My exam doubts

[komalthecoolk]

I thought I was well prepared but I'm gtting pounded in the pass4sure exams. I guess I under estimated the exam. Anyways., I have a few doubts that I want to ask if somebody can plz help me out with that. I got my exam in 2 days, so kindly help me out.

1) In the attachment in this post., can somebody plz tell me the answers to that question ? I've been getting it all wrong.

2) What is the use of "default-information originate". What does it do ?

3) What is a stub network ?

4) In framerelay what is the diff between point-to-point connections and multipoint connections.., a little detailed plz.

[komalthecoolk]

"access-list 101 deny tcp 5.1.1.10 0.0.0.0 5.1.3.0 0.0.0.255 eq telnet"

This ACL blocks telnet from 5.1.1.10 to 5.1.3.0 network.., but does it block telnet from 5.1.3.0 to 5.1.1.10 too ???

Somebody plzzz answer........,

[Visio]

1 ATTACHMENT SOLUTION

List number = 128
The acl statement is asking for a port and we know that only extended access lists support port numbers. Extended acl use numbers 100-199 or 2000 and 2699

Address = 64

172.16.5.118/26
255.255.255.192 – Subnet mask
2^10 = 1024 Subnets
2^6 – 2 = 62 Hosts
Valid Subnets = 256-192 = 64
The question says that all host in the same subnet containing 172.16.5.118 have to be denied. Our ip comes in the second subnet , hence the network address used will be 172.16.5.64



Wildcard Mask = 63
IP address is 172.16.5.118/26
There fore subnet is 255.255.255.192 ( because cidr is 26, default class B subnet is 255.255.0.0/16. So here we have 26-16=10 .. Hence 10 bits have to be turned on from left to right. So we get 255.255.11111111.11000000 which is nothing but 255.255.255.192)

Now to calculate the wildcard mask .. there is a simple math. Subtract the subnet mask from 255.255.255.255
Here our subnet mask is 255.255.255.192
Therefore our wildcard mask is 0.0.0.63
0.0.0.63 = 00000000.00000000.00000000.00111111
This means only the first 26 bits of the ip address must match.

Port = 23
23 is the telnet port

2. “default-information originate” causes an ASBR ( Autonomous System Border Router) to redistribute a default route into the OSPF area


3. Stub networks are OSPF networks with only one OSPF router attached. Stub networks receive data packets destined only for the stub network itself.


4. Frame relay uses Virtual Circuits (VCs) to establish connections .


In a point to point connection every device is linked to another device using a single logical network connection. Meaning only 2 devices share the same layer 3 network address structure, all other communication must be routed between the VCs.


In a point to multipoint connection, multiple VCs share the same layer 3 addressing structure. When a packet is sent to one VC on the network, it is sent to all VCs that are a part of the network. The packet doesn’t get repeated over logical ports but it gets routed to the network address that is shared by the VCs

[komalthecoolk]

@ Vijay: thanks a lot 4 the answers man., that really helps !! I'm sure a few more ppl will also be benefiting from this discussion.

My next doubt:

-- A VTP client doesnt save the vtp configuration in the NVRAM, but when it is running, does it save it in the running-config (RAM) ?

-- In access lists.., when we first block all IP traffic and in the next statement permit TCP or UDP traffic ( i know this is in the wrong order) will the TCP and UDP traffic still be permitted ? Are they independent of IP traffic ?

thank you :)

[nikzadr]

The Access list will stop the Telnet traffice in one direction but telnet protocol needs 2-way communication so neither of the hosts can create a telnet connection to the other one

[komalthecoolk]

Originally Posted by nikzadr

The Access list will stop the Telnet traffice in one direction but telnet protocol needs 2-way communication so neither of the hosts can create a telnet connection to the other one

Oh yeah ! That makes sense. Thanks a lot man. Since my exam got postponed coz of server problems I have few more days to prepare ., that means a few more doubts :D


Here's my next doubt. The question is in the attachment. It's a question that is in both testinside and pass4sure.

A network is shown and the question says:

"The RIP network shown has been fully operational for two days. Each routing table is complete. Which networks will be included in the next routing update from Apples router to Pears router ?"

The given answer is "A, B , C" but I think it's "A,B,C,D, E, F" since RIP broadcasts the entire routing table. May be Split Horizon may be used (which is not mentioned) but even then one of RIP's features is to send it's whole routing table, which after 2 days would include all networks right ???

[komalthecoolk]

Here's another doubt:

For a single OSPF area with two subnetworks in it., if there are few routers in one subnet and few in another subnet., while electing DR and BDR, are the DR and BDR elected for the whole area or for each subnet ??? This is a doubt from Testking 640-801 V114 Question 28 in Section 3: Compare and contrast key characteristics of LAN environments of Topic 4: TECHNOLOGY

[f.d]

As far as i knw, a DR is an interface of a router and belongs to a single network segment. The router’s other interfaces may be a BDR or DRother.
Correct me if m wrong

:)

[komalthecoolk]

DR is the designated router.., not an interface. I know that there is one DR and one BDR per OSPF area.., but in a testking question., they chose two DRs for each subnet that is withing a single area. That is where I'm confused.

[Visio]

I know that there is one DR and one BDR per OSPF area.., but in a testking question., they chose two DRs for each subnet that is withing a single area. That is where I'm confused.

There are 4 types of networks from an OSPF perspective:
1. Broadcast
2. Non-Broadcast Multi-Access (NBMA) (i.e. Frame-Relay or ATM)
3. Point-to-Point
4. Point-to-Multipoint

DR and BDR concepts holds for broadcast/NBMA networks and are not area specific. DR/BDR election is independent of the area of the network.
Remember that here is 1 DR per broadcast net. All routers attached to that
net accept & let the DR proxy for them.

[komalthecoolk]

@ Vijay: Oh yeah ! That's brilliant ! Man.., do you have some kind of hands on experience or have better books than I do ? Coz honestly none of these preparation books for CCNA have the complete stuff. Nor are they clear.

Btw.., can you or anyone help me out with my previous question too ?

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[komalthecoolk]

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The image shown is a layer 4 header ( i think) sent to a destination with the desination and source ports, mac addresses and ip addresses shown. The question asked is what will be the destination and source mac addresses and ip addresses and source addresses when the reply is sent to the original frame.

As far as I know., the source and destination addresses and port numbers interchange for the reply. But Testking says that the port numbers don't interchange because it's telnet !! That's the first time I'm hearing that.

Can someone help ???