Home > Ticket 13 – DHCP Helper-address

Ticket 13 – DHCP Helper-address

April 24th, 2018 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 (13) Comments
  1. 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”

  2. 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.

  3. 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.

  4. 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.

  5. Please help,
    February 3rd, 2020

    Taking exam in 2 days and trying to figure out the correct answer, I know about no exclude command but do we put in an ip exclude command..or is it on DSW1 rather than R4..any help will do please

  6. CR
    February 5th, 2020

    I passed the TSHOOT exam today. Got 1000. Nov 13th MCP/ HSRP and BGP Simlets /12 Labs from this website. All is here.

    Becarefull with the IP helper lab. Even though the port security is on fa1/0/1 and fa1/0/2, the interfaces on “show ip int brief” are up/up, the issue was ip helper on DSW1.

    I figured that out because of the status of the two access interfaces on ASW1.

    Good luck guys
    Thanks Networktut.

  7. Jenny_chey
    February 6th, 2020

    Passed 9XX/1000

    MY GAME PLAN

    -STUDY NULLZERO AND PING BY SAM
    -MEMORIZE NOV AND SEPT 2013 (Actually only 1Q appeared from sept)
    – Study HSRP and BGP (Both appeared on the exam)

    DONT LISTEN TO OTHER BULLSHIT that some had changed on the exam.

    P.S.

    There is 1 ticket that
    1. APIPA
    2. DHCP helper address is incorrect on DSW1
    3. Has Port Security on ASW1.

    I just answered DHCP helper can someone confirm if this is the correct answer or not?

    Thanks,
    Jen

    GOODLUCK GUYS!!!!

  8. buttmunch
    February 7th, 2020

    FYI you can still get an address because the client will use DSW2 to reach R4. Still, the correct answer for the *exam* will be changing the helper address on DSW1. If you don’t know what it us, just log into R4 and have a look to doublecheck

  9. Anon
    February 8th, 2020

    @Jenny_chey, it’s not bullshit that some changes are there. It appears as if Cisco has put in misleading clues, such as you mentioned. One ticket with APIPA and portsec, but port is not err-disable.

    The tickets are valid, but extra caution is needed to verify the correct ticket. Once you know the problem, the answer is still the same as here. But the difficulty is finding the correct problem ticket.

    -Anon

  10. 007
    February 9th, 2020

    Here is my approach:

    1) First verify the problem exist => unsuccessful ping from Client 1 to web server.
    2)Ping R4(10.1.4.5 or 6) – unsuccesful. Go to R4 and try to ping webserver and it is successful. Now I know the problem is before R4 so I go back adn start checking my interfaces for any L1 issues. I see all the interfaces are up/up so no L1 issues. Need to verify L2 and L3 connectivity from client 1 to gateway.
    3)Do a ipconfig on R1 and there is no gateway! Client 1 has APIPA meaning it cannot contact a DHCP server so it is auto configuring itself. Do a show run on the switches to check fr any DHCP leads

    4)On DSW1 and DSW2 we see there is an IP address helper command for vlan 10 and looking at the topology client 1 is on vlan 10

    5)DSW1 has an ip adress helper of 10.2.21.129 and DSW2 has an ip address helper of 10.2.1.129

    6)We need to find the interface having this ip on the connecting router R4
    On R4, issue sh ip int brief and Loopback 1 has an ip address of 10.2.1.129 so DSW1 has a wrong IP address

    Therefore the problem is on DSW and it is DHCP related. The solution is to delete the wrong ip helper address 10.2.2.129 and add the right ip helper address of 10.2.1.129

  11. Henry
    February 10th, 2020

    @007
    I think the right ip helper address should be 10.1.21.129?

  12. B-CCNP
    February 16th, 2020

    Hi Henry
    yes. my mistake. 3rd octet must be 21 always.
    correct IP helper is 10.1.21.129 got full marks for everything

  13. mgk
    February 18th, 2020

    @☻buttmuch clients will not be able to get ip addresses as the active interface in the hsrp group is on dsw1