Blocked ports with older devices

Some older devices are limited to four ports in a trunk. When eight LACP-enabled ports are connected to one of these older devices, four ports connect, but the other four ports are blocked. The LACP status of the blocked ports is shown as "Failure."

If one of the other ports becomes disabled, a blocked port replaces it (Port Status becomes "Up"). When the other port becomes active again, the replacement port goes back to blocked (Port Status is "Blocked"). It can take a few seconds for the switch to discover the current status of the ports.

Blocked ports with LACP

switch(eth-B1-B8)# show lacp


  PORT   LACP      TRUNK   PORT     LACP      LACP
  ----   -------   ------  ------   -------   ------
  B1     Active    Dyn1    Up       Yes       Success
  B2     Active    Dyn1    Up       Yes       Success
  B3     Active    Dyn1    Up       Yes       Success
  B4     Active    Dyn1    Up       Yes       Success
  B5     Active    Dyn1    Blocked  Yes       Failure
  B6     Active    Dyn1    Blocked  Yes       Failure
  B7     Active    B7      Down     No        Success
  B8     Active    B8      Down     No        Success

If there are ports that you do not want on the default VLAN, ensure that they cannot become dynamic LACP trunk members. Otherwise a traffic loop can unexpectedly occur. For Example:

Figure 14: A dynamic LACP trunk forming in a VLAN can cause a traffic loop

Easy control methods include either disabling LACP on the selected ports or configuring them to operate in static LACP trunks.