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Livius's avatar
Livius
Icon for Cirrus rankCirrus
Nov 02, 2016

Weight Vs Score for Topology Records

Hi community! I am getting confused by the the terms weight vs score that can be associated to topology records. As I understand them, they should mean the same thing, however, in some documentation I have the following explanation :

is not

Weight (score)

The weight specifies the score that will be given to a destination object which matches the topology record. In the event that a name resolution request matches more than one topology record, the BIG-IP DNS system uses the destination object with the highest weight to determine which statement it uses to load balance the request.

whereas in some other resources I am getting other explanations:

If the type of LDNS request source statement is the same in multiple topology records and the type of destination statement is the same in those records, the system then uses the value of the weight from lowest to highest to sort the records.

So, which one is true?

Both statements are taken from either support or askf5 websites...

Thanks in advance.

application delivery
BIG-IP DNS

2 Replies

  • Jinshu's avatar
    Jinshu
    Icon for Cirrus rankCirrus
    Nov 02, 2016

    Both statements says the same thing...

    When you configure topology records, you will be asked to give weight for that record. This is to give the precedence to the records if duplication exists. In tmsh, the weight parameter is called score.

    For example, Consider below topology records,

    ldns: subnet 192.168.0.0/16  destination: London weight 100
ldns: subnet 192.168.0.0/16  destination: Spain weight 200

    These topology record have same LDNS and F5 BIG IP selects the topology based on lowest weight. That means BIG IP uses the London as destination.

    Hope this helps.

    -Jinshu

  • crodriguez's avatar
    crodriguez
    Ret. Employee
    Nov 02, 2016

    The terms "weight" and "score" are synonymous. "Weight" is used in the Configuration utility (GUI) and "score" is used in TMSH. But they refer to the same thing.

     

    During name resolution, the weight/score is a value that is given to the destination object in the topology record when the request source matches. (See below for more on the matching process). In the event of multiple matches, BIG-IP DNS uses the destination object with the greatest weight/score to load balance the query to.

     

    Keep in mind that, when using topology load balancing at either the wide IP or pool level, BIG-IP DNS only searches those topology records that are applicable to that wide IP or pool. Also, you have to take into consideration whether Longest Match is enabled or not. (It is by default.) In most cases, a set of topology records define mutually exclusive LDNS sets (request sources) so that the decision is clear. But when the set of topology records contains overlapping DNS, it is important to know the details of the systems' matching process. (I won't go into that here...)

     

    The net takeaway though is this: In the event the matching process produces more than one topology record match, the destination object with the highest weight/score is the object the query will be load balanced to.