350-401 question 59: Refer to the exhibit. Which command, when applied on the Atlanta ro…

Q54Network Assurance

Refer to the exhibit. Which command, when applied on the Atlanta router, reduces Type 3 LSA flooding into the backbone area and summarizes the inter-area routes on the Dallas router?

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OSPF is a link state routing protocol that works on the concept of areas. All areas must have the same LSDB (link state database); therefore OSPF summarization can only be done on the border routers, i.e. on ABR (Area border router) and ASBR (Autonomous system boundary router). In this document we discussed route summarization between the areas. Background: Summarization between areas can be done on ABR by using a single command under OSPF process: area [area-id] range [ ip-address ] [mask ] [advertise | not-advertise |cost {cost}] A) area-id= Identifier of the area about which routes are to be summarized B) [ ip-address ] [mask]= Summary route to be advertise in areas https://community.cisco.com/t5/networking-documents/ospf-inter-area-route-summarization/ta-p/3145113

D! 192.168.0.0/24 192.168.2.0/24 192.168.3.0/24 192.168.4.0/24 128 64 32 16 8 4 2 1 =255 192.168.0.0 11000000 10101000 00000-000 00000000 192.168.1.0 11000000 10101000 00000-001 00000000 192.168.2.0 11000000 10101000 00000-010 00000000 192.168.3.0 11000000 10101000 00000-011 00000000 192.168.0.0 11000000 10101000 000000-11 00000000 192.168.0.0/22

B and D would both do the job. But D is a closer exact match for those subnets, while B would allow those four subnets plus another four. I assume they're looking for answer D because it matches the subnet list exactly.

D 3

Selected Answer: D We need to configure a summarized route for Area 1 information and advertise it to the Dallas router to reduce LSA type 3 messages. Atlanta(config)# router ospf <process ID> Atlanta (config-router)# area 1 range 192.168.0.0 255.255.248.0 Network 192.168.0.0/22 with a SM 255.255.252.0 has the following: Network IP: 192.168.0.0 First IP: 192.168.0.1 Last IP: 192.168.3.254 Broadcast IP: 192.168.3.255 It encompasses all the IP ranges for all the individual routes being advertised by Area 1 routers.

D is good since it summarizes the best those 4 subnets 192.168.0/1/2/3.X

This is route summarization and the given answer is correct

192.168.0.0/24 192.168.1.0/24 192.168.2.0/24 192.168.3.0/24 128 64 32 16 8 4 2 1 =255 192.168.0.0 11000000 10101000 00000-000 00000000 192.168.1.0 11000000 10101000 00000-001 00000000 192.168.2.0 11000000 10101000 00000-010 00000000 192.168.3.0 11000000 10101000 00000-011 00000000 192.168.0.0 11000000 10101000 000000-11 00000000 192.168.0.0/22

D 2

Selected Answer: D #area 1 range 192.168.0.0 255.255.252.0 it means it advertises the summary route FROM area 1 TO -> area 0 on the Dallas router, it will look like -> 192.168.0.0/22 (one instead four routes/24)

Correct answer is D, I was wrong, this is a range not a filter, I missed the key word, range is applied to source of the LSA, my apology.

Correct answer is D.

B would break Area 0

+ this command adds the summary route to GRT next-hop NULL0: cisco_R3#show ip route ospf | b Gate Gateway of last resort is 2.2.2.2 to network 0.0.0.0 55.0.0.0/8 is variably subnetted, 2 subnets, 2 masks O 55.0.0.0/18 is a summary, 00:31:04, Null0 <<<<<<<<<<<<<<<<<<< O 55.0.0.0/24 [110/101] via 10.111.10.2, 00:31:04, Ethernet0/0.50 cisco_R3#show runn | s ospf router ospf 1 router-id 3.3.3.3 auto-cost reference-bandwidth 1000 area 22 range 55.0.0.0 255.255.192.0 <<<<<<<<<<<<<<<<<<<<<< area 22 filter-list prefix PL_3 in passive-interface default no passive-interface Ethernet0/0.10 no passive-interface Ethernet0/0.50 network 0.0.0.0 255.255.255.255 area 0 bfd all-interfaces cisco_R3#

i'm not really sure that it would, since you'd have a more specific match as a connected route.. but that is specific to this particular topology

It might not break area 0, but the summarization would still include the subnet that's in area 0: 192.168.4.0/24 (255.255.248.0 would include 192.168.0-7.0), so at the very least, bad practice.

B 1

Selected Answer: B We need to configure a summarized route for Area 1 information and advertise it to the Dallas router to reduce LSA type 3 messages. Atlanta(config)# router ospf <process ID> Atlanta (config-router)# area 1 range 192.168.0.0 255.255.248.0 Network 192.168.0.0/22 with a SM 255.255.248.0 has the following: Network IP: 192.168.0.0 First IP: 192.168.0.1 Last IP: 192.168.3.254 Broadcast IP: 192.168.3.255 It encompasses all the IP ranges for all the individual routes being advertised by Area 1 routers.

Note: OSFP can summarize routes only on ABRs and ASBRs

Correction: The answer is D because SM for /22 IP address is 255.255.248.0 The rest of the information above is correct.

Correction: SM for /22 IP address is 255.255.252.0 **

area 1 range 192.168.0.0 255.255.252.0 **

Dallas is in Area 0, it's area 0 which is the backbone and prefixes that need to be summarized are in area 1, so it's 1->0, LSA Type three summarization should be applied on ABR Atlanta indicating number of destination area: area 0, therefore neither B or D are correct