Section 1.5 - OSPFv2 Summarization

Question 1

T/F) Only ABRs can summarize internal routes

Answer 1

True

Question 2

What type of LSAs can ABRs summarize?

Answer 2

Type 3 LSAs

Question 3

What type of LSAs can ASBRs summarize?

Answer 3

Type 5 LSAs

Question 4

What is the cost of a summary route when RFC 1583 (default) is in effect?

Answer 4

The minimum cost value (of any one summarized component route) becomes the cost of the summary route

Question 5

What is the cost of a summary route when RFC 2328 (non-default) is in effect?

Answer 5

The maximum cost (of any one summarized component route) becomes the cost of the summary route

Question 6

What is the IOS/IOS-XE command to enable RFC 2328 for determining the cost of OSPF summary routes?

Answer 6

router ospf 1
no compatible rfc1583

Question 7

T/F) A good rule of thumb is to ensure that network numbers in areas are assigned contiguously.

Answer 7

True.

This ensures that these addresses can be summarized into a minimal number of summary addresses.

Question 8

What is the IOS-XR command to summarize routes at an area boundary (ABR)?

Answer 8

conf t
router ospf 1
area 1
range 192.168.0.0/16

Question 9

What is the IOS/IOS-XE command to summarize routes at an area boundary (ABR)?

Answer 9

conf t
router ospf 1
area 1 range 192.168.0.0 255.255.0.0

Question 10

T/F) Summarization of external routes cannot be done by the ABR in NSSAs.

Answer 10

False.

Summarization of external routes can be done by the ABR in NSSAs as well, where the ABR creates type 5 summary routes from type 7 external routes.

Question 11

T/F) A summary route to Null0 is created automatically for each summary range.

Answer 11

True.

This helps avoid possible routing loops.

Question 12

What are the OSPF external route cost types?

Answer 12

E1 - includes the original external cost PLUS total internal cost
E2 - cost at the point of redistribution remains the same throughout the rest of the OSPF domain

Question 13

What is the IOS-XR command to summarize routes at an ASBR boundary?

Answer 13

conf t
router ospf 1
summary-prefix 10.10.0.0 255.255.0.0

Question 14

What is the IOS/IOS-XE command to summarize routes at an ASBR boundary?

Answer 14

conf t
router ospf 1
summary-address 10.10.0.0 255.255.0.0 no-advertise

*The no-advertise keyword filters out the prefixes that are within a summary range.

Question 15

What are some characteristics of inter-area summarization (on ABR)?

Answer 15

• If using areas, you should use summarization if the addressing plan permits it
• Summarizing from areas limits routing table size and prevents unnecessary LSA flooding upon changes in areas
• Summarizing toward areas further reduces the routing table size in all areas
• Summarization breaks MPLS Label Switched Paths (LSPs), which will break MPLS-based services.

Question 16

What are some characteristics of inter-domain summarization (on ASBR)

Answer 16

• If redistributing into OSPF, you should also use summarization if the addressing plan permits it.
• Summarizing from external domains limits routing table size and prevents unnecessary flooding of external LSAs that propagate through the OSPF domain (backbone and regular areas) and cannot be filtered.

Question 17

Which Cisco IOS-XR command would you use to summarize routes into Area 0 from the ABR?

A) summary-address
B) network
C) summary-prefix
D) range

Answer 17

D