instructor gave me sample question without answers for the final tomorrow and few of them are multi which I am a bit confused and I surfed online and read his notes over and I came into a conclusion for the multi. I'm just wondering if someone can confirm with me
What is the purpose of an LSA ?
a. To construct a topological database
b. To specify the cost to reach a destination
c. To determine the best path to a destination
d. To verify that a neighbor is still functioning
LSA's only purpose is to advertise neighbors immediately whenever there's a change to the topology table.
I would think that the answer a. makes sense to me.
LSA can be either (1) a requesting packet or (2) an update packet.
There are several types of LSAs out there (while we typically use maybe 3 of them commonly):
Type 1: router LSA. A router sends this to describe neighbors and its own interfaces.
Type 2: network LSA. For broadcast networks only; this LSA is flooded by the DR and lists OSPF-speaking routers on the network.
Type 3: network summary LSA. Sent by an ASBR to advertise networks reachable through it. A stub area router will also use this for the default route.
Type 4: ASBR-summary LSA. Sent by ASBR, but only internally. This describes to the others how to get to the ASBR itself, and uses only internal metrics.
Type 5: AS-external LSA. Used to describe external routes to internal areas. Can be used to advertise “this is the way to the Internet” (or some subset of).
Type 6: Group summary. Used in multicast (MOSPF). Ignore this.
Type 7: NSSA area import.
Oh I thought LSA is just giving an update packet instead of requesting because I thought requesting is during the stage where one router is newly installed and starting the finding neighbor starting from hello stage, dbd, lsr, lsu then lsa...
There's something new to learn everyday ^_^
By the way for this question I wonder why is it false
"An Ethernet network has only one router connected to it. This router will become the DR."
I thought a network will have a DR for sure....well it's not mentioned from the instructor or the notes he gave but that's just my assumption that it should be true but actually it's false.
I just realized I have two more questions that I'm not sure of...
One of the Problems with Link State Algorithms is:
a. Too Costly
b. Too Fast
c. Too Hard to Configure
d. Too Much Overhead for Large number of Routers
I haven't done any of the works on hands yet so not sure if it's too hard to configure so I would go for (D) as the answer but I thought Areas is the way to control too much overhead for large number of routers. So...I'm really not sure about this one...anyone might give me a hand?
On an Ethernet segment, link state routing protocols, such as ospf, exchange link information via :
a. ESP
b. Broadcasts
c. Unicast
d. Multicast
e. IPX
f. Frame Relay
g. ATM
I know that broadcast is just for the starting and the rest should be just unicast but this question asked about exchanging link information but is it a new ospf installed trying to exchange information or one that's already installed. Or I am just over thinking that unicast should be the answer hehe...
Assuming that d) implies that too many routers on the network means too big of the network, then the answer is (d) (too much overhead).
Why? Link State Algorithm is known with deficiencies such as: when the network is too big, it will become very time-consuming(running algorithm, exchanging info, etc.)
**sorry, will look into 2nd q later (kids crying).
for Ethernet network (broadcast-based), because of the existence of both a DR (designated router) and possibly a BDR(backup designated router), to maintain the convergence table and proper adjacency relationships with other routers.
The DR sends multicast packets to all routers that it has established adjacencies with (hello packets).
If the DR fails, it is the BDR that sends multicasts to specific routers.
So, my strong suspicion to your 2nd question is "multicast"...
for Ethernet network (broadcast-based), because of the existence of both a DR (designated router) an ...
Quest 發表於 2012-4-7 11:01
hehe that's what I wrote for both of my answers....and omg >.<' both of those questions popped up in the final last week....I won't know the result of each question but hopefully I did alrigh t...Quest...thanks for helping out
發表於 2012-4-4 20:21
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