TCP UDP Questions 2
Question 1
Explanation
Unlike TCP which uses the sequence numbers to rearrange the segments when they arrive out of order, UDP just passes the received datagrams to the next OSI layer (the Session Layer) in the order in which they arrived.
Question 2
Question 3
Explanation
In Asymmetric routing, a packet traverses from a source to a destination in one path and takes a different path when it returns to the source. This is commonly seen in Layer-3 routed networks.
Issues to Consider with Asymmetric Routing
Asymmetric routing is not a problem by itself, but will cause problems when Network Address Translation (NAT) or firewalls are used in the routed path. For example, in firewalls, state information is built when the packets flow from a higher security domain to a lower security domain. The firewall will be an exit point from one security domain to the other. If the return path passes through another firewall, the packet will not be allowed to traverse the firewall from the lower to higher security domain because the firewall in the return path will not have any state information. The state information exists in the first firewall.
Reference: http://www.cisco.com/web/services/news/ts_newsletter/tech/chalktalk/archives/200903.html
Specifically for TCP-based connections, disabling stateful TCP checks can help mitigate asymmetric routing. When TCP state checks are disabled, the ASA can allow packets in a TCP connection even if the ASA didn’t see the entire TCP 3-way handshake. This feature is called TCP State Bypass.
Reference: https://supportforums.cisco.com/document/55536/asa-asymmetric-routing-troubleshooting-and-mitigation
Note: The active/active firewall topology uses two firewalls that are both actively providing firewall services.
Question 4
Explanation
A device that sends UDP packets assumes that they reach the destination. There is no mechanism to alert senders that the packet has arrived -> Answer A is not correct.
UDP throughput is not impacted by latency because the sender does not have to wait for the ACK to be sent back -> Answer B is not correct.
UDP does not negotiate how the connection will work, UDP just transmits and hopes for the best -> D is not correct.
Therefore only answer C is left.
Question 5
Explanation
The command “show tcp brief numeric” displays a concise description of TCP connection endpoints.
Question 6
Question 7
Explanation
TCP starvation/UDP dominance likely occurs if TCP-based applications is assigned to the same service-provider class as UDP-based applications and the class experiences sustained congestion.
TFTP (run on UDP port 69) and SNMP (runs on UDP port 161/162) are two protocols which run on UDP so they can cause TCP starvation.
Note: SMTP runs on TCP port 25; HTTPS runs on TCP port 443; FTP runs on TCP port 20/21
Don’t agree with Q4. I think the correct is C
Sorry, I think the correct is B)
Question 4
I agree with you, B is the correct one to me, C does not make any sense for UDP
Question 4. Correct answer is C.
http://smutz.us/techtips/NetworkLatency.html
Question 5, i tried the BGP practical following was the observation:-
1) Using command ” Show tcp brief” :- i can see the same output as seen in the command “Show tcp brief numeric” also both shows the state field as “ESTAB”
2) Using command ” Show tcp brief All” :- i can see both state field i. e. “ESTAB” as well as “LISTEN”
In question its stating both field “ESTAB & LISTEN” so answer will be ” Show Tcp Brief All ”
Please some one clarify or correct me
I agree the answer C is most better in Q4, but I have a misunderstanding with it. The term ‘latency’ have a meaning between TWO events. But from the point of view of receiver there is only ONE event – recieving the packets. The receiver just gets these packets immediately by each other. The receiver doesn’t aware about the sending time. So, why it should hold the data in the buffer? It should just pass the received datagrams to the next OSI layer, as explained above in Q1. Isn’t it?
I agree with @salman about Q5. The most better answer is B (show tcp brief all).
Hi All,
Q5.. What show command is used here?
TCB Local Address Foreign Address (state)
6523A4FC 10.1.25.3.11000 10.1.25.3.23 ESTAB
65239A84 10.1.25.3.23 10.1.25.3.11000 ESTAB
653FCBBC *.1723 *.* LISTEN
A. show tcp brief
B. show tcp brief all
C. show tcp brief numeric
D. show tcp brief ip
I’ve used real equipment and many simulators and the commands
sh tcp brief ip & sh tcp brief numeric don’t show up as an option.
I’ve also checked the | section part also with nothing.
@Digitaltut Can you please update this question if incorrect?
Hi,
The answer correct Q5 is C.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-s3.html#wp4294670608
It turns out, Q5 is a tricky question. The documentation says “Without this keyword [all], endpoints in the LISTEN state are NOT shown.” But we can see the LISTEN state in the output of “show tcp brief numeric” command (without “all”) below. May be because there is no endpoints. Anyway, this question was made to confuse us, but now I think C is correct. Thanks to Rukia24.
Back to Question 4. If C is the and answer then the answer for Question 6 is both B and C since 4 C is a result of latency then in 6 If the answer is C then the answer is also B based on the answer in 4.
So perhaps the answer in 4 really is B
It looks like the all is the only option that shows the listeners
r1#sh tcp brief ?
all All end-points (even listeners)
numeric Numeric Display
| Output modifiers
r1#sh tcp brief numeric
TCB Local Address Foreign Address (state)
7F660477F5C8 10.118.129.98.42716 10.118.129.102.179 ESTAB
7F65EF949D40 68.136.175.154.26243 68.136.175.153.179 ESTAB
7F6606B590E0 10.118.129.109.22 146.170.64.73.60611 ESTAB
7F6606938F60 10.118.129.98.179 10.118.129.101.42540 ESTAB
r1#sh tcp brief ?
all All end-points (even listeners)
numeric Numeric Display
| Output modifiers
r1#sh tcp brief all
TCB Local Address Foreign Address (state)
7F660477F5C8 10.118.129.98.42716 10.118.129.102.179 ESTAB
7F65EF949D40 68.136.175.154.26243 68.136.175.153.179 ESTAB
7F6606B590E0 10.118.129.109.22 146.170.64.73.60611 ESTAB
7F6606938F60 10.118.129.98.179 10.118.129.101.42540 ESTAB
7F6605D7EB18 0.0.0.0.179 68.136.175.153.* LISTEN
7F6605D7E198 0.0.0.0.179 10.118.129.102.* LISTEN
7F6605D6FD00 0.0.0.0.179 10.118.129.101.* LISTEN
r1#
I tried serval router in real sitsuations(c881/c2911)
” show tcp all bri “would be only one answer that show “Listen”~
I also saw example in cisco web,”https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-s3.html#wp4294670608” , it shows the answer is C.
But I think it is wrong printed in web browser.
We should choose the right answer without getting right scores.
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I think that Q5 should be B not C
show tcp brief numeric will not show listening ports
show tcp brief all will show listening ports.
Therefor the answer must be B
Proof:
R1#sh tcp brief numeric
TCB Local Address Foreign Address (state)
0F1ECBF8 155.1.13.1.38949 155.1.13.3.179 ESTAB
0F22C2D8 155.1.146.1.11084 155.1.146.6.179 ESTAB
0F1CEEC0 155.1.146.1.49274 155.1.146.4.179 ESTAB
R1#
R1#
R1#sh tcp brief all
TCB Local Address Foreign Address (state)
0F1ECBF8 155.1.13.1.38949 155.1.13.3.179 ESTAB
0F22C2D8 155.1.146.1.11084 155.1.146.6.179 ESTAB
0F1CEEC0 155.1.146.1.49274 155.1.146.4.179 ESTAB
0F0488D0 0.0.0.0.179 155.1.13.3.* LISTEN
0F047A58 0.0.0.0.179 155.1.146.6.* LISTEN
0F040FE0 0.0.0.0.179 155.1.146.4.* LISTEN
I agree, Q5 seems to be wrong.
all
(Optional) Displays status for all endpoints in Domain Name System (DNS) hostname format. Without this keyword, endpoints in the LISTEN state are not shown.
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-s3.html
I wonder how many of wrong answers are on this site.
numeric – Displays status for !! all !! endpoints in !! IP format !!.
Numeric is the correct answer
Real and effective, can be used as a reference, very effective, I hope to help you.
W w
w.cc iedumps.xyz/ccie_rs.php?ut m_source=bbs&utm_medium=bbs
Q5 right answer is C (show tcp brief numeric).
Just read here: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-s3.html#wp4294670608
this part:
show tcp brief [ all | numeric ]
all – (Optional) Displays status for all endpoints in Domain Name System (DNS) hostname format. Without this keyword, endpoints in the LISTEN state are not shown.
numeric – (Optional) Displays status for all endpoints in IP format.
Ou, sorry, about Q5, right is B of course.
Q5 Right Answer is B
R1#show tcp brief ?
all All end-points (even listeners)
R1#show tcp brief all
TCB Local Address Foreign Address (state)
11ABF408 1.1.1.1.23 1.1.1.4.60196 ESTAB
0E7EDD78 1.1.1.1.44932 1.1.1.4.179 ESTAB
0E7E4E50 1.1.1.10.48382 1.1.1.11.179 ESTAB
11D70A08 0.0.0.0.179 1.1.1.11.* LISTEN
0D7731D8 0.0.0.0.179 1.1.1.4.* LISTEN
Q4 and Q6 have the same theory behind. UDP is immune to latency. Receiver will have to buffer more data, before sending packets to higher layers (VoIP soft phone for example)
So Q4 answer is C and Q6 Answer is B(Digitaltut please put correct answer,based on your presented theory on that page)
@Dany1, see the link:
https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/command/iap-cr-book/iap-s3.html#wp4294670608
right answer is “show tcp brief numeric”.
If you check this link you will see exactly the examle from question (even IP-addres are the same as in question).
Q5 = C 100%
This is from cisco website..
Router# show tcp brief numeric
TCB Local Address Foreign Address (state)
6523A4FC 10.1.25.3.11000 10.1.25.3.23 ESTAB
65239A84 10.1.25.3.23 10.1.25.3.11000 ESTAB
653FCBBC *.1723 *.* LISTEN
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Which two causes of latency are true? What is the correct answer?
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Q5
B is correct… this is output from a device:
R7#show tcp brief numeric
TCB Local Address Foreign Address (state)
11987AB0 7.7.7.7.179 4.4.4.4.43298 ESTAB
11B19BF0 2001:DB8:ACAD:7::7.28333 2001:DB8:ACAD:4::4.179 ESTAB
0F99E5E8 2001:DB8:ACAD:7::7.25902 2001:DB8:ACAD:6::6.179 ESTAB
11A68428 7.7.7.7.30154 6.6.6.6.179 ESTAB
R7#show tcp brief all
TCB Local Address Foreign Address (state)
11987AB0 7.7.7.7.179 4.4.4.4.43298 ESTAB
11B19BF0 2001:DB8:ACAD:7::7.28333 2001:DB8:ACAD:4::4.179 ESTAB
0F99E5E8 2001:DB8:ACAD:7::7.25902 2001:DB8:ACAD:6::6.179 ESTAB
11A68428 7.7.7.7.30154 6.6.6.6.179 ESTAB
11924CF0 ::.179 2001:DB8:ACAD:6::6.* LISTEN
11923260 ::.179 2001:DB8:ACAD:4::4.* LISTEN
11922120 0.0.0.0.179 6.6.6.6.* LISTEN
1191B900 0.0.0.0.179 4.4.4.4.* LISTEN
Still do you need to be convinced?
It is unfortunate that I am paying for this service when there are many wrong answers being given out.
show tcp brief all — gives the listeners as well as ESTABLISHED
show tcp brief numeric only gives ESTABLISHED