the information regarding the affected link. Unlike some distance vector routing protocols, link-state routing protocols do not send periodic updates. Hierarchical Design • Link-state routing protocols such as OSPF and IS-IS use the concept of areas. Multiple areas create a hierarchical design to networks, allowing for better route aggregation (summarization) and the isolation of routing issues within an area. Link-State Routing Protocols Requirements for using a link state routing protocol • Memory requirements – Typically link state routing protocols use more memory • Processing Requirements – More CPU processing is required of link state routing protocols • Bandwidth Requirements – Initial startup of link state routing protocols can consume lots of bandwidth – This should only occur during initial startup of routers, but can also be an issue on unstable networks. Link-State Routing Protocols • Modern link-state routing protocols are designed to minimize the effects on memory, CPU, and bandwidth. • • • • The use and configuration of multiple areas can reduce the size of the link-state databases. Multiple areas can also limit the amount of link-state information flooding in a routing domain and send LSPs only to those routers that need them. For example, when there is a change in the topology, only those routers in the affected area receive the LSP and run the SPF algorithm. This can help isolate an unstable link to a specific area in the routing domain. In the figure, If a network in Area 51 goes down, the LSP with the information about this downed link is only flooded to other routers in that area. • Routers in other areas will learn that this route is down, but this will be done with a type of link-state packet that does not cause them to rerun their SPF algorithm. Note: Multiple areas with OSPF and IS-IS are discussed in CCNP Link-State Routing Protocols • 2 link state routing protocols used for routing IP -Open Shortest Path First (OSPF) -Intermediate System-Intermediate System (IS-IS) Routing Protocol RIP • • • • • • • • Most popular. Interior Gateway Protocol. Distance Vector Protocol. Only metric is number of hops. Maximum number of hops is 15. Updates every 30 seconds. Doesn’t always select fastest path. Generates lots of network traffic. 83 IGRP and EIGRP • • • • Cisco proprietary. Interior Gateway Protocol. Distance Vector Protocol. Metric is compose of bandwidth, load, delay and reliability. • Maximum number of hops is 255. • Updates every 90 seconds. • EIGRP is an advanced version of IGRP, that is hybrid routing protocol. 84 OSPF • • • • Open Shortest Path First. Interior Gateway Protocol. Link State Protocol. Metric is compose of cost, speed, traffic, reliability, and security. • Event-triggered updates. 85 End Chapter V