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DHCP relay - N3024 stack

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DHCP relay - N3024 stack

This question has been answered by DELL-Daniel C

Hello

I have problem in which these N3024  L3 core switches (stacked) don’t perform dhcp relay.

Having inherited this little network and not worked on Dells for long, I thought I would post here in view you may be able to say if I am looking at a buggy IOS or a simple config mistake.

Setup inverted U design:

                                     N3024 stack
                Dell N2048P stack       Cisco 2960x stack

This issue only came to our attention when the cisco stack had a power failure and the site then started failing dhcp allocation, when the power was restored to that cisco stack dhcp stated to work again for the whole site

For me it It’s unusual having to apply relay on any access switch as naturally they are just host switches,  and as it’s the L3 core( dell N300 in this case) where the L3 addresses for the vlans reside should where you need to be applying relay for the  dhcp servers. However in this instance once the relay was removed from the 8th floor cisco stack everything fails on both floors which replicated the previous power issue to the cisco stack.

 

 

Wireshark capture with the failed tests confirms no dhcp offer ever occurring and on the success tests shows proxy to the cisco stack

 

L3 core ( dell n3024 stack)
7th floor ( dell n2048 stack)
8th floor (cisco 2960x stack)


L3 and 7th-8th access closets – success for both floors ( because its applied to cisco )
L3 and 8th- access closet – success for both floors ( because its applied to cisco )

8th- access closet only - – success for both floors

L3 core only – fails for both floors
L3 and 7th- access closet – fails for both floors

7th access closets only - fails for both floors

I am fairly positive at this time it isn’t a configuration issue and tend to be thinking down the lines of a possible bug on the dell’s ios, but will need further investigation to confirm, hence this ticket to you guys.

res
Paul


 

Verified Answer
  • There have been some DHCP improvements over the various releases, and may be worth updating.

    The latest firmware is 6.3.2.7: http://dell.to/2vG9RlU

    If you can post up the config, we can help look through it. The output from the following command may help as well.

    console #show dhcp l2relay all

    console#show ip dhcp snooping

    Daniel Covey
    Dell EMC | Enterprise Support Services
    Get support on Twitter: @DellCaresPRO

    Download our QRL app: iOSAndroidWindows

  • I found a few older cases with similar DHCP issues. The two common fixes were a reboot, or firmware updates. If you are certain the config is good, I suggest looking at updating the firmware and testing again.

    Daniel Covey
    Dell EMC | Enterprise Support Services
    Get support on Twitter: @DellCaresPRO

    Download our QRL app: iOSAndroidWindows

All Replies
  • There have been some DHCP improvements over the various releases, and may be worth updating.

    The latest firmware is 6.3.2.7: http://dell.to/2vG9RlU

    If you can post up the config, we can help look through it. The output from the following command may help as well.

    console #show dhcp l2relay all

    console#show ip dhcp snooping

    Daniel Covey
    Dell EMC | Enterprise Support Services
    Get support on Twitter: @DellCaresPRO

    Download our QRL app: iOSAndroidWindows

  • Hello

    As requested, and FYI I noticed this L2relay feature and did apply globally and at interface level whist troubleshooting, but it didnt work, so at present it tunred off

    Dell L3 core

    show ver
    Machine Description............... Dell Networking Switch
    System Model ID................... N3024
    Machine Type...................... Dell Networking N3024
    Serial Number..................... CN0PDJ93282984950148A02
    Manufacturer...................... 0xbc00
    Burned In MAC Address............. F8B1.5654.2E38
    System Object ID.................. 1.3.6.1.4.1.674.10895.3057
    SOC Version....................... BCM56342_A0
    HW Version........................ 5
    CPLD Version...................... 13

    unit active      backup      current-active next-active
    ---- ----------- ----------- -------------- --------------
    1    6.1.2.4     6.1.2.4     6.1.2.4        6.1.2.4
    2    6.1.2.4     6.1.2.4     6.1.2.4        6.1.2.4

    show dhcp l2relay all
    DHCP L2 Relay is  Disabled.

    Interface   L2RelayMode    TrustMode
    ----------  -----------  --------------

    VLAN Id    L2 Relay    CircuitId    RemoteId
    --------- ----------  ----------- ------------

    #show ip dhcp  snooping
    DHCP snooping is Disabled
    DHCP snooping source MAC verification is disabled
    DHCP snooping is enabled on the following VLANs:


     Interface    Trusted     Log Invalid Pkts
    -----------  ----------   ----------------


    show ip dhcp  relay
    Maximum Hop Count.............................. 15
    Minimum Wait Time(Seconds)..................... 90
    Circuit Id Option Mode......................... Disable
    Circuit Id Option Check Mode................... Disable



    Dell access stack

    show ver

    Machine Description............... Dell Networking Switch
    System Model ID................... N2048P
    Machine Type...................... Dell Networking N2048P
    Serial Number..................... CN0H3MDW282984AK0461A02
    Manufacturer...................... 0xbc00
    Burned In MAC Address............. F8B1.565B.8028
    System Object ID.................. 1.3.6.1.4.1.674.10895.3056
    SOC Version....................... BCM56340_A0
    HW Version........................ 5
    CPLD Version...................... 13

    unit active      backup      current-active next-active
    ---- ----------- ----------- -------------- --------------
    1    6.1.2.4     6.1.2.4     6.1.2.4        6.1.2.4
    2    6.1.2.4     6.1.2.4     6.1.2.4        6.1.2.4
    3    6.1.2.4     6.1.0.6     6.1.2.4        6.1.2.4
    4    6.1.2.4     6.1.2.4     6.1.2.4        6.1.2.4

    show dhcp l2relay all

    DHCP L2 Relay is  Disabled.

    Interface   L2RelayMode    TrustMode
    ----------  -----------  --------------

    VLAN Id    L2 Relay    CircuitId    RemoteId
    --------- ----------  ----------- ------------

    show dhcp l2relay all

    DHCP L2 Relay is  Disabled.

    Interface   L2RelayMode    TrustMode
    ----------  -----------  --------------

    VLAN Id    L2 Relay    CircuitId    RemoteId
    --------- ----------  ----------- ------------

    show ip dhcp  snooping
    DHCP snooping is Disabled
    DHCP snooping source MAC verification is disabled
    DHCP snooping is enabled on the following VLANs:


     Interface    Trusted     Log Invalid Pkts
    -----------  ----------   ----------------

    #show ip dhcp  snooping

    DHCP snooping is Disabled
    DHCP snooping source MAC verification is disabled
    DHCP snooping is enabled on the following VLANs:


     Interface    Trusted     Log Invalid Pkts
    -----------  ----------   ----------------


    show ip dhcp relay
    Maximum Hop Count.............................. 15
    Minimum Wait Time(Seconds)..................... 90
    Circuit Id Option Mode......................... Disable
    Circuit Id Option Check Mode................... Disable


    res
    Paul

  • Can you show us your configuration? The ip helper part of the confguration should look similar to the following.

    console#config
    console(config)#interface vlan 10
    console(config-if-vlan10)#ip helper-address 10.10.1.1 dhcp
    The user guide has some config example on page 1232: http://dell.to/1WFiTWT
    The firmware looks to be quite outdated as well. http://dell.to/2vG9RlU

    Daniel Covey
    Dell EMC | Enterprise Support Services
    Get support on Twitter: @DellCaresPRO

    Download our QRL app: iOSAndroidWindows

  • Sorry left out a bit of the command line.

    console(config)# ip helper enable

    Daniel Covey
    Dell EMC | Enterprise Support Services
    Get support on Twitter: @DellCaresPRO

    Download our QRL app: iOSAndroidWindows

  • Hello

    It curently set below on both the dell L3 and L2 stacks
    int vlan xx
    ip helper-address x.x.x.x

    The current config is just with the server address applied, however this has also been tested with the dhcp protocol, both together and with and without the global dhcp l2relay and ip helper enable command even though the latter this is supposed to be enabled by default - None have been successful.

    Even tried with/without option 82 insertion, and with increased waiting times and nothing has worked

    As I stated, I even captured the dhcp traffic and with all these various settings and it did even get past the discovery, but when applied to a Cisco L2 access stack everything kicked in and the DORA's initiated be it via proxying the cisco L2 switch stack

    Do you have a related issue with this particular ios, I cannot seen to find any bug search tool like we have a cisco.


     
    res
    Paul

  • I found a few older cases with similar DHCP issues. The two common fixes were a reboot, or firmware updates. If you are certain the config is good, I suggest looking at updating the firmware and testing again.

    Daniel Covey
    Dell EMC | Enterprise Support Services
    Get support on Twitter: @DellCaresPRO

    Download our QRL app: iOSAndroidWindows

  • Hello Daniel

    TBH not even tried rebooting the stack, I'll  probaly give that a go first and then look inot a ios upgrade-

    cheers for the validation anyway

    res
    paul