Q. While P-CSCF is resolving a DNS request for I-CSCF, and Site 1 is down, how will the traffic be distributed?
Received DNS priorities and weights:
- Site 1: priority 10, weight 100
- Site 2: priority 20, weight 50
- Site 3: priority 20, weight 50
- Site 4: priority 30, weight 100
If Site 1 is down, how will the traffic be distributed?
a) The traffic will go to Site 4
b) The traffic will be distributed equally on all sites
c) 100 percent of the traffic will go to Site 2
d) 50 percent of the traffic will go to Site 2 and other 50 percent will go to Site 3
Check π
Correct answer: Letter d.
In DNS-based service discovery (such as SIP/IMS), lower priority is preferred. Among records with the same priority, traffic is distributed based on weight.
After Site 1 (priority 10) is removed, the remaining sites are:
- Site 2: priority 20, weight 50
- Site 3: priority 20, weight 50
- Site 4: priority 30, weight 100
The resolver will choose only among the lowest remaining priority, which is priority 20 (Site 2 and 3). Their weights are equal (50 each), so traffic is evenly distributed between them.
Q. While P-CSCF is resolving a DNS request for I-CSCF, and Site 1 is down, how will the traffic be distributed?
a) The traffic will go to Site 4
β Incorrect. Site 4 has higher priority (30) than Sites 2 and 3, so it wonβt be selected unless all lower-priority sites are down.
b) The traffic will be distributed equally on all sites
β Incorrect. DNS prioritization restricts selection to the lowest available priority group (priority 20 in this case), not all sites.
c) 100 percent of the traffic will go to Site 2
β Incorrect. Site 2 and 3 have equal priority and weight, so traffic will be load balanced.
d) 50 percent of the traffic will go to Site 2 and other 50 percent will go to Site 3
β Correct. With equal priority and weight, RFC 2782 dictates the load is split based on weight within the same priority group.
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