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  • 1.  DHCP issue with a /21 network

    Posted 27 days ago

    I have a EX4600 VCP and running forwarding-options dhcp-relay on the irb.  So the issue I am experiencing is when the irb network is set to /21, the dhcp-relay doesnt work and no devices are getting an ip addess from the Windows DHCP server.  If I set the irb network to /22, /23, or /24, the forwarding-options dhcp-relay is working and devices are getting an ip address from the Windows DHCP server.  I am running Junos OS 20.4R3.8.  Has anyone run into this isssue.  Here is the command I am running.  JTAC is stump and not sure what is going on.

    set interfaces irb unit 450 family inet address 10.32.9.200/21
    set forwarding-options dhcp-relay group DHCP_CLIENT interface irb.450
    set vlans Guest-Wifi vlan-id 450
    set vlans Guest-Wifi l3-interface irb.450



  • 2.  RE: DHCP issue with a /21 network

    Posted 27 days ago

    The description suggests that this is a software bug known as PR (Problem Reports) in the Junos world.

    Looking at the public database search for EX and the Junos version does not seem to have any current matching bugs.

    https://prsearch.juniper.net/home?stype=affectingthis&ostype=junos&sid=EXSeries-junos&bv=20.4R3-S8&uv=&qt=dhcp

    This would mean it is either still in the internal only phase or not yet reported.  For these you will need to open an official support ticket to either find out the current status and fixed version for upgrade or register the bug for a fix.

    https://supportportal.juniper.net/s/



    ------------------------------
    Steve Puluka BSEET - Juniper Ambassador
    IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP - Retired)
    http://puluka.com/home
    ------------------------------



  • 3.  RE: DHCP issue with a /21 network

    Posted 18 days ago

    My post was not submitted, too elaborate??? Here is the short version:

    1: Why a /21? Can you make it several /22 or /23 instead? Nornally, a /21 contains way too many hosts.

    2: Can you upgrade to 21.4-R3-Sx?

    3: If this is indeed a bug and you can tweak things, do things like adding a secondary IP on the VLAN/IRB, replacing the VLAN tag or other stuff that may "break the bug".

    4: Can you keep one VLAN (450) but add several /24 IPs on the same IRB? this will only cause a change in the DHCP server, which is easy. This may (if you're lycky) eliminate the bug and get you a slightly more sane subnet structure until you can segment it into several VLANs.




  • 4.  RE: DHCP issue with a /21 network

    Posted 18 days ago

    1: Why a /21 subnet? Unless this is a BNG controlled subscriber network with split horizon or private VLAN, a /21 means trouble! Can you divide it into several /24 instead? Another approach (not as good, but...) is to have one VLAN but several IP addresses on it, like:

    set interfaces irb unit 450 family inet address 10.32.0.1/24

    set interfaces irb unit 450 family inet address 10.32.1.1/24

    set interfaces irb unit 450 family inet address 10.32.2.1/24

    2: If this is indeed a bug, chances are you can circumvent it by trying a different VLAN ID, subnet mask, DHCP server address or similar. Whatever is easy to change, change it! I have been around long enough to see things like this before. Add a /32 static route to your DHCP servers just to try!

    3: Why old Junos 20.4R3 and no -Sx-release? This is the recommendation right now: "Latest 21.4R3-Sx". I do understand that upgrading may not always be an option, but if you can, just do it! I'd even try 22.2R[latest]-S[latest] if 21.4 won't work.