Alexander, it is the same link....clearly, but reversed. The second one is marked status "N" not active, in any case this seems to be a bug, because
the QueryManager should manage this.
I have reviewed linkd a lot in the path months, and I'm sure also I reviewed the persisting part....but the changes are in master.

I'll take a look at the code in 1.12.

Here's output from the DB underpinning the threading idea:

opennms=# SELECT * from datalinkinterface where ifindex in (10008,10102);
nodeid | ifindex | nodeparentid | parentifindex | status | lastpolltime | id | linktypeid | source
------------------------------------------------------------------------------------------------------------ 2 | 10008 | 4 | 10102 | A | 2014-02-15 03:44:50.149+03 | 1894 | -1 | linkd
4 | 10102 | 2 | 10008 | N | 2014-02-14 22:44:49.498+03 | 1487 | -1 | linkd

Double link on Cisco 2960.

Here's another example for Cisco (2960 series, IOS 12.2(58)). Same scenario, there is RSTP and CDP available, as well as LLDP.

The links are basically the same link, but one is the reverse of the other (i.e. one is A->B, the other B->A, same interfaces invovled in both).

Could it be as simple as linkd running multiple threads and if thread A is working switch A and thread B works switch B at the same time, while there is a link A to B, then the code that inserts link data only checks if the exising link is A->B and not B->A?

There is SNMP to all switches, the switches run LLDP and RSTP.

linkd config:

<package name="net-mgmt" enable-vlan-discovery="true" enable-discovery-download="true">
<filter>IPADDR != '0.0.0.0'</filter>
<include-range begin="10.15.28.1" end="10.15.28.254"/>
<include-range begin="192.168.255.241" end="192.168.255.254"/>
</package>