Administrator Guide

This section covers the enhancements to this feature based on scenarios in Dell Networking OS 9.11.2.0:
Loop caused due to mis-cabling across PEs or within a PE
● Two PE interfaces PEX1 and PEX2 are looped back wrongly due to mis-cabling.
● Both the interfaces are assigned to a VLAN which is assigned an IP address.
A simple ping for an IP address in the subnet will result in a continuous loop without being detected. The reason being we don’t
learn our own MAC address and hence, the MAC station move is never detected. Without station moves, the existing PE Loop
Detection Feature would not kick-in. If there is no data traffic on the LAN to detect the loop, the control PDUs like LACP, LLDP,
ARP, DHCP etc., will be used to detect loops at PE.
● At kernel, the following validations are done:
○ Any control PDU (LACP or LLDP or ARP or DHCP etc) received at CB will be first checked for the source MAC address
against matching any one of its PEX interface address.
○ In this scenario the source MAC could be the system MAC and in this case, the receiving PE interface would be brought
down to cut the loop.
● If there is a match, the kernel notifies L2Mgr about the loop detection and L2Mgr would in turn, bring down the appropriate
PE interface and show an appropriate syslog to the user to correct the loop.
Loop caused due to mis-cabling in an un-managed L2 switch
● An un-managed layer 2 switch is connected to a PE.
● There is some mis-cabling in the L2 switch.
This can result in loops. The current PE loop detection mechanism with data traffic MAC station move, can possibly bring down
the other PE interface which is not connected to the L2 switch, thereby keeping the loop active.
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Port Extenders (PEs)