DNS Question

neathneathneath

If a secondary DNS server (with standard zones) is offline for a while and gets out of date with other servers, which option takes the biggest hit on the network?

a) Reload from Master

b) Transfer from master

I would guess at (b) but could someone please confirm the correct option.

undomiel

It depends upon how stale the data on the secondary is. When you do a reload from master the server wipes the zone and does a complete (AXFR) zone transfer from the primary. When you do a transfer from master then the server attempts an incremental transfer (IXFR) by checking the SOA and comparing serial numbers. Of course this will tell it that its out of date and needs to update. The primary server then checks its log of incremental updates and transfers over only the changes. That makes transfer a lighter load. This works peachy unless the secondary has been out of commission too long and the logs don't go back that far. Then an AXFR transfer will occur. In that case transfer or reload will both generate about the same amount of traffic. For more info on zone transfers check here: Understanding zones and zone transfer: Domain Name System(DNS)

neathneathneath

undomiel wrote: »

It depends upon how stale the data on the secondary is. When you do a reload from master the server wipes the zone and does a complete (AXFR) zone transfer from the primary. When you do a reload from master then the server attempts an incremental transfer (IXFR) by checking the SOA and comparing serial numbers. Of course this will tell it that its out of date and needs to update. The primary server then checks its log of incremental updates and transfers over only the changes. That makes transfer a lighter load. This works peachy unless the secondary has been out of commission too long and the logs don't go back that far. Then an AXFR transfer will occur. In that case transfer or reload will both generate about the same amount of traffic. For more info on zone transfers check here: Understanding zones and zone transfer: Domain Name System(DNS)

thanks for the reply but you seem to have mentioned "reload from master" twice so i'm none the wiser

undomiel

That's what I get for posting just before going to bed, sorry about that! The IXFR attempt comes from a transfer from master, not from a reload from master.