RID Question

Hey, I came along this question and I was curious to why they say physical address is the right answer rather than logical. For some reason I thought that physical would be the right answer, but he also configured logical which which then lead me to believe that would be the right answer. I guess I thought that phyical is the highest RID until you configure logical interfaces, then logical would be the RID.

You work as network administrator at ****.
Your trainee is configuring a router with both physical and logical interfaces.
He asks you what factor determines the OSPF router ID.
What should you tell him?
A. The lowest network number of any interface.
B. The lowest IP address of any logical interface.
C. The lowest IP address of any physical interface.
D. The highest network number of any interface.
E. The highest IP address of any logical interface.
F. The highest IP address of any physical interface.

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Comments

2lazybutsmart

Logical interfaces preceed any physical ones when it comes to choosing the RID.

triplebenc

So why then, is F the correct answer? when i thought it should be E

2lazybutsmart

F cannot be the correct answer.

Loopback interfaces take precedence over physical interfaces. That's a rule. The reason Cisco did it that way is so that you have permanent stable RIDs for easier administration. Otherwise, when links go down, a new RID must be generated. And of course you know that a loopback interface never goes down.

triplebenc

Alright thanks, so it looks like the practice test was incorrect then. I sat and thought about that question for like 10 min. on how the heck they got F. Glad to know they were wrong.
Thanks

Gogousa

Be careful with the practice tests. Get them from a reliable source.
I don’t know which one are you using but there are a lot of practice tests out there that have the wrong answers at purpose.

Yankee

Loopbacks take precedence but not ANY virtual interface. A frame relay subinterface is virtual. A multilink bundle is virtual. There are many types of virtual interfaces.

Yankee

darkuser

http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fipr_c/ipcprt2/1cfospf.htm#wp1001369

cisco_trouble

What you are saying is that if there is a loopback and serial int, if the serial int has a higher ip it still takes the loopback ip? So its the loopback int highest ip under any circumstances? or is it the highest ip under all configured interfaces? hmm...