confused about link vs. interface

I am studying for CCNA 101-100 and am confused about the following question:

Question: What OSPF features have been updated for IPv6?
A. It uses a 64-bit number instead of an Internet Protocol version 4, or IPv4 address for the router ID
B. Enabled per-link, not per-network
C. Adjacencies and next-hop attributes use the router ID as global addresses
D. IPv6 is used for transport of the link-state advertisement, or LSA

Correct answer is B and D.

My question is "Is a link the same thing as an interface or just referring to the physical part of the interface".

Plugging away....

-Benny

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carterw65

In my understanding a link is the connection between two devices. An interface is just what you use on each device to form the link and can either be a physical interface or, in the case of sub-interfaces, a virtual interface.

koz24

Hey Benny,

They are pulling the question from RFC 5340. Here's what it says:

IPv6 uses the term "link" to indicate "a communication facility or medium over which nodes can communicate at the link layer" (URL="https://tools.ietf.org/html/rfc5340#ref-IPV6"]IPV6[/URL). "Interfaces" connect to links. Multiple IPv6 subnets can be assigned to a single link, and two nodes can talk directly over a single link, even if they do not share a common IPv6 subnet (IPv6 prefix). For this reason, OSPF for IPv6 runs per-link instead of the IPv4 behavior of per-IP-subnet. The terms "network" and "subnet" used in the IPv4 OSPF specification (URL="https://tools.ietf.org/html/rfc5340#ref-OSPFV2"]OSPFV2[/URL) should generally be replaced by link. Likewise, an OSPF interface now connects to a link instead of an IP subnet. This change affects the receiving of OSPF protocol packets, the contents of Hello packets, and the contents of network-LSAs.

https://tools.ietf.org/html/rfc5340#section-2.1

Hope that helps!

carterw65

koz24 wrote: »

Hey Benny,

They are pulling the question from RFC 5340. Here's what it says:

https://tools.ietf.org/html/rfc5340#section-2.1

Hope that helps!

koz,

How in the world did you know that was there? Were you just happening to be reading it at the time? I haven't memorized any of the RFCs.

koz24

carterw65 wrote: »

koz,

How in the world did you know that was there? Were you just happening to be reading it at the time? I haven't memorized any of the RFCs.

I just remember reading that particular RFC when I was studying OSPF. I don't remember their #s by heart but I have a general idea of what's in them for the core topics. Some of the exams love RFC trivia so it's a good idea to get familiar with the important ones. I think I just went by the blueprint and looked up relevant RFCs.