OSPF Questions 3

Thank you very much

answer to Q7 is wrong:
Default ref-BW is 100Mbps, so changing it to ref-BW 100Mbps will change nothing!
Answer A

@keesie

You are right, at least in IOS version Version 12.4(13b) the value in the “auto-cost reference-bandwidth value” is in Mbps not kbps.

“Question 7
Note: The default reference bandwidth for OSPF is 10^8 bps or 100Mpbs so the “auto-cost reference-bandwidth 100” is in fact the default value so answer A may be a correct answer.”

Yeah, 100 is already the default, so I would say ‘A’ is definitely the correct answer. The explanation says this and multiple people calling it out… please update the PDF if this is the agreed answer.

Hello Everyone,
Yes for Question 7 your theory is correct but think if there was some other reference BW before and now he changed to “auto-cost reference-bandwidth 100”. Then obviously the statement “The data path changes for all links” i.e C will be the answer.

Q6
IS-IS is a “Link-State” routing protokoll
OSPF is also an “Link-State” routing protokoll
EIGRP is an hybrid but CISCO say this is an “distance vector” protocol

https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/13669-1.html#igrp

i think OSPF is the right anwser.

on question 7, notice the question never mentions ospf, C is the correct answer. We only are assuming they are talking about OSPF because the question is in the OSPF section of the PDF. But it does NOT actually say OSPF anywhere.

er nvm, just dawned on me that’s an OSPF only command. hmm so A could be right

Question 7

The answer is all paths changes for all links. Since you only are coding in the value (although default) on ONE router in the network. Whats to say the other routers on the network are not configured on defaults (including this one). By changing one router only you will get strange routing updates if the configurations do not match the other routers on the network.
https://supportforums.cisco.com/t5/network-infrastructure-documents/how-to-configure-ospf-cost/ta-p/3133153

what is the answer, C or A? in explanation, the said answer is A.

Question 7

If you configure one router in your network with the auto-cost reference-bandwidth 100 command, which effect on the data path is true?
A. The data path remains the same for all links
B. The data path changes for 10Mbps links only
C. The data path changes for all links
D. The data path changes for 10Gbps links only

Answer: C

Explanation

This command affects all the OSPF costs on the local router as all links are recalculated with formula: cost = reference-bandwidth (in Mbps) / interface bandwidth

Note: The default reference bandwidth for OSPF is 10^8 bps or 100Mpbs so the “auto-cost reference-bandwidth 100” is in fact the default value so answer A may be a correct answer.

Thanks.

Q3 area id , if u type subnet mask instead of wildcaed ios bu default convert it to wildcard

one approach for migrating from one routing protocol to another is to make sure new routing protocol has higher AD, ….
Q6 internal bgp and rip

About Q6. The migration to RIP is meaningless. I think we have just an incomplete question.

Could anyone explain Q2? I don’t understand two issue there.
1. The routers in the area and their priority doesn’t matters for Router ID. Why it mentioned in question?
2. With case in the absence of a loopback interface the OSPF process uses the highest ip address of nonloopback interface. Does it matter physical or logical interface have a highest ip?

Q2 is an incorrect question, I guess. I tested it in UNL – it doesn’t matter there is physical or logical interface, because a router just select highest IP from any available interface (I didn’t configure loopback in this lab).

I have tested Q7 in UNL:
R1(config)#router ospf 1
R1(config-router)#au
R1(config-router)#auto-cost reference-bandwidth 100
R1(config-router)#auto-cost reference-bandwidth 1000
% OSPF: Reference bandwidth is changed.
Please ensure reference bandwidth is consistent across all routers.

As you can see, nothing happens after implementing first command. I think correct answer is A: “The data path remains the same for all links.”

P.S. By default, Reference-Bandwidth is 100 (100, 000 in kbps) and SVI BW is 1000000 Kbit, so we need auto-cost reference-bandwidth 10000 to see meaningful changes. In that case the cost of 1Gb links will be 10 (10,000,000 / 1,000,000 = 10).

Real and effective, can be used as a reference, very effective, I hope to help you.
W w

w.cc iedumps.xyz/ccie_rs.php?ut m_source=bbs&utm_medium=bbs

he default reference bandwidth for OSPF is 10^8 bps or 100Mbit. Answer A.

The complete Q6 is:
If you want to migrate an IS-IS network to another routing protocol with lower AD, which one would you take?
So OSPF would be right and I think I had to choose two, so (internal) EIGRP makes most sense for replace IS-IS.

Q6? Answer: F
The first step in migration by AD is to turn on the new protocol, but make sure that it has a higher AD than the existing routing protocol so it is not preferred.
http://www.ciscopress.com/articles/article.asp?p=1763921&seqNum=4

Q2

hmm .. it takes the highest ip of any interface.. at least lo interfaces are prefered… so it will take the highest ip at lo intefaces right? so lo ist a logical interface right? — may be its D???

@el_recepo

you are correct, the answer should be D

@el_recepo

Actually I stand corrected, the answer should be B because the questions specifically stated “in the absence of loopback interface”, so the highest physical interface IP would’ve been chosen

Question 7

According to cisco the command “auto-cost reference-bandwidth 100” considers that you set the value 100 in Gbps (default), if you do not specify in the end of the command “Mbps” or “Gbps”

https://www.cisco.com/c/m/en_us/techdoc/dc/reference/cli/nxos/commands/ospf/auto-cost-ospf.html

That means that data path changes for all links… So C is correct.