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How does the NIOS device remember the IP for a past lease

Guru
Posts: 188
5918     0

Hi;

 

When granting a DHCP lease to a client say 10.10.10.1, say this same client comes back next day, requests a lease and get the same IP address if possible. How does the NIOS device remeber that this client with this MAC address should get 10.10.10.1? is there a memory table somewhere? if yes, how long is that memory and is it configurable?

 

 

Kindly

Wasfi

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Re: How does the NIOS device remember the IP for a past lease

Expert
Posts: 81
5919     0

Hello Wasfi,

 

As far as I know, the client itself will try to request the same IP address provided before by DHCP Server.

 

The item 4.4.1 in the DHCP RFC 2131 says (in the DHCPDISCOVER moment):

 

   The client MAY request specific parameters by
   including the 'parameter request list' option.  The client MAY
   suggest a network address and/or lease time by including the
   'requested IP address' and 'IP address lease time' options. 

 However, even if the client requests for a specific IP from DHCP, it up to the DHCP to provide (or not) the IP address requested by the client, so this type of "static allocation" must not be taken for granted.

 

Infoblox do maintains a log of all leases provided to clients, but I do not think it is configurable.

 

Hope this helps!

Paulo Costa

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Re: How does the NIOS device remember the IP for a past lease

Adviser
Posts: 200
5919     0
There is a lease table that contains all of the assignments of IPs to DHCP clients. If the same client comes back (whether it requests the same IP or not), the DHCP will “reuse” the previously assigned IP for that specific host and reissue the address. Any IP that is issued will only be reused for OTHER clients after all “free” / “never before assigned” addresses are handed out and then only in the order based on last time the address was issued.

This helps to ensure some level of consistency with IP assignment from the DHCP server. This is very common behavior for all DHCP platforms.
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Re: How does the NIOS device remember the IP for a past lease

Guru
Posts: 188
5919     0

Thank you Paulo. The log of leases I think is used with the historical leases report as opposed to current leases.

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Re: How does the NIOS device remember the IP for a past lease

[ Edited ]
Guru
Posts: 188
5919     0

Thank you DSmith. BTW, is this table located in the memory, which means that it gets flushed if the system is restarted?

 

Also, is this table time related. i.e. does an entry in it time out after a certain time, or it's that the entries in it just get updated without any relation to time. If it is time related is the entry expire time configurable. My guess is that entries in this table are independent of time.

 

 

Kindly

Wasfi

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