Routing Protocols and Concepts – Chapter 11 potx

OSPF (Single Area OSPF) Routing Protocols and Concepts – Chapter 11 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 1 Introduction •In this chapter, you will learn basic, single-area OSPF implementations and configurations ITE PC v4.0 Chapter 1 2 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public and configurations . •More complex OSPF configurations and concepts (multi-areas OSPF) are reserved for CCNP-level courses. Introduction to OSPF 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 p ublished in RFC 2740 p ITE PC v4.0 Chapter 1 3 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Introduction to OSPF Introduction to OSPF OSPF Message Encapsulation  OSPF packet type OSPF packet type – There exist 5 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, D es tin a ti o n IP add r ess, & Pr o t oco l es a o add ess, & o oco field set to 89. the destination address is set to one of two multicast addresses: 224.0.0.5 or 224006 224 . 0 . 0 . 6 .  Data Link Frame Header – Contains - destination MAC address is ITE PC v4.0 Chapter 1 4 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public also a multicast address: 01-00-5E-00- 00-05 or 01-00-5E-00-00-06. I t d ti t OSPF I n t ro d uc ti on t o OSPF 5 OSPF Packet Types:  1. Hello - Hello packets are used to establish and maintain adjacency with other OSPF routers.  2. DBD - The Database Description (DBD) packet contains an abbre iated list of the sending ro ter's contains an abbre v iated list of the sending ro u ter's link-state database and is used by receiving routers to check against the local link-state database.  3. LSR - Receiving routers can then request more information about any entry in the DBD by sending a Link-State Request (LSR).  4. LSU - Link-State Update (LSU) packets are used to reply to LSRs as well as to announce new information. – LSUs contain 7 different types of Link-State Advertisements (LSAs). –LSUs and LSAs are discussed in a later topic. 5LSAk Wh LSU i i d th t ITE PC v4.0 Chapter 1 5 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public  5 . LSA c k - Wh en an LSU i s rece i ve d , th e rou t er sends a Link-State Acknowledgement (LSAck) to confirm receipt of the LSU. OSPF: Hello Protocol OSPF: Hello Protocol  Purpose of Hello Packet  Discover OSPF neighbors & establish adjacencies  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 sending interface  Hello Interval: number of seconds between the sending router's hellos  Router Priority: Used in DR/BDR election (discussed lt ) l a t er )  Designated Router (DR): Router ID of the DR, if any  Backup Designated Router (BDR): Router ID of the BDR, if any ITE PC v4.0 Chapter 1 6 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public  List of Neighbors: lists the OSPF Router ID of the neighboring router(s) OSPF: Hello Protocol OSPF: Hello Protocol  Establish adjacencies: – The y must a g ree on three values: Hello Why 10 second hello interval Also need to have the same Area ID. yg interval, Dead interval, and network type.  OSPF Hello Intervals –Hello interval indicates how often an OSPF router transmits its Hello packets Why 10 second hello interval communications consider better than the 30 second routing update for RIP? router transmits its Hello packets –Usually multicast (224.0.0.5) for ALLSPFRouters – sent ever y 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 4 times the hello interval – For multiaccess and point - to - point segments For multiaccess and 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 ITE PC v4.0 Chapter 1 7 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public – If the Dead interval expires before the routers receive a Hello packet, OSPF will remove that neighbor from its link-state database. OSPF: Hello Protocol  To reduce the amount of OSPF traffic on To reduce the amount of OSPF traffic on multiaccess networks, OSPF elects a Designated Router (DR) and Backup Desi g nated Router ( BDR ) . g()  Hello protocol packets contain information that is used in electing DR and BDR The DR is responsible for updating all other – The DR is responsible for updating all other OSPF routers (called DROthers) when a change occurs in the multiaccess network. – The BDR monitors the DR and takes over as The BDR monitors the DR and takes over as DR if the current DR fails.  In the figure, R1, R2, and R3 are connected through point to point links Therefore no More detail discussion through point - to - point links . Therefore , no DR/BDR election occurs. –The DR/BDR election and processes will be discussed in a later topic and the topology will More detail discussion on the DR, BDR, DROther later. You need to know this for ITE PC v4.0 Chapter 1 8 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public discussed in a later topic and the topology will be changed to a multiaccess network. need to know this for CCNA exam. Introduction to OSPF Introduction to OSPF OSPF Link-state Updates  Purpose of a Link State Update (LSU) 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 1 9 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public Introduction to OSPF Introduction to OSPF OSPF Algorithm  OSPF routers build & maintain link-state dtb tii LSA d a t a b ase con t a i n i ng LSA received from other routers routers 1. Information found in database is utilized upon e ec tion of Dijkstra SPF e x ec u tion of Dijkstra SPF algorithm 2. SPF al g orithm used to g create SPF tree 3. SPF tree used to populate routing table ITE PC v4.0 Chapter 1 10 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public routing table [...]... Verifying OSPF Show ip protocols –OSPF process ID, p , –the router ID, –networks the router is advertising, –the default administrative distance, 110 for OSPF Show ip ospf –OSPF process ID –router ID router ID –OSPF area information –the last time the SPF algorithm was calculated •R1 has participated in during the past 11 and a half hours is to send small Hello packets to its neighbors –SPF schedule delay... links? ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 35 Basic OSPF Configuration Modifying the Cost of a link Both id B th sides of a serial li k should b f i l link h ld be configured with the same bandwidth –Commands used to modify bandwidth value Commands Bandwidth command –Example: Router(config-if)#bandwidthbandwidth-kbps ip ospf cost command – allows you to directly... than the default bandwidth –This makes it imperative that the b d idth value reflects Thi k i ti th t th bandwidth l fl t link’s actual speed Reason: so routing table has best path information The show interface command will display interface’s interface s bandwidth –Most serial link default to 1.544Mbps –However, some serial interfaces may default to 128 kbps However, ITE PC v4.0 Chapter 1 © 2007 Cisco... the router-id command, we will use the loopback address method for assigning router IDs IDs ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 24 Quick Review We just went over 3 different types of ID ospf process-id – OSPF process process – Cannot be 0 Area ID: – OFPS area – If it is the first, and the backbone area, it is 0 , , Router ID – Router ID – 1 IP address is... v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 20 Basic OSPF Configuration OSPF Router ID Commands used to verify current router ID –Show ip protocols –Show ip ospf –Show ip ospf interface ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 21 Basic OSPF Configuration OSPF Router ID Router ID (not configured) & Loopback addresses (configured) –Highest... network as the cost value -Cost i b C is based on b d id h of an i d bandwidth f interface f Cost is calculated using the formula 108 / bandwidth -Reference bandwidth The 100Mbps (FastEthernet) and higher will have the same OSPF cost of 1 This reference bandwidth can be modified using auto-cost reference-bandwidth command ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public... Distance Default Administrative Distance for OSPF is 110 ITE PC v4.0 Chapter 1 © 2007 Cisco Systems, Inc All rights reserved Cisco Public 11 Introduction to OSPF OSPF Authentication –It is good practice to authenticate transmitted It routing information –This is an interface specific configuration p g –This practice ensures that routers will only accept routing information from other routers that have... Mbps or 1544 kbps kbps 2A/S ITE PC v4.0 Chapter 1 2T © 2007 Cisco Systems, Inc All rights reserved COD has these 2 types of serial cards in the lab Cisco Public 34 OSPF Metric: Bandwidth Remember, this bandwidth value does not actually affect the speed of the link; it is used by some routing protocols to compute the routing metric –It is important that the bandwidth value reflect th actual speed of... their states displayed as 2WAY 2WAY –This will be discussed in a DR and BDR section Two routers may not form an OSPF adjacency if dj if: –The subnet masks do not match, causing the routers to be on separate networks –OSPF Hello or Dead Timers do not match –OSPF Network Types do not match –There is a missing or i Th i i i incorrect OSPF t network command ITE PC v4.0 Chapter 1 •Neighbor ID - The router... loopback address will be used as router ID Highest –Advantage of using loopback address the loopback interface cannot fail OSPF stability The OSPF router id command router-id –Introduced in IOS 12.0 –OSPF router-id command, which is a fairly recent addition to IOS, it is more common to find loopback , p addresses used for configuring OSPF router IDs –Command syntax Router(config)#router ospf process-id . OSPF (Single Area OSPF) Routing Protocols and Concepts – Chapter 11 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public ITE PC v4.0 Chapter 1 1 Introduction •In this chapter, you will learn. implementations and configurations ITE PC v4.0 Chapter 1 2 © 2007 Cisco Systems, Inc. All rights reserved. Cisco Public and configurations . •More complex OSPF configurations and concepts (multi-areas. second routing update for RIP? router transmits its Hello packets –Usually multicast (224.0.0.5) for ALLSPFRouters – sent ever y 10 seconds on multiaccess and y point-to-point segments –Sent