Junos Intermediate Routing

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Junos Intermediate Routing Chapter 4: Open Shortest Path First 2012 Juniper

2 Chapter Objectives After successfully completing this chapter, you will be able to: Explain the operations of OSPF Describe the role of the designated router List and describe OSPF area types Configure, monitor, and troubleshoot OSPF 4-2

3 Agenda: Open Shortest Path First Overview of OSPF Adjacency Formation and the DR Election OSPF Scalability Configuring and Monitoring OSPF Basic OSPF Troubleshooting 4-3

4 An Overview of OSPF OSPF is a link-state IGP used within an AS OSPF floods link-state advertisements OSPF routers use the received LSAs to create a complete database of the network OSPF uses the shortest-path-first algorithm to calculate the best path to each destination network OSPF ISP X AS AS

The Link-State Database All OSPF routers maintain a copy of the database Database contents consist of information learned through LSAs and must match on all

5 The Link-State Database All OSPF routers maintain a copy of the database Database contents consist of information learned through LSAs and must match on all routers within an area SPF algorithm uses the contents of the link-state database as input data to calculate network paths R2 R1 R3 OSPF Area 0 R

6 OSPF Packet Types The five OSPF packet types include: Type 1 Type 2 Type 3 Type 4 Type 5 Hello Database Description Link-State Request Link-State Update Link-State Acknowledgment Link-state advertisements are flooded reliably using link-state requests, link-state updates, and link-state acknowledgments. R1 Link-State Request Link-State Update Link-State Acknowledgment R

7 Hello Packet Type 1 Type 2 Type 3 Type 4 Type 5 Hello Database Description Link-State Request Link-State Update Link-State Acknowledgment Multicast hello packets are used to establish and maintain OSPF neighbor relationships Sent to all OSPF routers address Consist of the OSPF header plus the following fields: Network mask* Hello interval* Dead interval* Options* Router priority Designated router Backup designated router Neighbor * Fields that must match to form an adjacency over a broadcast medium; a matching network mask is not required for point-to-point links 4-7

8 Database Description Packet Type 1 Type 2 Type 3 Type 4 Type 5 Hello Database Description Link-State Request Link-State Update Link-State Acknowledgment Database description packets are exchanged during adjacency formation to determine which router is in charge of the database exchange Describe the contents of the link-state database and consist of the OSPF header, a sequence number, and LSA headers 4-8

9 Link-State Request Packet Type 1 Type 2 Type 3 Type 4 Type 5 Hello Database Description Link-State Request Link-State Update Link-State Acknowledgment Link-state request packets are sent by an OSPF router when that router detects its database is stale Used to request precise version of database and consist of the OSPF header, link-state type, link-state ID, and advertising router R1 Link-State Request Link-State Update Link-State Acknowledgment R

10 Link-State Update Packet Type 1 Type 2 Type 3 Type 4 Type 5 Hello Database Description Link-State Request Link-State Update Link-State Acknowledgment Link-state update packets are the basic information block in OSPF and can carry multiple LSAs Transmitted using multicast to either the all OSPF routers address ( ) or the all DRs address ( ), and consist of the OSPF header, number of advertisements, and LSAs R1 R2 Link-State Request Link-State Update Link-State Acknowledgment

11 Link-State Acknowledgment Packet Type 1 Type 2 Type 3 Type 4 Type 5 Hello Database Description Link-State Request Link-State Update Link-State Acknowledgment Link-state acknowledgment packets are received in response to link-state update packets A single acknowledgment packet can include responses to multiple update packets and consist of the OSPF header and the LSA header R1 Link-State Request Link-State Update Link-State Acknowledgment R

12 Agenda: Open Shortest Path First Overview of OSPF Adjacency Formation and the DR Election OSPF Scalability Configuring and Monitoring OSPF Basic OSPF Troubleshooting

13 Adjacency Formation R1 R2 Down 2Way ExStart Exchange Hello (DR=0, Seen = 0) Hello (DR=RT2, Seen = RT1) Hello (DR=RT2, Seen = RT2) DD (Seq=x, Master) DD (Seq=y, Master) DD (Seq=y, Slave) DD (Seq=y+1, Master) DD (Seq=y+1, Slave) Down Init 2Way ExStart Exchange Loading Full DD (Seq=y+n, Master) DD (Seq=y+n, Slave) LS Request LS Update LS Request LS Update Full

14 Adjacency Optimization (1 of 3) By default, OSPF attempts to form adjacencies with all neighbors discovered on all interfaces On a broadcast media like Ethernet, this approach is suboptimal because it would require a full mesh of adjacencies Adjacencies

15 Adjacency Optimization (2 of 3) OSPF elects a DR to represent the segment Minimizes OSPF processes and reduces traffic on segment A BDR is also elected to recover if the DR fails DR BDR OSPF adjacencies are only formed with the DR and BDR. DR DR DROther DROther DROther

16 Adjacency Optimization (3 of 3) OSPF interface type point-to-point Used between adjacencies involving exactly two neighbors No DR/BDR election occurs Saves time getting the adjacency to a Full state Useful on back-to-back Ethernet links [edit protocols ospf] user@r1# show area { interface ge-1/0/0.0 { interface-type p2p; user@r1> show ospf interface Interface State Area DR ID BDR ID Nbrs ge-1/0/0.0 PtToPt

17 Electing the Designated Router Every OSPF router has a DR election priority Priority range is (default is 128) If two routers share the highest priority, the router with the highest RID is elected The election of a DR is a nondeterministic event An existing DR will not be replaced The first router on the segment within 40 seconds wins DR BDR Priority: 255 RID: DR DR Priority: 128 RID:

18 OSPF Neighbors Versus Adjacencies R1 (RID: ) R2 (RID: ) Adjacencies DR BDR DROther 2-way DROther R3 (RID: ) R4 (RID: ) show ospf neighbor Address Interface State ID Pri Dead ge-0/0/1.0 Full ge-0/0/1.0 Full ge-0/0/1.0 Full show ospf neighbor Address Interface State ID Pri Dead ge-0/0/1.0 Full ge-0/0/1.0 Full ge-0/0/1.0 2Way

19 Agenda: Open Shortest Path First Overview of OSPF Adjacency Formation and the DR Election OSPF Scalability Configuring and Monitoring OSPF Basic OSPF Troubleshooting

20 Scaling an OSPF Network Problem: As OSPF networks grow, so does the size of the link-state database, which can overload resources Area 0 Area 0 Solution: Implement OSPF areas to shrink the size of the link-state database Area 1 Area 0 Area 2 Area 1 Area 0 Area

21 OSPF Areas Area serves as backbone area and distributes routing information between attached areas. AS Areas Area Area Area An AS can be divided into smaller groups called areas LSA flooding can be constrained to an area, which effectively reduces the size of the link-state database All routers maintain an identical copy of the link-state database on a per-area basis

22 OSPF Routers Area border routers (ABRs) belong to Area and an attached area. Backbone routers have at least one link in OSPF Area AS Area Area Area ASBRs inject routing information from outside the OSPF domain. Internal routers have all OSPF links in the same area

23 OSPF Area Types Special stub area that allows external routes to be advertised from the area but not received from another area Intra-Area Routes Stub Area Does not carry external routes and cannot contain ASBRs Not-So-Stubby Area Interarea Routes (Summary Routes) Totally Stubby Area Stub area that receives only a default route from the backbone Backbone ( ) RIP External Routes BGP Default Route

24 Overview of the LSA Packet Types Router Links Type 1 Network Links Type 2 Describe the state and cost of the router s links (interfaces) to the area (Intra-area). Originated for multi-access segments with more than one attached router. Describe all routers attached to the specific segment. Originated by a designated router (DR). Summary Links Type 3 and Type 4 External Links Type 5 NSSA External Links Type 7 NSSA ABR Originated by ABRs. Describe networks in the AS but outside of area (interarea). Also describe the location of the ASBR. ASBR Originated by an ASBR. Describe external destination prefixes or a default route. ASBR Used by not-so-stubby areas to import external routes into a stub area

25 Test Your Knowledge Which of the recently discussed LSAs would you expect to find in each of the listed areas? Stub Area Not-So-Stubby Area Totally Stubby Area Backbone ( ) RIP BGP

26 Agenda: Open Shortest Path First Overview of OSPF Adjacency Formation and the DR Election OSPF Scalability Configuring and Monitoring OSPF Basic OSPF Troubleshooting

27 Junos OS OSPF Support The Junos OS supports OSPF version 2 and version 3, as well as a number of supporting features, such as: Stub, not-so-stubby, and totally stubby areas Authentication Summarization External prefix limits Graceful restart Bidirectional Forwarding Detection

28 Configuring OSPF [edit protocols] show ospf { area <area-id> { <area options>; interface <interface-name> { <interface options>; ospf3 { area <area-id> { <area options>; interface <interface-name> { <interface options>; Used for IPv4 routing environments Used for IPv4 or IPv6 routing environments

29 The Router ID OSPF uses the RID to identify the router from which a packet originated You can manually define the RID under the [edit routing-options] hierarchy [edit routing-options] user@r1# show router-id ; The RID is a 32-bit number in dotted quad notation. If you do not configure a RID, a non-127/8 IP address of the first interface to come online is used (typically lo0) If lo0 does not have a suitable address, the IP address associated with first hardware interface is used Note: We strongly recommend that you configure a RID to avoid unpredictable behavior if the interface addresses are changed

30 Case Study: Topology and Objectives Use the following topology as a guide to implement OSPF On R1, redistribute the /24 network and ensure that it is installed as an external OSPF route Use metrics to ensure that the path using the ge-0/0/1 interfaces within the backbone area is preferred ge-0/0/1 Area Area Area /30 ge-1/0/0 ge-0/0/3 ge-0/0/1 ge-0/0/1 ge-0/0/3 ge-1/0/ / /30 ge-0/0/ /30 ge-0/0/ /30 R1 - lo0/rid: R2 - lo0/rid: R3 - lo0/rid: R4 - lo0/rid:

31 Case Study: Configuring OSPF [edit protocols] show ASBR (Policy is defined and ospf { applied on the next slide.) area { interface ge-1/0/0.0; interface lo0.0; [edit protocols] user@r4# show ospf { area { interface ge-1/0/1.0; interface lo0.0; [edit protocols] user@r2# show ABRs ospf { area { interface ge-0/0/1.0; interface ge-0/0/2.0 { metric 100; interface lo0.0; area { interface ge-0/0/3.0; Increased metric for secondary path [edit protocols] user@r3# show ospf { area { interface ge-0/0/1.0; interface ge-0/0/2.0 { metric 100; interface lo0.0; area { interface ge-0/0/3.0;

32 Case Study: Redistributing the Route [edit policy-options] show policy-statement 2ospf { Redistribution policy is defined under term match-direct-route { [edit policy-options] hierarchy. from { protocol direct; route-filter /24 exact; then accept; [edit protocols] user@r1# show ospf { export 2ospf; area { interface ge-1/0/0.0; interface lo0.0; Redistribution policy is applied under [edit protocols ospf] hierarchy

33 Test Your Knowledge What configuration option allows R1 to inject the /24 prefix into OSPF as an internal OSPF route while prohibiting adjacency formation? [edit protocols] set ospf area 1 interface ge-0/0/1.0 passive Include the passive option for the interface ge-0/0/1 Area Area Area /30 ge-1/0/0 ge-0/0/3 ge-0/0/1 ge-0/0/1 ge-0/0/3 ge-1/0/ / /30 ge-0/0/ /30 ge-0/0/ /30 R1 - lo0/rid: R2 - lo0/rid: R3 - lo0/rid: R4 - lo0/rid:

34 Case Study: Monitoring OSPF (1 of 2) Use the show ospf neighbor command to display OSPF adjacency information show ospf neighbor Address Interface State ID Pri Dead ge-0/0/1.0 Full ge-0/0/2.0 Full ge-0/0/3.0 Full ge-0/0/1 Area Area Area /30 ge-1/0/0 ge-0/0/3 ge-0/0/1 ge-0/0/1 ge-0/0/3 ge-1/0/ / /30 ge-0/0/ /30 ge-0/0/ /30 R1 - lo0/rid: R2 - lo0/rid: R3 - lo0/rid: R4 - lo0/rid:

35 Case Study: Monitoring OSPF (2 of 2) Use show route commands to verify route entries and their selected paths show route /24 External prefix injected by R1 inet.0: 13 destinations, 13 routes (13 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both /24 *[OSPF/150] 02:37:46, metric 0, tag 0 > to via ge-0/0/3.0 user@r2> show route /30 inet.0: 13 destinations, 13 routes (13 active, 0 holddown, 0 hidden) + = Active Route, - = Last Active, * = Both /30 *[OSPF/10] 02:24:29, metric 2 > to via ge-0/0/1.0 Remote subnet connecting R3 and R4 is reachable through desired path

36 Other Key Monitoring Commands Additional show commands exist to provide detailed information on the operation of OSPF: show ospf interface show ospf route show ospf database show ospf statistics show ospf log

37 Displaying OSPF Interface Parameters Use the show ospf interface command to display OSPF interface parameters show ospf interface Interface State Area DR ID BDR ID Nbrs ge-0/0/1.0 BDR ge-0/0/2.0 DR lo0.0 DR ge-0/0/3.0 DR ge-0/0/1 Area ge-1/0/0 ge-0/0/3 ge-0/0/1 Area /30 ge-0/0/ / /30 ge-0/0/ /30 ge-0/0/2 R1 - lo0/rid: R2 - lo0/rid: R3 - lo0/rid:

38 Displaying OSPF Route Information Use the show ospf route command to display routes learned from, and advertised to, OSPF show ospf route Topology default Route Table: Prefix Path Route NH Metric NextHop Nexthop Type Type Type Interface addr/label Intra AS BR IP 1 ge-0/0/ Intra Area BR IP 1 ge-0/0/ /24 Ext2 Network IP 0 ge-0/0/ /30 Intra Network IP 1 ge-0/0/ /30 Intra Network IP 1 ge-0/0/ /30 Intra Network IP 100 ge-0/0/ /30 Inter Network IP 2 ge-0/0/ /32 Intra Network IP 1 ge-0/0/ /32 Intra Network IP 0 lo /32 Intra Network IP 1 ge-0/0/ /32 Inter Network IP 2 ge-0/0/ External prefix injected by R1 Metric for ge-0/0/2.0 interface was modified in earlier configuration example

39 Displaying the OSPF Link-State Database Use the show ospf database commands to view the OSPF link-state database show ospf database ABRs maintain a separate database for each OSPF area to which they are attached. OSPF database, Area Type ID Adv Rtr Seq Age Opt Cksum Len Router * x c x22 0x84ae 60 Router x x22 0x545e 60 Network x x22 0x43e3 32 Network x x22 0x38ed 32 Summary * x x22 0x4db7 28 Summary x x22 0xe9f8 28 Summary * x x22 0xa3bb 28 Summary x a x22 0x57ef 28 ASBRSum * x x22 0x93c9 28 OSPF database, Area Type ID Adv Rtr Seq Age Opt Cksum Len Router x x22 0x82c3 48 OSPF AS SCOPE link state database Type ID Adv Rtr Seq Age Opt Cksum Len Extern Worldwide 0x Education Services 96 0x22 0x374c Juniper Networks, Inc. All rights reserved

40 Displaying OSPF SPF-Related Information Use the show ospf log command to display OSPF SPF-related information show ospf log Last instance of each event type When Type Elapsed 04:28:24 SPF :28:24 Stub :28:24 Interarea :28:24 External :28:24 NSSA :28:24 Cleanup Maximum length of each event type When Type Elapsed 20:09:11 SPF Last 100 events When Type Elapsed 16:38:21 NSSA

41 Displaying OSPF Statistics Use the show ospf statistics command to view OSPF statistics show ospf statistics Packet type Total Last 5 seconds Sent Received Sent Received Hello DbD LSReq LSUpdate LSAck DBDs retransmitted : 0, last 5 seconds : 0 LSAs flooded : 40, last 5 seconds : 0 LSAs flooded high-prio : 10, last 5 seconds : 0 LSAs retransmitted : 0, last 5 seconds : 0 LSAs transmitted to nbr: 8, last 5 seconds : 0 LSAs requested : 2, last 5 seconds : 0 LSAs acknowledged : 39, last 5 seconds :

42 Agenda: Open Shortest Path First Overview of OSPF Adjacency Formation and the DR Election OSPF Scalability Configuring and Monitoring OSPF Basic OSPF Troubleshooting

43 OSPF Troubleshooting Tool Kit Primary troubleshooting tools for OSPF include traceoptions and CLI show commands Protocol traceoptions CLI show commands

44 Common Adjacency Problems Adjacency problems and checklist items include: Problem No neighbor detected Stuck in ExStart state Stuck in 2-way state Checklist Check physical and data link layer connectivity Check for mismatched IP subnet/mask, area number, area type, authentication, hello/dead interval, or network type Check MTU settings to ensure that they match Normal for DR-Other neighbor

45 Using Traceoptions Use traceoptions to identify adjacency formation issues; a sample configuration is shown: [edit protocols] user@r1# show ospf { traceoptions { file trace-ospf; flag error detail; flag event detail; area { interface ge-1/0/0.0; interface lo0.0; User-defined file-name and flag options. Include the detail option to generate additional details in the associated log file. Area ge-1/0/0 ge-0/0/3 R1 - lo0: R2 - lo0: /

46 Displaying the Log File Contents (1 of 3) Use the show log file-name command to display the contents of the traceoptions log file show log trace-ospf Oct 13 09:05: OSPF packet ignored: area mismatch ( ) from on intf ge-1/0/0.0 area Oct 13 09:05: OSPF rcvd Hello > (ge-1/0/0.0 IFL 73 area ) Oct 13 09:05: Version 2, length 44, ID , area Oct 13 09:05: checksum 0x8c5c, authtype 0 Oct 13 09:05: mask , hello_ivl 10, opts 0x2, prio 128 Oct 13 09:05: dead_ivl 40, DR , BDR Area According to the log file, R2 has the wrong OSPF area configured. ge-1/0/0 ge-0/0/3 R1 - lo0: R2 - lo0: /

47 Displaying the Log File Contents (2 of 3) Use the show log file-name command to display the contents of the traceoptions log file show ospf neighbor Address Interface State ID Pri Dead ge-0/0/3.0 ExStart show log trace-ospf May 19 02:17: OSPF packet ignored: MTU mismatch from on intf ge-0/0/3.0 area May 19 02:17: OSPF packet ignored: MTU mismatch from on intf ge-0/0/3.0 area Area ge-1/0/0 ge-0/0/3 R1 - lo0: R2 - lo0: /30.2 According to the log file, the MTU values on the Gigabit Ethernet interfaces do not match. This mismatch is a common cause of an adjacency stuck in the ExStart state

48 Displaying the Log File Contents (3 of 3) Use the show log file-name command to display the contents of the traceoptions log file show log trace-ospf May 19 02:15: OSPF hello from (IFL 70, area ) absorbed May 19 02:15: OSPF hello from (IFL 71, area ) absorbed [edit protocols ospf] show traceoptions { file trace-ospf; flag hello; Area According to the log file, hellos from R1 are being absorbed, indicating normal operation between these two neighbors. ge-1/0/0 ge-0/0/3 R1 - lo0: R2 - lo0: /

49 Viewing OSPF Error Counters Use the show ospf statistics command to view OSPF errors show ospf statistics Receive errors: 410 area mismatches 17 mtu mismatches 81 Hellos received with our router ID Use clear ospf statistics to refresh counters clear ospf statistics

50 Summary In this chapter, we: Explained the operations of OSPF Described the role of the designated router Listed and described OSPF area types Configured, monitored, and troubleshot OSPF

51 Review Questions 1. What is the purpose of OSPF LSAs? 2. What benefits can exist by segmenting a large single-area OSPF environment into multiple areas? 3. What is the difference between an ABR and an ASBR? 4. List some common OSPF area types and their functional considerations

52 Lab 3: Open Shortest Path First Configure and monitor OSPF

53 Worldwide Education Services

KillTest *KIJGT 3WCNKV[ $GVVGT 5GTXKEG Q&A NZZV ]]] QORRZKYZ IUS =K ULLKX LXKK [VJGZK YKX\OIK LUX UTK _KGX

$KillTest *KIJGT 3WCNKV[ $GVVGT 5GTXKEG Q&A NZZV ]]] QORRZKYZ IUS =K ULLKX LXKK [VJGZK YKX\OIK LUX UTK _KGX$ KillTest Q&A Exam : JN0-643 Title : Enterprise Routing and Switching, Professional (JNCIP-ENT) Version : Demo 1 / 10 1.Which connection method do OSPF routers use to communicate with each other? A. IP