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Home > Success Center > Netflow Traffic Analyzer (NTA) > NTA 4.2.3 Administrator Guide > High Availability in SolarWinds products > Which IP address is used as the source?

Which IP address is used as the source?

Updated: 12-1-2016

Outbound communication from the HA pool, such as WMI or SNMP polling requests, may be sent by the primary or secondary server's IP address or the VIP address. All inbound communication goes through the VIP address.

The active pool member has a minimum of two IP addresses available: the IP address of the server and the VIP address for the pool.

Because there are multiple IP addresses bound to a single NIC, Windows chooses which IP address is used as the originating IP address. The IP address with the most high order bits that match the destination of the next hop is used as the source IP address for all outbound polling activity.

You can determine the source IP address by doing the following:

  1. Convert the IP addresses to binary.
  2. From left to right, compare how many bits in the IP addresses match the default gateway's IP address.

The IP address with the most consecutive, matching bits is used for the HA pool's source IP address.

Choose an IP address close to the default gateway's IP address so outbound communication comes from the VIP address. You can also modify the converted bits to be the IP address with the longest match and convert it back to an IP address.

Examples of matching the binary bits

The following is an example where the VIP is used as the outbound IP address.

  IP address IP address converted to binary # of matching bits
Default Gateway (first hop) 10.199.15.1 00001010-11000111-00001111-00000001  
VIP 10.199.15.20 00001010-11000111-00001111-00010100 27
Primary pool member 10.199.15.61 00001010-11000111-00001111-00111101 26
Secondary pool member 10.199.15.62 00001010-11000111-00001111-00111110 26

The longest match in the example above is the VIP. It has 27 consecutive matching high order bits to the default gateway.

The following is an example where pool members' IP addresses are used as the outbound IP address.

  IP address IP address converted to binary # of matching bits
Default Gateway (first hop) 10.199.15.1 00001010-11000111-00001111-00000001  

VIP

10.199.15.82 00001010-11000111-00001111-01010010 25
Primary pool member 10.199.15.61 00001010-11000111-00001111-00111101 26
Secondary pool member 10.199.15.62 00001010-11000111-00001111-00111110 26

In this example, the longest match is the pool members' IP addresses. When a failover occurs, the IP address of the active Orion server is used as the source IP for all polling requests. The VIP address is only used for inbound traffic, such as syslog, SNMP traps, NetFlow, and accessing the Orion Web Console.

 
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