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 (27) Comments
Comment pages
1 5 6 7 211
  1. how to dhcp
    April 26th, 2019

    Verify:
    ipconfig on Client 1 & 2
    ping 209.65.200.241

    on ASW1:
    show interfaces status – check if you have any down or in err-disabled statue
    show acces-list – this is routine just to check if something is blocking vlan 10 traffic and the ip subnets related to R4
    show vlan – verify that vlan 10 exists and ports are assigned

    on DSW1:
    show ip int brief – verify SVI 10 is up and has IP address
    show vlan – verify that VLAN 10 exists, otherwsie SVI won’t route for it
    show run int vlan 10 – check config on SVI
    ping 10.2.21.129 – try to ping current helper-address, if you can’t you have to check if it is the correct IP

    Remember that per topology Client 1 needs to obtain IP from 10.2.1.0/24 range and Client 2 from 10.2.2.0/24 range.
    We also have an arrow on the topology pointing to R4 for DHCP service.
    The idea of helper-address is to relay the DHCP packets to network device that is able to process discover/offer/request/ack packets
    So whatever IP you have in “ip helper-address” it needs to be reachable , i.e IP connectivity, we know that DSW1 has a default route via EIGRP towards R4
    – therefore the only requirement left is R4 to have active interface with an IP address of whatever is in the “ip helper-address” command
    – Our sim is configured in a way that DSW1 cannot ping 10.2.21.129 because that IP doesn’t exist on the network

    on R4:
    show run
    In our sim we see “network 10.2.1.0 255.255.255.0” and is the pool where Client 1 only will obtain his IP from
    We also have:
    ip dhcp excluded-address 10.2.1.1 10.2.1.2
    ip dhcp excluded-address 10.2.1.254
    – this is just a list of IP addresses that should not be assigned, this is not a range
    – these are the IP addresses of the SVIs for VLAN 10 on DSW1/2
    – you also have the exclude 10.2.1.254 which is the HSRP virutal IP on DSW1/2

    show ip int brief – check if there are any interfaces with 10.2.21.129, there aren’t
    – remember the default route in EIGRP is redistributed from OSPF, so ideally you are looking for a network that is reachable via OSPF on
    – this can aslo work with “ip helper-address 10.1.4.5”

    show ip ospf database – you can see LSA Type 1 for 10.1.21.129
    show ip int brief -> Loopback 1 has IP of 10.1.21.129

    on DSW1
    ping 10.1.21.129 -> success
    conf t
    int vlan 10
    no ip helper-address 10.2.21.129
    ip helper-address 10.1.21.129

    The configuration will work even if you point the helper-address to any of the other interface IPs of R4, as long as they are reachable.
    The only requirement is that R4 is able to process DHCP packets and is one-hop away from DSW1.

  2. Forever More
    May 11th, 2019

    Took the exam yesterday
    (This site is spot on) – use it to study

    This question took me almost an hour and cost me the time required to answer all the rest of the questions (I answered 18 of 24) and thus failed

    Don’t let time derail you

  3. Johnny
    May 13th, 2019

    Passed on May 10th 2019 with 946/1000.
    24 questions on exam: 10 MCQs, 12 tickets, BGP and HSRP simlet.
    Thanks mm for detailed review and you guys here as well as Networktut team.
    Chinese dump is valid however MCQs answers in it are not totally correct.
    You should read all recent comments here to get your own correct answers.
    Good luck!

  4. Johnny
    May 13th, 2019

    Contact: ballking242(at)gmail(dot)com

  5. abdou
    May 18th, 2019

    hi
    please sent dump :{email not allowed}

  6. abd
    May 18th, 2019

    please sent dump :rouam10(at)yahoo(dot)fr

  7. Anonymous
    July 24th, 2019

    Hey guys, this answer confused me. I was confused moreso becuase I couldnt understand why the loopback was picked (there is nothing in the configs that point anything dhcp related to the loopback interface, which really confused me).

    so here goes:

    BEST PRACTICE states that your helper address should be the LOOPBACK address, because its a virtual interface, and never goes down.

    so you have the option to pick between loopback 1, or loopback 0.
    The only correct answer shows Loopback 1 being the preferred ip-helper address.

    i hope this helps clear up anything.

  8. PJ
    August 18th, 2019

    This ticket in Packettracer is broken. Networktut please can you take a look. IPhelper is correct, but still no IP addr on client1

  9. eLMo
    August 27th, 2019

    Could we check this issue by another way? If both clients have AIPA IPs and they are in the same vlan, we could ping each other (fix dhcp). If not, ports security was applied…

  10. DOTTMAN
    September 23rd, 2019

    Hi Guys. If you want to download freedump 300-135 go in my link. Last updated 08/08/2019

    htt ps : //w ww. youtu be. com/watch?v= yzG7EKVVz_0

  11. dumper boy
    September 23rd, 2019

    did you check the correct answers in the packet tracer you can see it at the bottom part left side. The issue was the DHCP excluded address covers the entire 10.2.1.0/24 subnet thus not leasing any ip address. This is not the same issue with ip helper ticket

  12. supa4sf1
    September 23rd, 2019

    This one got me off guard. Even though the configuration of the ip helper on DSW1 is incorrect, the configuration on DSW2 *is* correct. In this case, the client would still get an ip address as both of the DSWx SVI’s would receive the DHCP Discover – only DSW2 would get the directed unicast. I’ve tested this in the lab (using Cisco VIRL). Does anyone have any insight on this?

  13. Helper
    October 27th, 2019

    PJ,

    The problem in packet tracer is that all addresses are excluded from the DHCP pool with the following lines on R4:

    ip dhcp excluded-address 10.2.1.254
    ip dhcp excluded-address 10.2.1.1 10.2.1.253

    to fix do the following:

    no ip dhcp excluded-address 10.2.1.1 10.2.1.253
    ip dhcp excluded-address 10.2.1.1 10.2.1.3

    This is the problem in the packet tracer demo files that I downloaded from this site.

  14. Spaurito
    October 31st, 2019

    Helper…thanks for the catch. Just updated my local copy

  15. Sami
    November 18th, 2019

    @ DOTTMAN

    Go To Hell you ppl search a place to do all shit make ppl fool

    what a question ” if you people want free dumps ” ????

    don’t put garbage in this group

  16. NX
    November 21st, 2019

    @supa4sf1 – First of all tank you for this insight. So I’m not dreaming :P – I ended up at the very same spot. You are right in real world it will work as DSW2 with correct config will take care of it. I’m having 15+ years of experience and CCIE(expired) preparing for re-cert of all my CCxPs. And yes, I would kill a lot of time on this one if I didn’t saw it beforehand here. I’m so angry on Cisco for those dumb exams where you can fail due to stupid things like this. Meaning you wanna cisco cert? No matter how good you are you need to dump it or cheat it in some way to see their messed up questions beforehand to pass it.
    Even anyone whom pass TSHOOT will fail miserably in real life because essential L2 tshoot commands are just not there as show arp, show mac address-table, show etherchannel, show VLAN X, show int X trunk even sh int statu is in question… In real life on bigger or more complex switch show run is just not an option it’s too complex to analyze it in reasonable timeframe.
    … EOF (End OF Frustration) …
    supa4sf1 and networktut.com thanks again for all your help!

  17. taking exam soon
    December 1st, 2019

    what is question on below answer

    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

  18. Cisco Tshoot
    December 7th, 2019

    I failed the exam on Dec 3, 2019. This question comes .

    Packet Tracer in this website for this question is wrong.

    However, in the exam check if DSW1 helper address is 10.2.21.129

  19. subzero
    December 7th, 2019

    The answers for this question seem have changed.

    One answer said to delete the IP helper address 10.1.21.129 and configure it under FastEthernet1/0/1, another answer offered to configure it under a DHCP pool, an other again said to change the IP to 10.2.21.0 /24.

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    December 12th, 2019

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  21. Lets-go
    December 31st, 2019

    sub-zero
    you can configure ip helper on an interface that listens to broadcast of the pcs or on interface vlan. but you cant configure it on a dhcp pool.

  22. Anonymous
    January 2nd, 2020

    PJ

    In the Packettracer if the Client 1 does not get the DHCP address, just shut/no shut the Vlan10 interface on the DSW1.

  23. Anonymous
    January 2nd, 2020

    PJ

    If the shut/no shut of the Vlan10 interface on the DSW1 does not work, just reload the R4. It worked for me.

  24. grizo
    January 9th, 2020

    New Packet Tracer Lab 13 on this site:

    R4:

    ip dhcp excluded-address 10.2.1.1 10.2.1.253

    This was excluding the whole 10.2.1.0/24 network, PC1 won’t get an ip address.

    conf t
    no ip dhcp excluded-address 10.2.1.1 10.2.1.253
    end
    wr

    *** I had to reload R4 too, if not, DHCP never would provide an ip to PC1, everything ok after reloading it.

    The lab has other issues, as 10.1.1.8/30 network not declared in “router eigrp 10”

  25. ccnp-acquirer
    January 13th, 2020

    did not pass. I was confident that I answered all questions correctly since I am good at troubleshooting. Only sim that I could not find a correct answer for was: ipconfig on Client 1 showed 169.xx address. Obvioulsy not getting a DHCP address. When I looked at ASW1 (show run), the links to Client 1 and Client 2 were shutdown. Obviously if the link between host and Client are shutdown, the client will never get an IP address from the DHCP server. But I could not locate a Solution to the 3rd part of the question that also had “no shutdown” for Fa1/0/1. I do not like Cisco’s approach to testing since there is no recourse for an audit. Besides in the real-world one has a diagram (hard copy or on a separate monitor) plus tools such as Notepad++ to compare/highlight areas in configs.

  26. gui
    January 16th, 2020

    “how to dhcp” is slightly wrong!

    “ip dhcp excluded-address 10.2.1.1 10.2.1.2” IS a range (In this case only for 2 addresses):
    R4(config)#ip dhcp excluded-address ?
    A.B.C.D Low IP address
    R4(config)#ip dhcp excluded-address 10.2.1.1 ?
    A.B.C.D High IP address

    The rest is correct. Thank you.

    In Packet Tracer Sim, the range at R4 is “ip dhcp excluded-address 10.2.1.1 10.2.1.253”. In Fact all addresses are excluded since “ip dhcp excluded-address 10.2.1.254” is also configured on R4.
    In Packet Tracer Sim the ip-helper address at vl10 on DSW1 is correct. I guess in real Exam you should check both just to make sure.

  27. Majid
    January 18th, 2020

    In GNS3 topology, sometimes you cannot get the IP address from DHCP server (R4) even after the rectification of IP-Helper address on DSW-1. The solution is to restart the VLAN 10 interfce on DSW-1 and try to get an IP from Client-1 after that.

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