Dns Servers

[Marcelo Magno Espindola de Melo]

How many dns servers can I configure for isc-dhcpd to serve?

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[Niall O'Reilly]

On 25 Nov 2016, at 12:17, Marcelo Magno Espindola de Melo wrote:

> How many dns servers can I configure for isc-dhcpd to serve?

  There is no specific limit.
  Beyond two or three, any additional ones are likely not useful.

  I'ld suggest just using two.

  I understand that some clients (used to?) ignore any DNS servers
  beyond the first two.

  It's  not unusual for clients to attempt to use the DNS servers
  always in the same order (as given in the DHCP option 6), so that
  the second one is only used in case a response is not received
  from the first within the time-limit.  If you configure 5 DNS
  servers, and for some reason only the last is working, your
  customers will notice such delays that they won't appreciate the
  trouble you took to provide four stages of fallback.

  Best regards,
  Niall O'Reilly
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[Bob Harold]

On Fri, Nov 25, 2016 at 8:00 AM, Niall O'Reilly <[hidden email]> wrote:

On 25 Nov 2016, at 12:17, Marcelo Magno Espindola de Melo wrote:

> How many dns servers can I configure for isc-dhcpd to serve?

  There is no specific limit.
  Beyond two or three, any additional ones are likely not useful.

  I'ld suggest just using two.

  I understand that some clients (used to?) ignore any DNS servers
  beyond the first two.

  It's  not unusual for clients to attempt to use the DNS servers
  always in the same order (as given in the DHCP option 6), so that
  the second one is only used in case a response is not received
  from the first within the time-limit.  If you configure 5 DNS
  servers, and for some reason only the last is working, your
  customers will notice such delays that they won't appreciate the
  trouble you took to provide four stages of fallback.

  Best regards,
  Niall O'Reilly

There might be other clients that try all the addresses at the same time, so again two is the best number.

If I recall correctly, three was the limit at one point.  So three would also be ok.

Beyond that, use anycast (preferred) or a load balancer to put more DNS servers behind the same 2 or 3 IP's.

-- 

Bob Harold

 

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[Stier, Matthew]

I believe the limit on DHCP server side is unlimited.

 

However, different DHCP clients may have different limits.  Under Unix/Linux systems, the limit is usually 3 DNS servers, and 6 DNS search domains.

 

 

From: dhcp-users [mailto:[hidden email]] On Behalf Of Marcelo Magno Espindola de Melo
Sent: Friday, November 25, 2016 6:18 AM
To: [hidden email]
Subject: Dns Servers

 

How many dns servers can I configure for isc-dhcpd to serve?

 

===============
Atenciosamente, 
Marcelo Magno

 

 

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