IRT0030 ANDMESIDE LOENG 5. Indrek Rokk

Transcription

1 IRT0030 ANDMESIDE LOENG 5 Indrek Rokk

2 2 Harjutus Aadress 2001:db8:aaaa:fc:50a5:8a35:a5bb:66e1/64 Küsimused Interface ID Subnet prefix Site prefix ISP prefix ISP prefix kahendkoodis Registry number Registry number kahendkoodis

3 3 Harjutus - vastus Aadress 2001:db8:aaaa:fc:50a5:8a35:a5bb:66e1/64 Küsimused Interface ID Subnet prefix Site prefix ISP prefix - 50a5:8a35:a5bb:66e1-00fc - aaaa - 1:0db8 ISP prefix kahendkoodis Registry number Registry number kahendkoodis

4 4 Routing versus Forwarding Routing = building maps and giving directions Forwarding = moving packets between interfaces according to the directions

5 5 IP Routing finding the path Path derived from information received from a routing protocol Several alternative paths may exist best path stored in forwarding table Decisions are updated periodically or as topology changes (event driven) Decisions are based on: topology, policies and metrics (hop count, filtering, delay, bandwidth, etc.)

6 6 IP Forwarding Router makes decision on which interface a packet is sent to Forwarding table populated by routing process Forwarding decisions: destination address class of service (fair queuing, precedence, others) local requirements (packet filtering) Can be aided by special hardware

7 7 Routing Tables Feed the Forwarding Table

8 8 RIBs and FIBs FIB is the Forwarding Table It contains destinations and the interfaces to get to those destinations Used by the router to figure out where to send the packet Careful! Some people call this a route! RIB is the Routing Table It contains a list of all the destinations and the various next hops used to get to those destinations and lots of other information too! One destination can have lots of possible next-hops only the best next-hop goes into the FIB

9 Router as a Computer 9

10 10 Routing Table Structure Routing Table is stored in ram and contains information about: Directly connected networks - this occurs when a device is connected to another router interface Remotely connected networks - this is a network that is not directly connected to a particular router Detailed information about the networks include source of information, network address & subnet mask, and IP address of next-hop router

11 11 Routing Table Structure Dynamic routing protocols -Used to add remote networks to a routing table -Are used to discover networks -Are used to update and maintain routing tables Automatic network discovery -Routers are able discover new networks by sharing routing table information

12 12 Routing Table Structure Maintaining routing tables -Dynamic routing protocols are used to share routing information with other router & to maintain and up date their own routing table. IP routing protocols. Example of routing protocols include: -RIP -EIGRP -OSPF

13 13 Routing Table Structure 3 principles regarding routing tables: Every router makes its decisions alone, based on the information it has in its routing table. Different routing table may contain different information A routing table can tell how to get to a destination but not how to get back

14 14 Effects of the 3 Routing Table Principles -Packets are forwarded through the network from one router to another, on a hop by hop basis. -Packets can take path X to a destination but return via path Y (Asymmetric routing).

15 Router Paths and Packet Switching A Metric is a numerical value used by routing protocols help determine the best path to a destination The smaller the metric value the better the path 2 types of metrics used by routing protocols are: Hop count - this is the number of routers a packet must travel through to get to its destination R1 --> R3 Bandwidth - this is the speed of a link also known as the data capacity of a link R1 --> R2 --> R3 15

16 16 Router Paths and Packet Switching Path determination is a process used by a router to pick the best path to a destination One of 3 path determinations results from searching for the best path Directly connected network Remote network No route determined

17 Using Static Routing 17

18 18 Dynamic Routing Protocols 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

19 19 The Role of Dynamic Routing Protocols Advantages of dynamic routing Automatically share information about remote networks Determine the best path to each network and add this information to their routing tables Compared to static routing, dynamic routing protocols require less administrative overhead Help the network administrator manage the time-consuming process of configuring and maintaining static routes Disadvantages of dynamic routing Dedicate part of a routers resources for protocol operation, including CPU time and network link bandwidth Times when static routing is more appropriate

20 20 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.

21 21 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

22 22 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

23 23 Classifying Routing Protocols Types of routing protocols: -Interior Gateway Protocols (IGP) -Exterior Gateway Protocols (EGP)

24 24 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

25 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. 25

26 Distance Vector or Link-State Routing Protocols Distance vector protocols use routers as sign posts along the path to the final destination. The only information a router knows about a remote network is the distance or metric to reach that network and which path or interface to use to get there. Distance vector routing protocols do not have an actual map of the network topology. Rumor based. A link-state routing protocol is like having a complete map of the network topology. The sign posts along the way from source to destination are not necessary, because all linkstate routers are using an identical map of the network. A link-state router uses the link-state information to create a topology map and to select the best path to all destination networks in the topology.

27 27 Routing protocol comparison Speed of Convergence - Speed of 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. Routing loops can occur when inconsistent routing tables are not updated due to slow convergence in a changing network. 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.

28 28 Routing protocol comparison Classful or Classless (Use of VLSM) - Classful routing protocols do not include the subnet mask and cannot support VLSM. Classless routing protocols include the subnet mask in the updates. Classless routing protocols support VLSM and better route summarization. Resource Usage - Resource usage includes the requirements of a routing protocol such as memory space (RAM), CPU utilization, and link bandwidth utilization. Higher resource requirements necessitate more powerful hardware to support the routing protocol operation, in addition to the packet forwarding processes.

29 29 Routing protocol comparison Implementation and 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.

30 30 Classifying Routing Protocols Convergence is defined as when all routers routing tables are at a state of consistency

31 31 Achieving Convergence Network converged when all routers have complete and accurate information about the entire network. Convergence time is the time it takes routers to share information, calculate best paths, and update their routing tables. A network is not completely operable until the network has converged. Convergence properties include the speed of propagation of routing information and the calculation of optimal paths. The speed of propagation refers to the amount of time it takes for routers within the network to forward routing information.

32 32 Routing Protocols Metrics Metric A value used by a routing protocol to determine which routes are better than others.

33 33 Routing Protocols Metrics Metrics used in IP routing protocols -Bandwidth -Cost -Delay -Hop count -Load -Reliability

34 34 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

35 35 Distance Vector Routing Protocols Distance Vector Technology The Meaning of Distance Vector: A router using distance vector routing protocols knows 2 things: Distance to final destination Vector, or direction, traffic should be directed

36 36 A router using a distance vector routing protocol does not have the knowledge of the entire path to a destination network. Instead the router knows only: The direction or interface in which packets should be forwarded The distance or how far it is to the destination network

37 Distance Vector Routing Protocols Characteristics of Distance Vector routing protocols: Periodic updates Neighbors Broadcast updates Entire routing table is included with routing update 37

38 Distance Vector Routing Protocols Routing Protocol Algorithm: -Defined as a procedure for accomplishing a certain task 38

39 Distance Vector Routing Protocols 39

40 40 Network Discovery Router initial start up (Cold Starts) -Initial network discovery Directly connected networks are initially placed in routing table

41 41 Network Discovery Initial Exchange of Routing Information If a routing protocol is configured then -Routers will exchange routing information Routing updates received from other routers -Router checks update for new information If there is new information: -Metric is updated -New information is stored in routing table

42 42 Network Discovery Exchange of Routing Information Router convergence is reached when -All routing tables in the network contain the same network information Routers continue to exchange routing information -If no new information is found then Convergence is reached

43 43 Network Discovery Convergence must be reached before a network is considered completely operable Speed of achieving convergence consists of 2 interdependent categories -Speed of broadcasting routing information -Speed of calculating routes

44 Network Discovery 44

45 45 Routing Table Maintenance Periodic Updates: RIPv1 & RIPv2 These are time intervals in which a router sends out its entire routing table.

46 46 Routing Table Maintenance Random Jitter Synchronized updates A condition where multiple routers on multi access LAN segments transmit routing updates at the same time. Problems with synchronized updates -Bandwidth consumption -Packet collisions Solution to problems with synchronized updates - Used of random variable called RIP_JITTER

47 47 Routing Table Maintenance RIP uses 4 timers -Update timer -Invalid timer -Holddown timer -Flush timer

48 48 Configuring Passive Interfaces Sending out unneeded updates on a LAN impacts the network in three ways: Wasted Bandwidth Wasted Resources Security Risk

49 49 Routing Table Maintenance Bounded Updates: EIGRP EIGRP routing updates are -Partial updates -Triggered by topology changes -Bounded -Non periodic

50 50 Routing Table Maintenance Triggered Updates Conditions in which triggered updates are sent -Interface changes state -Route becomes unreachable -Route is placed in routing table

51 51 Routing Loops Routing loops are A condition in which a packet is continuously transmitted within a series of routers without ever reaching its destination.

52 52 Routing Loops Routing loops may be caused by: -Incorrectly configured static routes -Incorrectly configured route redistribution -Slow convergence -Incorrectly configured discard routes Routing loops can create the following issues -Excess use of bandwidth -CPU resources may be strained -Network convergence is degraded -Routing updates may be lost or not processed in a timely manner

53 53 Routing Loops Count to Infinity This is a routing loop whereby packets bounce infinitely around a network.

54 54 Routing Loops Setting a maximum Distance Vector routing protocols set a specified metric value to indicate infinity Once a router counts to infinity it marks the route as unreachable

55 55 Routing Loops Preventing loops with holddown timers -Holddown timers allow a router to not accept any changes to a route for a specified period of time. -Point of using holddown timers Allows routing updates to propagate through network with the most current information.

56 56 Routing Loops The Split Horizon Rule is used to prevent routing loops Split Horizon rule: A router should not advertise a network through the interface from which the update came.

57 57 Routing Loops Split horizon with poison reverse The rule states that once a router learns of an unreachable route through an interface, advertise it as unreachable back through the same interface

58 58 Routing Loops IP & TTL Purpose of the TTL field The TTL field is found in an IP header and is used to prevent packets from endlessly traveling on a network How the TTL field works -TTL field contains a numeric value The numeric value is decreased by one by every router on the route to the destination. If numeric value reaches 0 then Packet is discarded.

59 59 Routing Protocols Today Factors used to determine whether to use RIP or EIGRP include -Network size -Compatibility between models of routers -Administrative knowledge

60 60 Routing Protocols Today RIP Features of RIP: -Supports split horizon & split horizon with poison reverse -Capable of load balancing -Easy to configure -Works in a multi vendor router environment

61 61 Routing Protocols Today EIGRP Features of EIGRP: Triggered updates EIGRP hello protocol used to establish neighbor adjacencies Supports VLSM & route summarization Use of topology table to maintain all routes Classless distance vector routing protocol Cisco proprietary protocol basic functionality of EIGRP released as an open standard

62 62 Marsruutimisprotokollid Distance vector Marsruudid sisaldavad kaugust ja suunda Kaugusel mingi mõõt (hüpete arv) Suund on järgmine marsruuter või väljumis võrguliides Parim tee naabritelt info Naaber X võrku Z on 4 hüpet Naaber Y võrku Z on 8 hüpet Valib tee läbi naabri X Ei tea kogu teed lõpp punkti Teab, et kas läbi X või Y, kuidas võrk sealt edasi välja näeb ei tea RIP, EIGRP

63 63 Marsruutimisprotokollid Link state The basic concept of link-state routing is that every node constructs a map of the connectivity to the network, in the form of a graph, showing which nodes are connected to which other nodes. Saadetakse infot ühendatud linkide oleku kohta ja info teiste marsruuterite kohta Protokollid Open Shortest Path First (OSPF) Intermediate System-to-Intermediate System (IS-IS)

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65 65 Link-State Routing Steps Each routers learns about its own directly connected networks Link state routers exchange hello packet to meet other directly connected link state routers. Each router builds its own Link State Packet (LSP) which includes information about neighbors such as neighbor ID, link type, & bandwidth. After the LSP is created the router floods it to all neighbors who then store the information and then forward it until all routers have the same information. Once all the routers have received all the LSPs, the routers then construct a topological map of the network which is used to determine the best routes to a destination

66 66 Directly Connected Networks Link - This is an interface on a router Link state - This is the information about the state of the links

67 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 67

68 Establish Neighbor Adjacencies 68

69 69 Establish Neighbor Adjacencies DR and BDR election only occurs on multi-access networks such as Ethernet LANs.

70 OSPF DR and BDR 70

71 71 OSPF Designated Router Designated Router (DR) is the solution to managing adjacencies and flooding of LSAs on a multiaccess network. Backup Designated Router (BDR) also elected in case DR fails. All other Routers DROTHER only form adjacencies with the DR and BDR. DROTHERs only send their LSAs to the DR and BDR using the multicast address DR uses the multicast address to send LSAs to all other routers. DR only router flooding LSAs. DR/BDR Elections only necessary on multiaccess networks.

72 Default DR/BDR Election Process The router with the highest interface priority is elected as the DR. The router with the second highest interface priority is elected as the BDR. Priority can be configured between Priority of 0 - router cannot become the DR. If interface priorities are equal then the router with highest router ID is elected DR and second highest the BDR 3 ways to determine router ID: Router ID can be manually configured. If not configured, ID determined by highest loopback IP address. If no loopbacks, ID is determined by the highest active IPv4 address. In an IPv6 network, Router ID must be configured manually.

73 73 Building the Link State Packet Each router builds its own Link State Packet (LSP) Contents of LSP: -State of each directly connected link -Includes information about neighbors such as neighbor ID, link type & bandwidth.

74 Building the Link State Packet 74

75 75 Flooding LSPs to Neighbors Once LSP are created they are forwarded out to neighbors. -After receiving the LSP the neighbor continues to forward it throughout routing area.

76 Link-State Routing 76

77 Shortest Path First (SPF) Tree Building a portion of the SPF tree Process begins by examining R2 s LSP information -R1 ignores 1st LSP Reason: R1 already knows it s connected to R2 77

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83 Building a portion of the SPF tree R1 uses LSP from R2 Reason: R1 learns that R2 is connected to /16. This link is added to R1 s SPF tree. R2 has a network /16 with a cost of 2 and no neighbors This link is added to R1's SPF tree. 83

84 Building a portion of the SPF tree R1 uses 3rd LSP Reason: R1 learns that R3 is connected to /16. This link is added to R1 s SPF tree. R3 has a network /16 with a cost of 2 and no neighbors This link is added to R1's SPF tree. 84

85 85 Determining the shortest path The shortest path to a destination determined by adding the costs & finding the lowest cost

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87 87 Determining the shortest path Once the SPF algorithm has determined the shortest path routes, these routes are placed in the routing table.

88 Determining the shortest path 88

89 89 OSPF OSPF does not use a Transport layer protocol, as OSPF packets are sent directly over IP. Protocol Number 89

90 90 OSPF packet types Hello - Hello packets are used to establish and maintain adjacency with other OSPF routers. DBD - The Database Description (DBD) packet contains an abbreviated list of the sending router's link-state database and is used by receiving routers to check against the local link-state database. LSR - Receiving routers can then request more information about any entry in the DBD by sending a Link- State Request (LSR).

91 91 OSPF packet types LSU - Link-State Update (LSU) packets are used to reply to LSRs as well as to announce new information. LSUs contain seven different types of Link-State Advertisements (LSAs). LSUs and LSAs are briefly discussed in a later topic. LSAck - When an LSU is received, the router sends a Link-State Acknowledgement (LSAck) to confirm receipt of the LSU.

92 92 Hello packets Discover OSPF neighbors and establish neighbor adjacencies. Advertise parameters on which two routers must agree to become neighbors. Elect the Designated Router (DR) and Backup Designated Router (BDR) on multiaccess networks like Ethernet and Frame Relay. Multicast address

93 93 OSPF routers are sending Hello packets on all OSPFenabled interfaces to determine if there are any neighbors on those links. Receiving an OSPF Hello packet on an interface confirms for a router that there is another OSPF router on this link.

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95 OSPF Authentication Purpose is to encrypt & authenticate routing information This is an interface specific configuration Routers will only accept routing information from other routers that have been configured with the same password or authentication information 95

96 96 OSPF Metric OSPF uses cost as the metric for determining the best route The best route will have the lowest cost Cost is based on bandwidth of an interface Cost is calculated using the formula 10 8 / bandwidth Reference bandwidth defaults to 100Mbps

97 97 Cost: Example Strategy 100GE 100Gbps cost = 1 40GE/OC768 40Gbps cost = 2 10GE/OC192 10Gbps cost = 5 OC48 2.5Gbps cost = 10 GigEthernet 1Gbps cost = 20 OC12 622Mbps cost = 50 OC3 155Mbps cost = 100 FastEthernet 100Mbps cost = 200 Ethernet 10Mbps cost = 500 E1 2Mbps cost = 1000

98 98 Advantages of Link State Builds a Topological Map - Link-state routing protocols create a topological map, or SPF tree of the network topology. Because link-state routing protocols exchange link-states, the SPF algorithm can build an SPF tree of the network. Using the SPF tree, each router can independently determine the shortest path to every network. Fast Convergence - When receiving an LSP, link-state routing protocols immediately flood the LSP out all interfaces except for the interface from which the LSP was received. In contrast, RIP needs to process each routing update and update its routing table before flooding them out other interfaces.

99 99 Advantages of Link State Event-driven Updates - 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 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.

100 100 OSPF head omadused Low Bandwidth Utilisation Only changes propagated Uses multicast on multi-access broadcast networks

101 101 OSPF head omadused Fast Convergence Detection Plus LSA/SPF LSA flooded throughout area Acknowledgement based Topology database synchronised Each router derives routing table to destination network

102 102 Disadvantages of Link State Memory Requirements - Link-state protocols require additional memory to create and maintain the link-state database and SPF tree. Processing Requirements - Link-state protocols can also require more CPU processing than distance vector routing protocols. The SPF algorithm requires more CPU time than distance vector algorithms such as Bellman-Ford, because link-state protocols build a complete map of the topology. Bandwidth Requirements - The flooding of link-state packets can adversely affect the available bandwidth on a network. This should only occur during initial startup of routers, but can also be an issue on unstable networks.

103 Single-Area OSPF Single-area OSPF is useful in smaller networks. If an area becomes too big, the following issues must be addressed: Large routing table (no summarization by default) Large link-state database (LSDB) Frequent SPF algorithm calculations

104 Single-Area OSPF

105 105 OSPF and Multiaccess Networks Challenges in Multiaccess Networks OSPF defines five network types: Point-to-point Broadcast Multiaccess Nonbroadcast Multiaccess (NBMA) Point-to-multipoint Virtual links

106 106 OSPF in Multiaccess Networks 2 challenges presented by multiaccess networks Multiple adjacencies Extensive LSA flooding

107 107 Extensive flooding of LSAs For every LSA sent out there must be an acknowledgement of receipt sent back to transmitting router. consequence: lots of bandwidth consumed and chaotic traffic

108 108 Solution to LSA flooding issue Designated router (DR) Backup designated router (BDR) DR & BDR selection Routers are elected to send & receive LSA Sending & Receiving LSA DRothers send LSAs via multicast to DR & BDR DR forward LSA via multicast address to all other routers

109 109 Criteria for getting elected DR/BDR 1. DR: Router with the highest OSPF interface priority. 2. BDR: Router with the second highest OSPF interface priority. 3. If OSPF interface priorities are equal, the highest router ID is used to break the tie.

110 110 Tuning OSPF Forcibly set your DR and BDR per segment so that they are known Choose your most powerful, or most idle routers, so that OSPF converges as fast as possible under maximum network load conditions Try to keep the DR/BDR limited to one segment each

111 Multiarea OSPF Multiarea OSPF requires a hierarchical network design and the main area is called the backbone area (area 0) and all other areas must connect to the backbone area.

112 Disadvantages of Link-State Protocols 112

113 113 OSPF Areas Area is a group of contiguous hosts and networks Reduces routing traffic Per area topology database Invisible outside the area Backbone area MUST be contiguous All other areas must be connected to the backbone

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115 115 OSPF Two-Layer Area Hierarchy Multiarea OSPF is implemented in a two-layer area hierarchy: Backbone (Transit) area - Area whose primary function is the fast and efficient movement of IP packets. Interconnect with other OSPF area types Called OSPF area 0 which all other areas directly connect Regular (Non-backbone) area - Connects users and resources A regular area does not allow traffic from another area to use its links to reach other areas

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117 Types of OSPF Routers

118 Types of OSPF Routers

119 OSPF Route Types 119

120 120 Addressing for Areas Assign contiguous ranges of subnets per area to facilitate summarisation