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dhcp packets not relayed to external dhcp server (helper-address not working)

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  • 1.  dhcp packets not relayed to external dhcp server (helper-address not working)

    Posted Feb 13, 2019 05:03 AM

    Hi,

     

    I've configured a vlan to send dhcp packets to an external server

    (momand) *[md] #show configuration effective detail santa | begin "interface vlan 107" 
    interface vlan 107                                                               # local [/md/epicerie/00:1a:1e:03:8f:30]
        ip address 192.168.107.253 255.255.255.0                                     # local [/md/epicerie/00:1a:1e:03:8f:30]
        ip helper-address A.B.C.D                                              # local [/md/epicerie/00:1a:1e:03:8f:30]

     

    when a client in this vlan ask for an IP address, all i have is:

     

    Feb 13 10:59:03 santa CEF:0|Aruba|A72xx|68230|log|SystemEvent|3|deviceProcessName=dhcpd dvcpid=22412 dvchost=santa msg=<299801> <22412> <DBUG> \|dhcpd\|  DHCPDISCOVER from ac:87:a3:0a:c9:1f via eth1: unknown network segment
    Feb 13 10:59:03 santa CEF:0|Aruba|A72xx|68230|log|SystemEvent|3|deviceProcessName=dhcpd dvcpid=22412 dvchost=santa msg=<299801> <22412> <DBUG> \|dhcpd\|  DHCPDISCOVER from ac:87:a3:0a:c9:1f via 192.168.107.253: unknown network segment

    and no packets are sent to the unicast A.B.C.D address.

     

    I'm fighting with this problem for days ...

    any idea ?

     

     

     



  • 2.  RE: dhcp packets not relayed to external dhcp server (helper-address not working)

    Posted Feb 13, 2019 05:07 AM

    More information:

    I use the internal dhcp server for another vlan

    (santa) #show ip dhcp database
    
    DHCP enabled
    
    # vlan_5
    subnet 192.168.4.0 netmask 255.255.252.0 {
    	option vendor-class-identifier  "ArubaAP";
    	option vendor-encapsulated-options  "xx.xx.xx.xx";
    	option domain-name-servers B.C.D.E;
    	option routers 192.168.5.254;
    	range 192.168.4.1 192.168.5.253;
    	range 192.168.5.255 192.168.7.254;
    	authoritative;
    } 

     



  • 3.  RE: dhcp packets not relayed to external dhcp server (helper-address not working)

    Posted Mar 06, 2019 08:21 AM

    No idea ?

     

    How could I debug the dhcp-relay (helper) process ?

     



  • 4.  RE: dhcp packets not relayed to external dhcp server (helper-address not working)
    Best Answer

    Posted Mar 08, 2019 10:48 AM

    Solved !

    A dhcp snooping bug in an HP 5900 switch in the middle :-(

     

    packet-capture was my best friend to find it ...