Infoblox Exchange Cybersecurity Roadshow 2020 – Join us!
North America | Europe | Middle East/Africa | Asia-Pacific

DNS DHCP IPAM

Reply

DHCP server behavior when updating the DNS servers info in the DHCP options

ls01c
Techie
Posts: 2
4480     0

will the DHCP client wait till the IP release in order to get the latest updated DNS server IP addresses or is there a DHCP action from DHCP server to ask all the DHCP client to update their DNS server IP address.

Re: DHCP server behavior when updating the DNS servers info in the DHCP options

Adviser
Posts: 77
4480     0

I'm not 100% sure what you mean, but the client is always responsible for any DHCP action, the DHCP server will never send/ask something on it's own. When a renew takes place, it will use the newly obtained IP addresses of the DNS servers if these where changed. So for clients with a long leasetime, say 8 days, it can take upto 4 days before it uses the new IP addresses.

 

Re: DHCP server behavior when updating the DNS servers info in the DHCP options

ls01c
Techie
Posts: 2
4480     0

thanks Harrys for the reply. my question is, when an administrator change a DNS server settings in a DHCP scope, will all the clients inside that scope gets the new DNS server settings immediately or it will have to have till it's lease time expired to get the update.

Re: DHCP server behavior when updating the DNS servers info in the DHCP options

Adviser
Posts: 128
4480     0

Hello There,

 

That’s not going to be immediate. As what Harry mentioned, it’ll take half the configured lease period for the changes to take effect in clients if options(DNS servers) are updated on the server right after the initial lease. Keep in mind that the update would not be in effect unless & until you restart the DHCP service following the change. Ideally a client would send a renewal request which includes the parameter request list. The server would respond back to the request with the options specified in this list. As per the example from previous reply :

 

  • Say a client gets a lease for 8 days.

 

  • You update the DHCP options on the server by day 3(List of DNS servers).

 

  • As the client contacts the server the fourth day for lease renewal, the newly configured option(DNS servers) is returned to the client. So that means, the server is not going to push anything to the client, unless requested & it doesn’t wait for the lease to ‘expire’. To make it more clear, until the client contacts the server for lease renewal, it’ll continue to use the old DNS servers that you’ve configured.

 

Hope that’ll clarify your question.

 

Best regards,

Mohammed Alman.

 

Re: DHCP server behavior when updating the DNS servers info in the DHCP options

MisterFritchy
Techie
Posts: 3
4480     0

Hi Mohammed,

I'm in the same boat (I think) - I need to change some DNS servers from internal to external IPs.  If I do this, it will propogate at half the lease time, I understand that.  In the meantime though, will it cause traffic interruption or service impact to the subnet?

 

Thanks

-Ian

Highlighted

Re: DHCP server behavior when updating the DNS servers info in the DHCP options

TTiscareno Community Manager
Community Manager
Posts: 360
4480     0

@MisterFritchy wrote:

Hi Mohammed,

I'm in the same boat (I think) - I need to change some DNS servers from internal to external IPs.  If I do this, it will propogate at half the lease time, I understand that.  In the meantime though, will it cause traffic interruption or service impact to the subnet?

 

Thanks

-Ian


Changing DHCP options requires a service restart to take effect so yes, there will be a minimal service impact as the DHCP service restarts. This is generally fairly quick and most clients won't notice anything more than a hiccup as the restart takes place.

Showing results for 
Search instead for 
Do you mean 

Recommended for You