2-2 - Troubleshoot Core IGP Flashcards
1
Q
Why do most service providers tend to use OSPF or IS-IS as their IGP?
A
- EIGRP is Cisco proprietary and may hinder interoperability with other vendors.
- MPLS TE requires the help of a link-state protocol, and EIGRP is a hybrid distance vector protocol.
2
Q
Describe the overall operation of OSPF.
A
- upon initialization, or due to a change in routing info, the router generates a link-state advertisement (LSA). This is a collection of all link states on the router.
- all routers exchange link states by flooding. Each router that receives a link-state update stores a copy in its link-state database (LSDB) and then propagates the update to other routers.
- After the database of each router is complete, the router calculates the shortest path tree to all destinations, using the Dijkstra algorithm. The destinations, associated cost, and next-hop to reach those destinations form the IP routing table
- If no changes in OSPF network occur, OSPF should be quiet.
3
Q
T/F: All routers within an area have different LSDBs.
A
False
4
Q
T/F: Flooding and calculation of Dijkstra’s algorithm on a router is limited to links within an area.
A
True
5
Q
Why do modern networks typically use single-area designs?
A
Modern networks typically use single-area designs since they allow for simplified MPLS TE designs and newer hardware capabilities make CPU power and memory resources less of a concern than they were in the past.
6
Q
Describe the following OSPF area type: backbone area
A
- carries all the routing info
- all other areas must directly connect to the backbone area
- contiguious area
7
Q
Describe the following OSPF area type: regular area
A
- nonbackbone areas that directly connect to area 0
8
Q
Describe the following OSPF area type: stubby area
A
- areas that do not originate or receive any external routes
9
Q
Describe the following OSPF area type: totally stubby area
A
- areas do not originate (redistribution from other protocols) or receive any external routes or summaries (only the default route)
10
Q
Describe the following OSPF area type: not-so-stubby area (NSSA)
A
- can originate external routes (redistribution from other protocols), but they do not receive them from other OSPF areas
11
Q
Describe the following OSPF area type: totally not-so-stubby area (Totally NSSA)
A
- can originate external routes (redistribution from other protocols), but they do not receive them from other areas
- these areas also do not receive summaries (only the default route)
12
Q
Describe the following OSPF router type: internal router
A
- routers with all their interfaces configured in the same area
13
Q
Describe the following OSPF router type: backbone router
A
- internal routers within area 0
14
Q
Describe the following OSPF router type: ABR
A
- area border router
- belongs to multiple areas and connects these areas to the backbone area.
- ideal design: each ABR connect to two areas only. the backbone area and another area (with 3 areas being the upper limit)
15
Q
Describe the following OSPF router type: ASBR
A
- autonomous system boundary router
- connects the OSPF area to a different routing administration (e.g. BGP, EIGRP, etc.)
- the point where external routes can be redistributed into OSPF
16
Q
IOS-XR command:
router ospf [process ID]
A
- enters OSPF router configuration mode
- process ID is only locally significant
17
Q
IOS-XR command:
router ospf [process ID] area [area #] interface [interface]
A
- enters the area subconfig and enables an interface for OSPF in that area
18
Q
IOS/IOS-XE command:
router ospf [process ID]
A
- enters OSPF router configuration mode
- process ID is only locally significant
19
Q
IOS/IOS-XE command:
network [network address] [wildcard mask] area [area #]
A
- within the OSPF subconfig, this command is used to match on networks in order to enable associated interfaces for OSPF within the specified area
- this is a legacy method for configuring this
20
Q
IOS/IOS-XE command:
ip ospf [OSPF process id] area [area #]
A
- within interface subconfig, this command is used to enable OSPF on the interface in the specified area
- this is a new way of configuring it, introduced in IOS 12.3(11)T and all IOS-XE releases
21
Q
Describe what this OSPF route abbreviation in the RIB represents:
O
A
- OSPF intraarea route
- networks within the are of the router
- advertised by means of type 1 (router) and type 2 (network) LSAs
22
Q
Describe what this OSPF route abbreviation in the RIB represents:
O IA
A
- OSPF interarea route (summary)
- networks outside of the area of the router but within the OSPF autonomous system
- advertised by means of summary (type 3) and summary ASBR (type 4) LSAs
23
Q
Describe what this OSPF route abbreviation in the RIB represents:
O E1
A
- OSPF external type 1 route
- networks outside of the OSPF autonomous system of the router
- advertised by means of external LSAs (LSA type 5)
- adds the costs on links inside the OSPF network to the cost of the external link (more accurate)
24
Q
Describe what this OSPF route abbreviation in the RIB represents:
O E2
A
- OSPF external type 2 route
- networks outside of the OSPF autonomous system of the router
- advertised by means of external LSAs (LSA type 5)
- has the cost of the external link no matter how many links it passes through in the internal network (less accurate)
25
IOS-XR Command:
show ospf
- verify the OSPF routing protocol
26
IOS-XR Command:
show ospf interface
- verify OSPF interface information
27
IOS-XR Command:
show ospf neighbor
- verify OSPF neighbors
28
IOS-XR Command:
show route ospf
- verify OSPF routes learned by the router in the IP routing table
29
IOS-XR Command:
show protocols
- verify configured IP routing protocol processes
30
IOS-XR Command:
show ospf database
- verify OSPF LSDB
31
IOS/IOS-XE command:
show ip ospf
- verify the OSPF routing protocol
32
IOS/IOS-XE command:
show ip ospf interface
- verify OSPF interface information
33
IOS/IOS-XE command:
show ip ospf neighbor
- verify OSPF neighbors
34
IOS/IOS-XE command:
show ip route ospf
- verify OSPF routes learned by the router in the IP routing table
35
IOS/IOS-XE command:
show ip protocols
- verify configured IP routing protocol processes
36
IOS/IOS-XE command:
show ip ospf database
- verify OSPF LSDB
37
What OSI Layer is IS-IS implemented at?
Layer 2 (Data Link Layer)
38
Name the RFC and ISO standards for Integrated IS-IS.
RFC 1195 and ISO 10589
39
T/F: Level 1 routing occurs across multiple IS-IS areas.
False
40
T/F: Level 1 and Level 2 adjacencies can from between routers in the same area.
True
41
T/F: Only level 2 adjacencies can form between routers in different areas
True
42
Describe a Level 1 IS-IS router.
routes within an IS-IS area
43
Describe a Level 2 IS-IS router.
Learns the locations of Level 1 routing areas and builds an inter-area routing table.
44
IOS-XR Command:
router isis [process ID]
- enters IS-IS router configuration mode
- process ID is only locally significant
45
IOS-XR Command:
net [NET value]
- within the ISIS subconfig mode, configure the Network Entity Title (NET) for this intermediate system
46
IOS-XR Command:
address-family ipv4 unicast
- enter the IPv4 AF subconfig mode for ISIS
47
IOS/IOS-XE Command:
router isis [process ID]
- enters IS-IS router configuration mode
- process ID is only locally significant
48
IOS/IOS-XE Command:
net [NET value]
- within the ISIS subconfig mode, configure the Network Entity Title (NET) for this intermediate system]
49
IOS/IOS-XE Command:
ip router isis [process ID]
- in interface subconfig mode, this command enables ISIS on the interface
50
IOS-XR Command:
show isis interface
- displays the interfaces that you enable for IS-IS
51
IOS-XR Command:
show isis neighbors
- displays the IS-IS neighbors that the system recognizes
52
IOS-XR Command:
show isis topology
- displays the Level 1 and Level 2 topology tables, which show the least-cost IS-IS paths to the intermediate systems
53
IOS-XR Command:
show isis database
- displays the contents of the IS-IS LSDB
54
IOS-XR Command:
clear isis process
- to force IS-IS to refresh its LSDB and recalculate all routes
55
IOS-XR Command:
show isis database [LSP_ID] detail
- displays the detailed contents of each IS-IS LSDB and the prefixes that advertise for a specified routing process
56
IOS/IOS-XE Command:
show ip protocols
- show IPv4 routing protocol processes that are configured and running on the router
57
IOS/IOS-XE Command:
show ip route isis
- show the routing table entries that were learned via ISIS
58
IOS/IOS-XE Command:
show isis neighbors
- displays the IS-IS neighbors that the system recognizes
59
IOS/IOS-XE Command:
show isis topology
- displays the Level 1 and Level 2 topology tables, which show the least-cost IS-IS paths to the intermediate systems
60
IOS/IOS-XE Command:
show isis database
- displays the contents of the IS-IS LSDB
61
IOS/IOS-XE Command:
clear isis
- to force IS-IS to refresh its LSDB and recalculate all routes (you can use an asterisk [*] to clear all IS-IS processes)
62
IOS/IOS-XE Command:
show isis database [LSP_ID] detail
- displays the detailed contents of each IS-IS LSDB and the prefixes that advertise for a specified routing process
63
Describe what this IS-IS route abbreviation in the RIB represents:
i L1
- IS-IS learned, Level 1 route
64
Describe what this IS-IS route abbreviation in the RIB represents:
i L2
- IS-IS learned, Level 2 route
65
Describe what this IS-IS route abbreviation in the RIB represents:
i su
- IS-IS learned, summary route
