Ethernet Switching
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Ethernet Switching

EX4300 DHCP Relay bindings

‎12-05-2017 09:57 AM

 I had anotther thread from a few days ago, but I have some more information now and want to ask a different question.

EX4300 VC on 14.1X53-D46.7 with mainly wireless clients. When the clients move around and connect to an access point on a different subnet than their previous one, the do not obtain a new IP address. Wireshark shows them making repeated requests (broadcast) that the server does not see.

I understand that then the DHCP relay see the ACK from the server, the creates a binding for that client (MAC address), and the IRB interface interface:

10.4.150.4   167   00:10:49:2c:a4:f1   151   BOUND   irb.1504

When the client moves and connectes to a different subent, the fact that this record exists prevents the switch from forwarding the DHCP Request braodcasts to the server. If I manually delete the binding, the server recieves the very next DHCP Request, and is able to reply with a NAK, prompting the client to immediatley start the DORA process and get an IP and a new binding.

 

How can I force the switch to discard/overwrite the old binding when the client attempts DHCP from a new subent, or disable the binding process all together if doing so allows clients to move around unhindered by 1-3 minutes of waiting for this record to age out?

 

I had no problem with DHCP on the EX4200s I took out less than 2 weeks ago.

root@Moatfield-VC> show configuration forwarding-options dhcp-relay
traceoptions { ## Warning: 'traceoptions' is deprecated
    file DHCPRELAY size 10m files 10;
    flag all;
}
forward-snooped-clients all-interfaces;
overrides {
    allow-snooped-clients;
    always-write-giaddr;
}
server-group {
    DHCP_Servers {
        10.1.100.66;
    }
    DHCP_Laptop {
        10.4.105.230;
    }
}
route-suppression {
    destination;
}
inactive: group DHCP_Interfaces {
    active-server-group DHCP_Servers;
}
group MC_DHCP_Interfaces {
    active-server-group DHCP_Laptop;
    interface irb.158;
    interface irb.1054;
    interface irb.1104;
    interface irb.1504;
    interface irb.2104;
    interface irb.2204;
    interface irb.2224;
    interface irb.2244;
    interface irb.2304;
    interface irb.2324;
    interface irb.2404;
}

{master:0}
3 REPLIES 3
Ethernet Switching

Re: EX4300 DHCP Relay bindings

‎12-05-2017 10:07 AM

Hi,

 

Did you tried below knob?

 

delete-binding-on-renegotiation

 

https://www.juniper.net/documentation/en_US/junos/topics/reference/configuration-statement/delete-bi...

 

Regards,

Rahul

Ethernet Switching

Re: EX4300 DHCP Relay bindings

[ Edited ]
‎12-05-2017 10:21 AM

Yes, I gave that a try but it did not help. I think because the documentaton states it is ment to tirgger on DHCP Discover packets. I have no problem getting an IP if the client starts with a Discover. Only an issue if they are sending "Request" broadcasts

Ethernet Switching

Re: EX4300 DHCP Relay bindings

‎12-11-2017 05:43 AM

I know someone who has reported same behavior.  Do you have a case open?  Do you have a packet capture of the Request [DHCP] packet?  If yes, please attach.