IGP Troubleshooting 3

IGP Troubleshooting Topics for the JNCIE-SP Exam IS-IS adjacency issues Understand what can cause IS-IS adjacency issues Understand how to troubleshoot IS-IS adjacency issues OSPF adjacency problems Understand what can cause OSPF adjacency issues Understand how to troubleshoot OSPF adjacency issues Other troubleshooting scenarios Routing loops Overloaded routers Route summarization issues

IS-IS Adjacency Problems Possible causes: Mismatched area IDs for Level 1 IS-IS adjacencies Duplicate system IDs Incorrect IP addressing Mismatched subnet masks do not affect IS-IS adjacencies Hello authentication mismatch LSP authentication problems do not affect IS-IS adjacencies Mismatched interface types Interfaces missing the family iso statement Interfaces that are physically down Incorrect IS-IS interface placement Low MTU setting—less than 1492 for protocol family ISO

OSPF Adjacency Problems Possible causes: Duplicate RIDs Mismatched subnet masks or incorrect IP addressing Authentication mismatches Mismatched interface types OSPF interface priority set to 0 on both sides Interfaces that are physically down Mismatched area types or area IDs Mismatched hello intervals and dead intervals Mismatched MTU settings Remember to examine OSPFv2 and OSPFv3 adjacencies

Troubleshooting Adjacency Issues Troubleshooting tools monitor traffic interface interface-name detail Quick and dirty Use the no-resolve option to remove the look up delay Traceoptions More specific but might cost time deciding which flags to use IS-IS: hello detail and error detail flags OSPF: hello detail and error detail flags Examine which interfaces are participating in the protocol IS-IS: show isis interface OSPF: show ospf interface and show ospf3 interface Adjacency states might give valuable clues

Troubleshooting Routing Loops What is a routing loop? Anytime a packet passes through a routing instance more than once Packets will loop until the TTL expires Typically occurs at points of route redistribution How to troubleshoot a routing loop traceroute Helps to determine where the routing loop is occurring Examine routing tables Once you have found the point at which the packet loops, the routing tables on the involved routers can give valuable information

An Overloaded Router What does it mean to have an overloaded router in IS-IS or OSPF? In OSPF, the router advertises the maximum metric for any routes that will cause the router to forward transit traffic In IS-IS, the router floods its locally generated LSP, to other IS-IS routers, with the overload bit set Be careful if the overload timeout statement is configured Bouncing the protocol will cause the router to become overloaded A router can be configured to be overloaded or can become overloaded If the prefix-export-limit statement is configured and the router exceeds that limit, it becomes overloaded

Route Summarization Issues IS-IS route leaking Examine route leaking polices for common issues Incorrect criteria: from protocol, from level, and to level Incorrect actions: reject instead of accept OSPF area-range statement restrict option blocks route propagation into the backbone area Ensure the area-range statement is applied at the correct hierarchy level Directly under the area stanza for Type 1 and 2 LSAs Directly under the nssa stanza for Type 7 LSAs

Task and Topology Task: R4 R3 R5 OSPF Area 0 ge-0/0/3 R1 R2 Task: The OSPFv2 adjacency between R1 and R2 is currently not operational. Ensure that the adjacency reaches the Full state.

What Now? What are the required components? Must you troubleshoot OSPFv2 and OSPFv3? No Only OSPFv2 adjacency establishment is required Which troubleshooting tools can you use? Examine OSPF adjacencies Adjacency states might provide valuable clues monitor traffic interface interface-name detail or traceoptions MTU problems Hello and dead intervals Mismatched subnet masks Others

Task Completion (1 of 3) Examine the OSPFv2 adjacency lab@R1> show ospf neighbor Address Interface State ID Pri Dead 172.27.0.13 ge-0/0/6.0 Full 172.27.255.3 128 18 172.27.0.2 ge-0/0/3.0 Exchange 172.27.255.2 128 22 lab@R2> show ospf neighbor 172.27.0.1 ge-0/0/3.0 ExStart 172.27.255.1 128 26 172.27.0.17 ge-0/0/2.0 Full 172.27.255.3 128 18 172.27.0.21 ge-0/0/5.0 Full 172.27.255.4 128 17 172.27.0.25 ge-0/0/6.0 Full 172.27.255.5 128 10

Task Completion (2 of 3) Monitor R1’s ge-0/0/3 interface lab@R1> monitor traffic interface ge-0/0/3 detail no-resolve Address resolution is OFF. Listening on ge-0/0/3, capture size 1514 bytes 17:26:41.350994 In IP (tos 0xc0, ttl 1, id 17971, offset 0, flags [none], proto: OSPF (89), length: 52) 172.27.0.2 > 224.0.0.5: OSPFv2, Database Description, length 32 Router-ID 172.27.255.2, Area 0.0.0.0, Authentication Type: none (0) Options [Opaque], DD Flags [Init, More, Master], MTU: 1486, Sequence: 0xac172c39 17:26:41.352069 Out IP (tos 0xc0, ttl 1, id 41177, offset 0, flags [none], proto: OSPF (89), length: 132) 172.27.0.1 > 224.0.0.5: OSPFv2, Database Description, length 112 Router-ID 172.27.255.1, Area 0.0.0.0, Authentication Type: none (0) Options [Opaque], DD Flags [none], MTU: 1500, Sequence: 0xac172c39 Advertising Router 172.27.255.1, seq 0x80000004, age 777s, length 28 Router LSA (1), LSA-ID: 172.27.255.1 Options: [Demand Circuit] ...

Task Completion (3 of 3) Examine and change the MTU setting on R2’s ge-0/0/3 interface [edit interfaces ge-0/0/3] lab@R2# run show interfaces ge-0/0/3 | match mtu Link-level type: Ethernet, MTU: 1500, Speed: 1000mbps, BPDU Error: None, Protocol inet, MTU: 1486 Protocol inet6, MTU: 1486 lab@R2# set mtu 1514 lab@R2# commit commit complete Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps, BPDU Error: None, Protocol inet, MTU: 1500 Protocol inet6, MTU: 1500

Task Verification Examine the OSPFv2 adjacency lab@R1> show ospf neighbor Address Interface State ID Pri Dead 172.27.0.13 ge-0/0/6.0 Full 172.27.255.3 128 18 172.27.0.2 ge-0/0/3.0 Full 172.27.255.2 128 22 lab@R2> show ospf neighbor 172.27.0.1 ge-0/0/3.0 Full 172.27.255.1 128 26 172.27.0.17 ge-0/0/2.0 Full 172.27.255.3 128 18 172.27.0.21 ge-0/0/5.0 Full 172.27.255.4 128 17 172.27.0.25 ge-0/0/6.0 Full 172.27.255.5 128 10

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