1. IGP Troubleshooting 3

2. 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

3. 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

4. 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

5. 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

6. 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

7. 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

8. 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

9. 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.

10. 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

11. Task Completion (1 of 3) Examine the OSPFv2 adjacency
show ospf neighbor
Address Interface State ID Pri Dead
ge-0/0/ Full
ge-0/0/ Exchange
show ospf neighbor
ge-0/0/ ExStart
ge-0/0/ Full
ge-0/0/ Full
ge-0/0/ Full

12. Task Completion (2 of 3) Monitor R1’s ge-0/0/3 interface
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: In IP (tos 0xc0, ttl 1, id 17971, offset 0, flags [none], proto: OSPF (89), length: 52) > : OSPFv2, Database Description, length 32
Router-ID , Area , Authentication Type: none (0)
Options [Opaque], DD Flags [Init, More, Master], MTU: 1486, Sequence: 0xac172c39
17:26: Out IP (tos 0xc0, ttl 1, id 41177, offset 0, flags [none], proto: OSPF (89), length: 132) > : OSPFv2, Database Description, length 112
Router-ID , Area , Authentication Type: none (0)
Options [Opaque], DD Flags [none], MTU: 1500, Sequence: 0xac172c39
Advertising Router , seq 0x , age 777s, length 28
Router LSA (1), LSA-ID:
Options: [Demand Circuit]
...

13. 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]
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
set mtu 1514
commit
commit complete
Link-level type: Ethernet, MTU: 1514, Speed: 1000mbps, BPDU Error: None,
Protocol inet, MTU: 1500
Protocol inet6, MTU: 1500

14. Task Verification Examine the OSPFv2 adjacency
show ospf neighbor
Address Interface State ID Pri Dead
ge-0/0/ Full
ge-0/0/ Full
show ospf neighbor
ge-0/0/ Full
ge-0/0/ Full
ge-0/0/ Full
ge-0/0/ Full

15. 3