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Peer DNS Address Resolution

The SBC Core supports defining a Diameter Peer by its IP address or using the Fully Qualified Domain Name (FQDN). In the latter case, the actual address is resolved through Domain Name System (DNS) queries. For each Diameter peer FQDN IP address resolution, the SBCgenerates a maximum sequence of DNS query types: NAPTR, SRV, and A/AAAA. Depending on the FQDN prefix configuration, each Trunk Group is assigned a Policy and Charging Rule Function (PCRF) realm (pcrfRealm) with matching Diameter realm route. Traffic generated on these Trunk Groups is directed to the peers in their corresponding realm route. Similarly, DNS address resolution is directed to the Trunk Group's DNS server group with the same realm assignment.

DNS Query


Multiple IP Connections per Peer

The SBC supports multiple IP connections per Diameter Peer. If a set of IP addresses are returned, the SBC connects to all IP addresses under the same peer. The parameter, sessionDistribution, handles the session distribution order.   

The SBC Diameter capacity for this feature is as follows:

Table 1: SBC Diameter capacity

ParameterMaximum
Capacity
Diameter Node1
Diameter Peers per Node10
Diameter Realm Routes per Node10
IP Connections per Peer10
SRV Records Processed5
Maximum Diameter Peer Connections (system-wide)32
  • IP connections (per peer) connect to the first 10 A/AAAA queried IP addresses, and the rest are ignored.
  • SRV records process top five priority/weight records, and the rest are ignored.


Load Balancing Support Across Peers

Load Balancing for Static Peer

When using load balancing with a static peer configuration (when no DNS query is made and IP address is configured on the peer), the realmRoute configured for each peer must have the same priority to distribute the load evenly among all configured peers.

The example below demonstrates three peers with each peer associated with a realmRoute.

ObjectConfiguration

peer d1

state enabled; ipAddress 10.7.6.40; fqdn d1.sbxlabsip.com; tcpPort 3866; deviceWatchdogTimer 20000

realmRoute r1

peer d1; priority 1; realm sonusnet.com; appId rx; state enabled



peer d2

state enabled; ipAddress 10.7.6.40; fqdn d2.sbxlabsip.com; tcpPort 3867; deviceWatchdogTimer 20000

realmRoute r2

peer d2; priority 1; realm sonusnet.com; appId rx; state enabled



peer d3

state enabled; ipAddress 10.7.6.40; fqdn d3.sbxlabsip.com; tcpPort 3868; deviceWatchdogTimer 20000

realmRoute r3

peer d3; priority 1; realm sonusnet.com; appId rx; state enabled

To exclude the peer from the load sharing. the corresponding realmRoute must be disabled (i.e to exclude peer d2 from load sharing, disable the realmRoute (realmRoute r2) associated with peer d2.

When realmRoute r2 is disabled, the load is evenly shared between d1 and d3.

Load Balancing for Dynamic Peer

For dynamic peer configuration (when DNS query is made to find the PCRF IP peer) and the SRV query results in multiple A records. To evenly distribute load among all peers, the peer sessionDistribution (addressContext default diamNode myDiamNode peer sessionDistribution) should be set to “round-robin”.

If one of the peer is down, the load gets automatically distribute among the remaining peers.


For configuration details, refer to:

EMA: Diam Node - Peer, Diam Node - Diam Peer Status

CLI: Diameter Node - CLI


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