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Description of problem:

In lldp/agent.c clean_lldp_agents(), the function always sends a shutdown frame without checking if the daemon is in 'receive-only' mode. 

This causes problems with network switches, making them unavailable for several minutes.

Version-Release number of selected component (if applicable): RHEL 7.4


How reproducible: 100%


Steps to Reproduce:
1. Start lldpad in receive-only mode.
2. Halt lldpad, observe shutdown frames being sent on network.
3.

Actual results: Switches spend several minutes reconfiguring, interrupting network flow.


Expected results: Switches should not see shutdown frame and should continue running uninterrupted.


Additional info:

    diff --git a/lldp/tx.c b/lldp/tx.c
    index 1b95208..fb75f40 100644
    --- a/lldp/tx.c
    +++ b/lldp/tx.c
    @@ -332,6 +332,10 @@ void process_tx_idle(UNUSED struct lldp_agent *agent)
     
     void process_tx_shutdown_frame(struct port *port, struct lldp_agent *agent)
     {
    +       if (agent->adminStatus != enabledRxTx &&
    +           agent->adminStatus != enabledTxOnly) {
    +               return;
    +       }
            if (agent->timers.txShutdownWhile == 0) {
                    if (mibConstrShutdownLLDPDU(port, agent))
                            txFrame(port, agent);

Proposed patch to prevent sending the shutdown frame.

The proposed patch isn't good enough.  We need to actually do the check for a state transition.  Basically, when we transition
the port from rxtx to rxonly, then we also need to transmit the final ttl=0 value to purge remote endpoints.

Still, I think it's doable in the tx.c code, since the state transitions are tracked there.

https://github.com/intel/openlldp/pull/69 sent upstream.

This will not be resolved as part of RHEL7