Giao thức định tuyến - Chapter 11 potx

OSPF (Single Area OSPF) Routing Protocols and Concepts – Chapter 11 ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public Introduction •In this chapter, you will learn basic, single-area OSPF implementations and configurations configurations •More complex OSPF configurations and concepts (multi-areas OSPF) are reserved for CCNP-level courses ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public Introduction to OSPF Background of OSPF Began in 1987 1989 OSPFv1 released in RFC 1131 This version was experimental & never deployed 1991 OSPFv2 released in RFC 1247 1998 OSPFv2 updated in RFC 2328 1999 OSPFv3 published in RFC 2740 p ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public Introduction to OSPF OSPF Message Encapsulation OSPF packet type – There exist types (next slide) OSPF packet header –Contains - Router ID an area ID and Type code for OSPF packet type IP packet header – Contains - Source IP address, Destination IP add ess, & Protocol es a o address, o oco field set to 89 the destination address is set to one of two multicast addresses: 224.0.0.5 or 224.0.0.6 224 0 Data Link Frame Header –Contains - destination MAC address is also a multicast address: 01-00-5E-0000-05 or 01-00-5E-00-00-06 ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public Introduction t I t d ti to OSPF 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 abbre iated list of the sending ro ter's abbreviated 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) LSU - Link-State Update (LSU) packets are used to reply to LSRs as well as to announce new information –LSUs contain different types of Link-State Advertisements (LSAs) –LSUs and LSAs are discussed in a later topic LSAck When LSA k - Wh an LSU is received, th router i i d the t sends a Link-State Acknowledgement (LSAck) to confirm receipt of the LSU ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public OSPF: Hello Protocol Purpose of Hello Packet Discover OSPF neighbors & establish adjacencies Advertise parameters on which routers must agree to become neighbors Used by multi-access networks to elect a Designated Router and a Backup Designated Router Type: OSPF Packet Type: Hello (1), DD (2), LS Request (3), LS Update (4), LS ACK (5) Router ID: ID of the originating router Area ID: area from which the packet originated Network Mask: Subnet mask associated with the sending interface Hello Interval: number of seconds between the sending router's hellos Router Priority: Used in DR/BDR election (discussed later) l t ) Designated Router (DR): Router ID of the DR, if any Backup Designated Router (BDR): Router ID of the BDR, if any List of Neighbors: lists the OSPF Router ID of the neighboring router(s) ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public OSPF: Hello Protocol Also need to have the same Area ID Establish adjacencies: – They must agree on three values: Hello y g interval, Dead interval, and network type OSPF Hello Intervals Why 10 second hello interval communications consider better than the 30 second routing update for RIP? –Hello interval indicates how often an OSPF router transmits its Hello packets –Usually multicast (224.0.0.5) for ALLSPFRouters –sent every 10 seconds on multiaccess and y point-to-point segments –Sent every 30 seconds for NBMA segments OSPF Dead Intervals –This is the time that must transpire before the neighbor is considered down –Default time is times the hello interval –For multiaccess and point-to-point segments, For point to point segments this period is 40 seconds –For NBMA networks, the Dead interval is 120 seconds –If the Dead interval expires before the routers If receive a Hello packet, OSPF will remove that neighbor from its link-state database ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public OSPF: Hello Protocol To reduce the amount of OSPF traffic on multiaccess networks, OSPF elects a Designated Router (DR) and Backup Designated Router ( g (BDR) ) Hello protocol packets contain information that is used in electing DR and BDR –The DR is responsible for updating all other The OSPF routers (called DROthers) when a change occurs in the multiaccess network –The BDR monitors the DR and takes over as The DR if the current DR fails In the figure, R1, R2, and R3 are connected through point to point links Therefore no point-to-point links Therefore, DR/BDR election occurs –The DR/BDR election and processes will be discussed in a later topic and the topology will be changed to a multiaccess network ITE PC v4.0 Chapter More detail discussion on the DR, BDR, DROther later You need to know this for CCNA exam © 2007 Cisco Systems, Inc All rights reserved Cisco Public Introduction to OSPF OSPF Link-state Updates Purpose of a Link State Update (LSU) –Used to deliver link state advertisements Purpose of a Link State Advertisement (LSA) –Contains information about neighbors & path costs –An LSU packet can contain 11 different types of LSAs, ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public Introduction to OSPF OSPF Algorithm OSPF routers build & maintain link-state database containing LSA d t b t i i received from other routers Information found in database is utilized upon execution e ec tion of Dijkstra SPF algorithm SPF algorithm used to g create SPF tree SPF tree used to populate routing table ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 10 OSPF in Multiaccess Networks OSPF Interface Priority Modify Priority –Router(config-if)#ip ospf priority {0 - 255} Force Election –After d i a shutdown and a no shutdown Aft doing h td d h td on the FastEthernet 0/0 interfaces of all three routers, we see the result of the change of OSPF interface priorities –The show ip ospf neighbor command on RouterC now shows that RouterA (Router ID 192.168.31.11) is the DR with the highest OSPF interface priority of 200 p y –RouterB (Router ID 192.168.31.22) is still the BDR with the next highest OSPF interface priority of 100 –Notice f N ti from R t A' output of show ip RouterA's t t f h i ospf neighbor that it does not show a DR, because RouterA is the actual DR on this network ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved DR BDR Cisco Public 57 More OSPF Configuration Redistributing Redistrib ting an OSPF Defa lt Ro te Default Route Topology includes a link to ISP –Router connected to ISP R t t dt In this topology, the Called an autonomous system border router Loopback1 (Lo1) simulate the connection to another Used to propagate a default route router –Example of static default route R1(config)#ip route 0.0.0.0 0.0.0.0 loopback –Requires the use of the default-information originate command –Example of default-information originate command R1(config-router)#default-information originate ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 58 Redistributing an OSPF Default Route The default route in R2 and R3 with the routing source OSPF, but with the additional code, E2 For R2, the route is: O*E2 0.0.0.0/0 [110/1] via 192.168.10.10, 00:05:34, Serial0/0/1 E2 denotes that this route is an OSPF External Type route the cost of an E2 route is always the external cost, irrespective of the interior cost to reach that route (CCNP) ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 59 More OSPF Configuration Fine-Tuning OSPF Since link speeds are getting faster it may be necessary to change reference bandwidth f values –Do this using the auto cost Do auto-cost reference-bandwidth command –Example: R1(config-router)#auto-cost reference-bandwidth 10000 •the default value is equivalent to 100 To increase it to 10GigE speeds, y would need g p , you to change the reference bandwidth to 10000 •Again, make sure you configure this command on all routers in the OSPF routing domain ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 60 More OSPF Configuration Fine-Tuning OSPF R1(config-router)#autocost reference-bandwidth 10000 •the default value is equivalent to 100 To increase it to 10GigE speeds you would need speeds, to change the reference bandwidth to 10000 R1 Before, the cost to 10.10.10.0/24 is 1172 After Aft configuring a new reference b d idth fi i f bandwidth, the cost for the same route is now 117287 ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 61 More OSPF Configuration Fine-Tuning OSPF Modifying OSPF timers –Reason to modify timers Faster detection of network failures –Manually modifying Hello & Dead intervals Router(config-if)#ip ospf hello-interval seconds Router(config-if)#ip ospf dead-interval seconds R t ( fi if)#i fd di t l d –Point to be made Hello & Dead intervals must be the same between neighbors ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 62 The End Questions? What will be the result of the DR and BDR elections for this single area OSPF network? (Choose three.) * Decision process: HQ will be DR for 10.4.0.0/16 ill b f 10 0/16 Router A will be DR for 10.4.0.0/16 HQ will be BDR for 10.4.0.0/16 10 0/16 Router A will be DR for 10.5.0.0/16 Remote will be DR for 10.5.0.0/16 10 0/16 Remote will be BDR for 10.5.0.0/16 ITE PC v4.0 Chapter Which segment will have election? Priority? Router ID (each router will only has ID)? Set using “router-ID” command Highest Loopback IP address? Highest physical IP address (include serial interface)? © 2007 Cisco Systems, Inc All rights reserved Cisco Public 63 The End Questions? The routers in the diagram are configured as shown The loopback interface on shown router R1 is labeled as lo0 All OSPF priorities are set to the default except for Ethernet0 of router R2, which has an OSPF priority of What will be the result of the OSPF DR/BDR elections on the 192.1.1.0 network? (Choose two.) R1 will be the DR R1 will be the BDR R2 will be the DR * Decision process: 1 Which segment will have election? Priority? Router ID (each router will only has ID)? R2 will be the BDR Set using “router-ID” command R3 will be the DR Highest Loopback IP address? R3 will be the BDR ITE PC v4.0 Chapter 1 Highest physical IP address (include serial interface)? © 2007 Cisco Systems, Inc All rights reserved Cisco Public 64 Questions? * Decision process: 1 Which segment will have election? Priority? Router ID (each router will only has ID)? Highest Loopback IP address? ITE PC v4.0 Chapter Set using “router-ID” command Highest physical IP address (include serial interface)? © 2007 Cisco Systems, Inc All rights reserved Cisco Public 65 Questions? Answer????? * Decision process: Which segment will have election? 2 Priority? i i ? Router ID (each router will only has ID)? Highest Loopback IP address? ITE PC v4.0 Chapter Set using “router-ID” command router ID Highest physical IP address (include serial interface)? i li f )? © 2007 Cisco Systems, Inc All rights reserved Cisco Public 66 Questions? Answer????? HQ will be DR for 10.4.0.0/16 Router A will be DR for 10.4.0.0/16 HQ will b BDR f ill be for 10.4.0.0/16 * Decision process: Router A will be DR for 10.5.0.0/16 1 Which segment will have election? Priority? Remote will be DR for 10.5.0.0/16 Router ID (each router will only has ID)? Remote will be BDR for 10.5.0.0/16 10 0/16 ITE PC v4.0 Chapter 1 Set using “router-ID” command Highest Loopback IP address? Highest physical IP address (include serial interface)? © 2007 Cisco Systems, Inc All rights reserved Cisco Public 67 Summary RFC 2328 describes OSPF link state concepts and operations OSPF Characteristics –A commonly deployed link state routing protocol –Employs DRs & BDRs on multi-access networks DRs & BDRs are elected DR & BDRs are used to transmit and receive LSAs –Uses packet types: Uses 1: HELLO 2: DATABASE DESCRIPTION 3: LINK STATE REQUEST 4: LINK STATE UPDATE 5: LINK STATE ACKNOWLEDGEMENT ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 68 Summary OSPF Characteristics –Metric = cost Lowest cost = best path Configuration –Enable OSPF on a router using the following command E bl t i th f ll i d R1(config)#router ospf process-id –use the network command to define which interfaces will use participate in a given OSPF process R1(config-router)#network network-address wildcard-mask area area-id ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 69 Summary Verifying OSPF configuration –Use the following commands show ip protocol show ip route show i ospf i t f h ip f interface show ip ospf neighbor ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 70 ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights reserved Cisco Public 71 ... 224.0.0.6 224 0 Data Link Frame Header –Contains - destination MAC address is also a multicast address: 0 1-0 0-5 E-000 0-0 5 or 0 1-0 0-5 E-0 0-0 0-0 6 ITE PC v4.0 Chapter © 2007 Cisco Systems, Inc All rights... wildcard-ask Router(config-router)#network network-address wildcard ask area area-id area id 255.255.255.255 - 255.255.255.240 -0 0 15 0 255.255.255.255 - 255.255.255.252 -0 0... ospf process-id Router(config-router)#router-id ip-address Modifying the Router ID –Use the command Router#clear ip ospf process Use This command does not work in PT ITE PC v4.0 Chapter © 2007