Home > Ticket 13 – DHCP Helper-address

Ticket 13 – DHCP Helper-address

April 24th, 2018 in TSHOOT v2 Go to comments

Configuration on DSW1:

!
interface Vlan 10
 ip address 10.2.1.1 255.255.255.0
 ip helper-address 10.2.21.129
!

Note:
+ In this ticket you will find port-security configured on ASW1 but it is not the problem as the port-security is good (check with the “show interface fa1/0/1” command on ASW1 and you will see it is still in up/up state. Also if we use “ipconfig” command on Client1, we will see APIPA address (169.254.x.x).
+ 10.1.21.129 is the loopback1 interface of R4. The wrong IP address of 10.2.21.129 does not exist.

Ans1) DSW1
Ans2) IP DHCP Server (or DHCP)
Ans3) on DSW1 delete “ip helper-address 10.2.21.129” and apply “ip helper-address 10.1.21.129” command

Comments (30) Comments
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  1. Mick
    November 20th, 2014

    Yop Lukas, That’s right – You’ve to be a little patient in getting a valid IP DHCP address on the Packet Tracer Client, after fixing the problem in this Ticket # 13
    However, here’s a Little Tip for you:
    After fixing the problem, you can do a “wr” and then a “reload” on R4, or you can do a R4:

    #copy run start
    #copy start run

    (This method – (it works most often) – is a little faster, than the first one mentioned) :)

    Have fun :)

  2. Mick
    November 20th, 2014

    Lukas: Pls also study Posts by Oct 2 and Oct 4 regarding the issue!

  3. Mick
    November 20th, 2014

    Lukas: Pls also study Posts by Oct 2 and Oct 4 (right ABOVE) regarding the issue!

  4. Lukas
    November 20th, 2014

    Thank you Mick

  5. anita
    December 3rd, 2014

    hi guys can one click on the router for example R2 and do a show running-config to find out the problem

  6. Mick
    December 3rd, 2014

    Yes, Miss Anita – can one click on a router (preferably R4 in this case / ticket) and then do a show running-config to find out the problem :)
    Enjoy!

  7. Mick
    December 3rd, 2014

    Yes, Miss Anita – One can click on a router (preferably R4 in this case / ticket) and then do a show running-config to find out the problem :)
    Enjoy!

  8. Mluvly
    December 17th, 2014

    Hey guys, can someone please explain how the TSHOOT exam is cause i am confused from the demo i saw. Are all the tickets pointing to the same question or different questions with different tickets!! CONFUSED!!

  9. Mluvly
    December 17th, 2014

    Or better still post a link that can explain the exam better. Thanks.

  10. Jimmy
    December 17th, 2014

    Mluvly:
    The Link u need and ask for is right en front of your nose!!! => Info on Network Tut is the answer to all your problems and confusion!
    So please carefully study all the info here @ the Net Tut Pages, and think it over what you’ve just learned – Then do some TSHOOT Labs also, and you’ll be good to go! – But please HURRY UP since you’ve only got limited time until deadline by end of January 2015!!!
    Good Luck!

  11. anita
    January 13th, 2015

    thanks mick

  12. Ardak
    January 18th, 2015

    if it doesn’t work, you need to clear mac table

  13. Buddy
    January 18th, 2015

    Ardak:

    AFTER solving the TT#13 DHCP Problem on R4 – Just run this command sequenze on R4, to get the CHANGES properly loaded @ R4, so the Clients are getting their IP DHCP based Info more quickly and not least EFFICIENT:

    So, just run on R4:
    ena
    wr
    copy start run
    !
    Then go into the Config Tab on the Client PC and Switch back and forth between the Global/Settings button and the Interface/Fastethernet0 button there a few times – Then suddenly the Client gets his IPv4 address, and everything is fine!

    (In the rare case, “Copy start run” won’t Work ok on R4 – (Against all odds) – Pls do a R4 “wr” / “Reload” instead, to get the CHANGES properly loaded on R4!

  14. Neo
    January 23rd, 2015

    I followed the given steps and got DHCP address but could not able to ping web server after getting dhcp address from Client 1, what should be done??

  15. Buddy
    January 23rd, 2015

    @Neo:

    Pls study this procedure to verify that all is good after solving TT#13:

    First on R4:

    R4#sh ip dhcp bind
    IP address Client-ID/ Lease expiration Type
    Hardware address

    R4#conf t
    Enter configuration commands, one per line. End with CNTL/Z.
    R4(config)#no ip dhcp excluded-address 10.2.1.1 10.2.1.253
    R4(config)#ip dhcp excluded-address 10.2.1.1 10.2.1.2
    R4(config)#exit
    R4#
    %SYS-5-CONFIG_I: Configured from console by console

    R4#wr
    Building configuration…
    [OK]

    R4#copy start run
    Destination filename [running-config]?

    2573 bytes copied in 0.416 secs (6185 bytes/sec)
    R4#Reload or use “clear ip ospf process” command, for this to take effect

    %SYS-5-CONFIG_I: Configured from console by console

    R4#sh ip dhcp bind
    IP address Client-ID/ Lease expiration Type
    Hardware address
    10.2.1.4 0060.4744.A334 — Automatic ——!!!
    R4#

    Now moving to Client 1 PC for testing IPv4 Connectivity towards the external WEB Server like this:

    Packet Tracer PC Command Line 1.0
    PC>ipconfig

    FastEthernet0 Connection:(default port)

    Link-local IPv6 Address………: ::
    IP Address………………….: 10.2.1.4
    Subnet Mask…………………: 255.255.255.0
    Default Gateway……………..: 10.2.1.254

    PC>ping 209.65.200.241

    Pinging 209.65.200.241 with 32 bytes of data:

    Reply from 209.65.200.241: bytes=32 time=40ms TTL=122
    Request timed out.
    Reply from 209.65.200.241: bytes=32 time=84ms TTL=122
    Reply from 209.65.200.241: bytes=32 time=36ms TTL=122

    Ping statistics for 209.65.200.241:
    Packets: Sent = 4, Received = 3, Lost = 1 (25% loss),
    Approximate round trip times in milli-seconds:
    Minimum = 36ms, Maximum = 84ms, Average = 53ms

    PC>
    Now TT#13 Works 100% OK!

    Now try the procedure once more YOURSELF to make it Work – OK!?

  16. Neo
    January 24th, 2015

    And how to differentiate questions for client having 169.x.x.x IP address during the exam? We will be having 4 questions in which client has 169 Ip address.

  17. Anonymous
    January 26th, 2015

    Do i need to configure every ticket in exam!? or just check the problem? please help me im taking the exam on thursday.. thanks

  18. Mick
    January 26th, 2015

    Just Check the tickets and identify the problem…Check the demo link below to get a feel of the exam
    https://www.cisco.com/web/learning/le3/le2/le37/le10/tshoot_demo.html

  19. Cisconet
    January 27th, 2015

    @Anonymous you will just identify the problem and pick the right answer from the given answers…i hope that helps..and best of luck for your exam!

  20. CiscoAnon
    January 28th, 2015

    Just a question for my own knowledge purposes – why do they still want to apply the “ip dhcp excluded-address 10.2.1.1 10.2.1.2” at the end? Wouldn’t this exclude both those IPs from DHCP?

    I thought that the clients were supposed to get 10.2.1.1 and 10.2.1.2.

  21. Buddy
    January 28th, 2015

    @CiscoAnon:

    Yes, one could that thought – however, if you take a look at the official Cisco 642-832 TSHOOT L2/L3 Topology Diagram:

    https://www.networktut.com/tshoot-share-your-experience

    You’ll notice that indeed IP: 10.2.1.1 has been choosen as the VLAN 10 SVI on DSW1, while IP: 10.2.1.2 has been choosen as the VLAN 10 SVI on DSW2 within the TSHOOT.com Topology.

    Therefore we need to “reserve” indeed theese two IP’s for this purpose from the “Dynamic” DHCP Pool on DHCP Server R4, to avoid any IP addressing conflicts within the TSHOOT Topology…

    Hope this clarify the issue within Ticket # 13!?

    Thank you!

  22. CiscoAnon
    January 28th, 2015

    Thanks @Buddy! Very helpful!

  23. CiscoKid
    March 18th, 2015

    Shouldn’t the exclude statement ALSO include the hsrp ip?
    10.2.1.254

  24. Cath
    March 23rd, 2015

    No, hsrp ip 10.2.1.254 is already excluded on a separate command line within DHCP Server R4.

  25. Route Professor
    April 18th, 2015

    Can somebody explain why the ip helper-address, on the DSW1, has been set to the IP address of the loopback 21 interface of R4 and not to the actual IP address of the DHCP server (10.1.4.5)? Also, I cannot understand how this works… I am trying to find a configuration example from Cisco site or anywhere else without any luck…

  26. Sam
    April 19th, 2015

    Fessor:

    The IP helper address of: 10.1.21.129/27 which is configured within vlan 10 on DSW1, belongs to a dedicated Loopback (21) interface on DHCP Server R4, has been set to indeed THIS address on R4, and not to the mentioned address of 10.1.4.5 on the DHCP server, simply because Cisco LIKES IT that way, and don’t think it should be all to easy for the proff level Network Candidate @ exam!

    Thus the referrenced IP helper address at DSW1 does NOT necessarily have to be the fa0/0 (ingress) 10.1.4.5 interface on the DHCP Server (R4) – in fact, it can be ANY working “up/up” Interface on R4, as long DSW1 is having a VALID and working IP route towards the mentioned “IP helper target” on R4.

    Hope this helps!?

  27. Route Professor
    April 25th, 2015

    @ Sam:

    Thanks for the explanation! I have not found a configuration example like this, nor an “official” explanation of this configuration, though! Not in the study guides, nor in the Cisco site…
    So, this is really not kind of them…But like you said, they like to do that…
    That is why every time I go for a Cisco exam, I promise to myself that this will be my last Cisco exam…and every time, I do not keep this promise! ;)

  28. Sam
    April 26th, 2015

    Fessor:

    Yes, definitely agree w. you in the fact, that setting the ip-helper address to the one at the ingress I/F IP address on the DHCP Server will be the normal “best practice” within most IP Networks.

    Thus the good thing about this alternative TSHOOT DHCP Config demonstrated here on Net-Tut, is that you – in addition – learn about also this quite rare config possibility within the Cisco IOS, not satisfactory explained elsewhere.

    So, one can say, that “Network Tut” is here a very good and efficient weapon, in the fight to defeat the (quite often) BUGGY Cisco “exam monster”, and perhaps the reason for you do not always keep your Cisco exam promises mentioned above ;)

    Anyway Good Luck @ exam :)

  29. Route Professor
    April 26th, 2015

    @ Sam:
    I am quite impressed that I did not find such a configuration example by Cisco. Probably, I did not search that much…but anyway… Now, at least, I know an alternate configuration for DHCP relay!
    Going tomorrow for the exam to become CCNP after 13 months of studying… :-)
    Then onto Design….Damn…I did not kept my promise again… :-p
    Thanks!

  30. IP-Helper
    May 4th, 2015

    @Sam

    I have to disagree with the statement that setting an ingress interface as DHCP server is “best practice” especially when you have a redundant topology like this.

    lets say that you use 10.1.4.5 as ip-helper in both DSW1 and DSW2, what will happen when that interface goes down in R4? Clients will not get an IP adress since DSW1 or DSW2 cant reach the DHCP server.

    Lets say you use an IP address on a logical interface(loopback interface) instead as IP-helper and this IP address is then advertised via EIGRP to DSW1 and DSW2. What will happen now if interface with IP 10.1.4.5 goes down? Clients will still get an IP address since they can reach the DHCP server via DSW2.

    This is why it is always better to use a logical interface in a redundant topoplogy. You dont have to depend that a physical interface is up since you have several ways to reach the destination.

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