CCNA Access List Sim
Question
An administrator is trying to ping and telnet from Switch to Router with the results shown below:
Switch>
Switch> ping 10.4.4.3
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.4.4.3,timeout is 2 seconds:
.U.U.U
Success rate is 0 percent (0/5)
Switch>
Switch> telnet 10.4.4.3
Trying 10.4.4.3 …
% Destination unreachable; gateway or host down
Switch>
Click the console connected to Router and issue the appropriate commands to answer the questions.
Answer and Explanation
Note: If you are not sure about Access-list, please read my Access-list tutorial. You can also download this sim to practice (open with Packet Tracer) here: http://www.9tut.com/download/9tut.com_CCNA_Access_List_Sim.pkt
For this question we only need to use the show running-config command to answer all the questions below
Router>enable
Router#show running-config
Question 1:
Which will fix the issue and allow ONLY ping to work while keeping telnet disabled?
A – Correctly assign an IP address to interface fa0/1
B – Change the ip access-group command on fa0/0 from “in” to “out”
C – Remove access-group 106 in from interface fa0/0 and add access-group 115 in.
D – Remove access-group 102 out from interface s0/0/0 and add access-group 114 in
E – Remove access-group 106 in from interface fa0/0 and add access-group 104 in
Answer: E
Explanation:
Let’s have a look at the access list 104:
The question does not ask about ftp traffic so we don’t care about the two first lines. The 3rd line denies all telnet traffic and the 4th line allows icmp traffic to be sent (ping). Remember that the access list 104 is applied on the inbound direction so the 5th line “access-list 104 deny icmp any any echo-reply” will not affect our icmp traffic because the “echo-reply” message will be sent over the outbound direction.
Question 2:
What would be the effect of issuing the command ip access-group 114 in to the fa0/0 interface?
A – Attempts to telnet to the router would fail
B – It would allow all traffic from the 10.4.4.0 network
C – IP traffic would be passed through the interface but TCP and UDP traffic would not
D – Routing protocol updates for the 10.4.4.0 network would not be accepted from the fa0/0 interface
Answer: B
Explanation:
From the output of access-list 114: access-list 114 permit ip 10.4.4.0 0.0.0.255 any we can easily understand that this access list allows all traffic (ip) from 10.4.4.0/24 network
Question 3:
What would be the effect of issuing the command access-group 115 in on the s0/0/1 interface?
A – No host could connect to Router through s0/0/1
B – Telnet and ping would work but routing updates would fail.
C – FTP, FTP-DATA, echo, and www would work but telnet would fail
D – Only traffic from the 10.4.4.0 network would pass through the interface
Answer: A
Explanation:
First let’s see what was configured on interface S0/0/1:
Recall that each interface only accepts one access-list, so when using the command “ip access-group 115 in” on the s0/0/1 interface it will overwrite the initial access-list 102. Therefore any telnet connection will be accepted (so we can eliminate answer C).
B is not correct because if telnet and ping can work then routing updates can, too.
D is not correct because access-list 115 does not mention about 10.4.4.0 network. So the most reasonable answer is A.
But here raise a question…
The wildcard mask of access-list 115, which is 255.255.255.0, means that only host with ip addresses in the form of x.x.x.0 will be accepted. But we all know that x.x.x.0 is likely to be a network address so the answer A: “no host could connect to Router through s0/0/1” seems right…
But what will happen if we don’t use a subnet mask of 255.255.255.0? For example we can use an ip address of 10.45.45.0 255.255.0.0, such a host with that ip address exists and we can connect to the router through that host. Now answer A seems incorrect!
Please comment if you have any idea for this sim!
Other lab-sims on this site:
zim zim zim zim
what do you mean
{eigrp with an extra unneccessary network to be removed}
what do we do?
@atr – The answer is A. You can check Cisco’s page on DHCP. It clearly says that.
http://www.cisco.com/en/US/docs/ios/12_0t/12_0t1/feature/guide/Easyip2.html
Go to the end of the page. In the Glossary look for “address conflict”. It’ll give you the answer.
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No configuration present in the router. :(
It’s questions like this one that make the whole “Cisco no-red-herring questions” ethos a complete fabrication of the truth.
Something similar came up in my last exam, They say things like “Allow ONLY icmp traffic while keeping telnet disabled”.. to me that means:
permit icmp any any
deny ip any any
and cannot mean anything else.
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question 1 says you need to enable telnet and icmp, however the answer denies telnet traffic. can anyone explain?
@Squeeb.
If you need to alow ICMP and deny telnet the statment in acs should be:
access-list 100 permit ICMP any any
access-list 100 deny TCP any any eq telnet
there is an inplicit line at the end of every ACL that denyes all traffic.
That said, I think that’s the solution…
hi,i greet you all,am really impressed with all your comments and qustions,none is wasteful,i will be writing my icnd1 exam by this month ending,but am still having a problem with sim,n configuraton, and little bits of subnetting,am kind of confused ,pls i need your advice,and your surport,bsogbaike@yahoo.com. thanks
after all configuration I got ping 10.4.4.3 but I am not ping telnet 10.4.4.3.say why this happene. How to ping telnet command
@raj u cannot ping telnet it is application uses port 23 used for making connection to router or switch
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I’m find’ subnett’ a bit tough.how can u assist?
Q3 answer A IS CORRECT. Reasons:
Interface s0/0/1 has an ipaddress 10.45.45.1/255.255.255.0 ===> Implying that it is connected to a network whose address uses a mask of 24. So it is reasonable to assume that the network mask to be 24 or greater for networks connected to s0/0/1.
Q1
i think access-list 106 can answer correctly this question. i don’t understand why access list 104 has been chosen instead acl 106.
plz can anyone explain me why does”access-list 106 permit icmp any any echo-reply” not permit ping to work properly?
@softwil
ACL 106 permit for ‘echor reply’ on inbound direction of f0/0 interface (in this case it doesnt matter because, we ping from switch to router sa echo request goes sw->rou, and ‘echo reply’ goes rou->sw) but implict deny at the end of ACL (deny all) block the ‘echo reguest’, thats why ping is not working.
thks bgrpl!
it s easy..but, it will collaps of our mind….much more acl
Thank you 9tut, this site filled the knowledge gaps I had in my preparation for the CCNA exam and was key in helping me to pass my exam. I appreciate everything, you all are wonderful.
Best Regards
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God Bless.
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Good Afternoon All,
@ Rosi. I have to retake the exam due to techical issues at the testing site, but I can confirm that there ARE drag and drop questions ( at least I had some). I got questions 1 from section 3 and 1/5 of section 4 on 9tut.
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show ip dhcp conflict
To display address conflicts found by a Cisco IOS Dynamic Host Configuration Protocol (DHCP) Server when addresses are offered to the client, use the show ip dhcp conflict EXEC command.
show ip dhcp conflict [address]
Syntax Description
address
(Optional) Specifies the IP address of the conflict found.
Defaults
None
Command Modes
EXEC
Usage Guidelines
This command first appeared in Cisco IOS Release 12.0(1)T.
The server detects conflicts using ping. The client detects conflicts using gratuitous Address Resolution Protocol (ARP). If an address conflict is detected, the address is removed from the pool and the address will not be assigned until an administrator resolves the conflict.
Please send latest dump to wiredup@nf.sympatico.ca,,Thanks
Whenever there is a address conflict in the DHCP server the address is usually removed from the pool for the a specific time period configured by an administrator
I fee so dumb, please somebody help!
Q 1: The explanation says: “Remember that the access list 104 is applied on the inbound direction so the 5th line “access-list 104 deny icmp any any echo-reply” will not affect our icmp traffic because the “echo-reply” message will be sent over the outbound direction.”. So if I understand correctly, we call icmp echo-reply the answer that we get when we ping some address. And in this case it can come to the router on the outbound (free) side of the port. But it seems to me it needs to be reverse: the echo-reply (the ping answer) should be able to come on the INbound side and be blocked by the outbound. Ohhhh, please help? Im lost. Every side can be IN and every can be OUT depending from where you look. Why can not they explain this easier?
Q 1: 104 inbound means: we can ping to someone but can not get their echo-reply (answer) does not it? So by applying 104 in we can not actually ping and expect to get an answer. It will be blocked by the IN port. So how can we say then that the answer is satisfied (meaning that we can ping) but actually we should not be able to receive an answer of the ping- meaning we can not ping???
Any smarties out there?
@bgrpl, thanks dude for your response to softwill. I was too messed with question 1, now it’s clear with your answer.
address conflict—A duplication of use of the same IP address by two hosts. During address assignment, DHCP checks for conflicts using ping and gratuitous ARP. If a conflict is detected, the address is removed from the pool. The address will not be assigned until the administrator resolves the conflict.
Question 3…. One of CCNA nonsense never-hapens-in-your-life questions ..
OSPF and EIGRP routing will fail as multicast updates (224.0.0.X) will be blocked. We see no static routing configuration in “sh run” output, so that means the only route associated with s 0/0/0 interface in the router table is:
10.45.45.0/24 direcly connected to s 0/0/0
Any hosts from this network would be blocked by the access list. So the only correct answer seems to be A.
ok … The connection through s0/0/0/1 could actually work if the packets from source like X.X.X.0 would take another return-path to the sender. I mean:
Packets from source: X.X.X.0 with subnet mask from /23 to /8
Incoming interface: s0/0/1
Return interface: NOT s0/0/1
The connection like that could work.
P.S. I have made a mistake in the interface number in my previous post. Should be s0/0/1
I think answer C is correct because there is no such form of command “access-group 115 in”
In interface configuration mode you must type “ip access-group 115 in”. By typing “access-group 115 in” without word “ip” IOS just reject your input, thus access list 102 will remain applied.
Nuts&Bolts: Are you CCIE?
pls send to me the ccna dumps.thanks in advance.
Question 1:
Which will fix the issue and allow ONLY ping to work while keeping telnet disabled?
A – Correctly assign an IP address to interface fa0/1
B – Change the ip access-group command on fa0/0 from “in” to “out” <–seems to be correct
m.
The easiest way to answer to Q3 is that there is an implicit deny at the end of the access list which we cannot see. Hence, all the traffic will be automatically blocked. I don’t know why people are writing gigantic answers just to answer Q3.
regarding Q1
B-Change the ip access-group command on fa0/0 from “in” to “out
not correct becuase this will allow telnet and ping as well.
I downloaded the pkt, regarding the Q3 it did not overide as i execute the command the s0/0/0 has now 2 ACL: ip access-group 115 in and ip access-group 102 out in the explanation it says override so in my unerstanding the first ACL will be read and the second ACL will just be ignored?
I downloaded the pkt, regarding the Q3 it did not overide as i execute the command the s0/0/0 has now 2 ACL: ip access-group 115 in and ip access-group 102 out in the explanation it says override so in my unerstanding the first ACL will be read and the second ACL will just be ignored?
Does anyone out there have Packet Tracer 6 or later? Please send to aaegh7@gmail.com. My version (V5) does not support iBGP…I’m preparing for CCIE.
Thanks in advance.
@Enthusiast
Check your directions. You can only have 1 access list per interface, per protocol, per direction. You have two ACLs on your interface because one is facing in and the other is facing out. The original question has ACL 102 IN. If you apply ACL 115 IN it will over write ACL 102
is this lab subject to any changes during the exam? thank you very much.