[Kea-users] option 54 in subnet definition

Francis Dupont fdupont at isc.org
Fri Dec 16 09:45:10 UTC 2016


We know the address given is server-identifier should get more control,
there are some tickets about this (and as far as I know no time to
deal with them soon...).

Regards

Francis Dupont <fdupont at isc.org>
Igor Smitran writes:
> Hi list,
> 
> Did any of you tried to set custom server-identifier in a subnet?
> 
> In case you wonder why would one do that:
> 
> Server is in a private network, behind firewall. There is a dhcp relay 
> that forwards all requests to dhcp server.
> 
> But, when server leases a public ip to a cpe device then cpe device is 
> not able to renew it's lease because it is not able to send unicast 
> packet to dhcp server private ip.
> 
> Here comes ASA to rescue. There is a NAT on a public ip that forwards 
> all dhcp packets to private ip of dhcp server.
> 
> So, DHCP server needs to change his server-identifier in order to tell 
> the client that he can renew his lease by using public ip.
> 
> But, this doesn;t work, server still sends his private IP in option 54.
> 
>      {    "subnet": "PUBLIC/26",
>           "renew-timer": 300,
>           "rebind-timer" : 525,
>           "pools": [ { "pool": "FIRST_PUBLIC_IP - LAST_PUBLIC_IP" } ],
>           "option-data" : [
>           {
>             "name" : "dhcp-server-identifier",
>             "code" : 54,
>             "space" : "dhcp4",
>             "csv-format" : true,
>             "data" : "PUBLIC_IP_ASA_NAT"
>           },
> 
> ...
> 
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