Significance of different TTL values in mDNS Resource Records and which TTL value controller uses

MVP Expert
MVP Expert
Q:

What is the significance of different TTL values in mNDS Resource Rrecords - SRV, TXT, PTR and Cache?



A:
  1. As a general rule, the recommended TTL value for Multicast DNS resource records with a host name as the resource record's name (e.g., A, AAAA, HINFO) or a host name contained within the resource record's rdata (e.g., SRV, reverse mapping PTR record) SHOULD be 120 seconds.
  2. The recommended TTL value for other Multicast DNS resource records is 75 minutes.
  3. Aruba controller updates the TTL value of the Airgroup server depending on the A record (IPV4) and AAAA record (IPv6) in the mDNS response packets from Airgroup server.
  4. As per RFC, controller need to send query for PTR record before the Airgroup cache expires. For any PTR record request the Airgroup server has to respond PTR, SRV, TXT, A and AAAA record.  

 

  • TTL values of A record is 120 second – Sent by Airgroup server (Printer, Apple TV, etc)
  • TTL value of other records 4500 – Sent by the Airgroup Server (Printer, Apple TV, etc)

 

(SAN-MM) [md] #show airgroup cache entries | include fec6:61ab

_http._tcp.local                                                 PTR         IN     4500  fe80::4a0f:cfff:fec6:61ab  3838.24  Tue Nov 27 02:41:34 2018

_printer._tcp.local                                              PTR         IN     4500  fe80::4a0f:cfff:fec6:61ab  3625.60  Tue Nov 27 02:41:34 2018

_http-alt._tcp.local                                             PTR         IN     4500  fe80::4a0f:cfff:fec6:61ab  3954.27  Tue Nov 27 02:41:34 2018

DEVC661AB.local                                                  A           IN     120   fe80::4a0f:cfff:fec6:61ab  662.33   Tue Nov 27 02:41:34 2018

DEVC661AB.local                                                AAAA        IN     120   fe80::4a0f:cfff:fec6:61ab  797.60   Tue Nov 27 02:41:34 2018

HP LaserJet Pro MFP M126nw[C661AB]._pdl-datastream._tcp.local  SRV/NBSTAT  IN     120   fe80::4a0f:cfff:fec6:61ab  653.49   Tue Nov 27 02:41:34 2018

HP LaserJet Pro MFP M126nw[C661AB]._http._tcp.local            TXT         IN     4500  fe80::4a0f:cfff:fec6:61ab  3695.81  Tue Nov 27 02:41:34 2018

HP LaserJet Pro MFP M126nw[C661AB]._printer._tcp.local         SRV/NBSTAT  IN     120   fe80::4a0f:cfff:fec6:61ab  727.08   Tue Nov 27 02:41:34 2018

HP LaserJet Pro MFP M126nw[C661AB]._ipp._tcp.local             SRV/NBSTAT  IN     120   fe80::4a0f:cfff:fec6:61ab  684.10   Tue Nov 27 02:41:34 2018

Soho-TKTS(AirPrint)._printer._tcp.local                      TXT         IN     4500  138.72.236.229             3954.61  Tue Nov  6 13:24:09 2018

_universal._sub._ipp._tcp.local                              PTR         IN     4500  138.72.236.229             3644.30  Tue Nov  6 13:24:09 2018

 

Aruba controller uses A/AAAA record to update the Airgroup cache. 

 

Version history
Revision #:
2 of 2
Last update:
2 weeks ago
Updated by:
 
Labels (1)
Contributors
Search Airheads
cancel
Showing results for 
Search instead for 
Did you mean: