This chapter describes how to identify and resolve problems related to private VLANs.
Information About Private VLANs
Private VLANs (PVLANs) are used to segregate Layer 2 Internet service provider (ISP) traffic and convey it to a single router interface. PVLANs achieve device isolation by applying Layer 2 forwarding constraints that allow end devices to share the same IP subnet while being isolated at Layer 2. In turn, the use of larger subnets reduces address management overhead. Three separate port designations are used. Each has its own unique set of rules that regulate each connected endpoint's ability to communicate with other connected endpoints within the same private VLAN domain.
Private VLAN Domain
A private VLAN domain consists of one or more pairs of VLANs. The primary VLAN makes up the domain; each VLAN pair makes up a subdomain. The VLANs in a pair are called the primary VLAN and the secondary VLAN. All VLAN pairs within a private VLAN have the same primary VLAN. The secondary VLAN ID is what differentiates one subdomain from another.
Spanning Multiple Switches
Private VLANs can span multiple switches, just like regular VLANs. Inter-switch link ports do not need to be aware of the special VLAN type and can carry frames tagged with these VLANs just as they do with any other frames. Private VLANs ensure that traffic from an isolated port in one switch does not reach another isolated or community port in a different switch even after traversing an inter-switch link. By embedding the isolation information at the VLAN level and by transporting it with the packet, it is possible to maintain consistent behavior throughout the network. Therefore, the mechanism that restricts Layer 2 communication between two isolated ports in the same switch also restricts Layer 2 communication between two isolated ports in two different switches.
Private VLAN Ports
Within a private VLAN domain, there are three separate port designations. Each port designation has its own unique set of rules that regulate the ability of one endpoint to communicate with other connected endpoints within the same private VLAN domain. The following are the three port designations:
For additional information about private VLANs, see the Cisco Nexus 1000V for Microsoft Hyper-V Layer 2 Switching Configuration Guide.
Follow these guidelines when troubleshooting private VLAN issues:
- Verify that a private VLAN is configured correctly by entering the show vlan private-vlan command.
- Verify that the interface is up by entering the show interface slot-port command.
- Verify that the VEM is configured correctly by entering the module vem module-number execute vemcmd show port command.
Private VLAN Troubleshooting Commands
You can use the commands in this section to troubleshoot problems related to private VLANs.
To verify that a private VLAN is configured correctly, enter this command:
n1000V# show vlan private-vlan
Primary Secondary Type Ports
------- --------- --------------- -------------------------------------------
To verify if a physical Ethernet interface in a private VLAN trunk promiscuous mode is up, enter this command:
n1000V# show interface eth3/4
Hardware: Ethernet, address: 0050.565a.ca50 (bia 0050.565a.ca50)
Port-Profile is DATA-Macpin
MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,
reliability 0/255, txload 0/255, rxload 0/255
Port mode is Private-vlan trunk promiscuous
158776 Input Packets 75724 Unicast Packets
76 Multicast Packets 82976 Broadcast Packets
75763 Output Packets 75709 Unicast Packets
3 Multicast Packets 51 Broadcast Packets 0 Flood Packets
5507 Input Packet Drops 0 Output Packet Drops
To verify if a virtual Ethernet interface in private VLAN host mode is up, enter this command:
n1000V# show interface v3
Port description is fedora9
Hardware is Virtual, address is 0050.56bb.6330
Owner is VM "fedora9", adapter is Network Adapter 1
Port-Profile is pvlancomm153
Port mode is Private-vlan host
14802 Input Packets 14539 Unicast Packets
122 Multicast Packets 141 Broadcast Packets
15755 Output Packets 14492 Unicast Packets
0 Multicast Packets 1263 Broadcast Packets 0 Flood Packets
45 Input Packet Drops 0 Output Packet Drops
To verify if a VEM is configured correctly, enter this command:
n1000V# module vem 3 execute vemcmd show port
LTL VSM Admin Link State PC-LTL Vlan SG_ID Vem Port Type
8 Eth3/1 UP UP UP 305 3969 2
9 Eth3/2 UP UP UP 305 3969 2
10 Eth3/3 UP UP UP 306 150 2
11 Eth3/4 UP UP UP 306 3968 2
12 Eth3/5 UP UP UP 306 151 2
14 Veth33 UP UP UP 0 3967 2
16 Veth34 UP UP UP 0 1 T 2
- module vem module-number execute vemcmd show port
If additional information is required for Cisco Technical Support to troubleshoot a private VLAN issue, use the following commands:
- s how system internal private-vlan info
- show system internal private-vlan event-history traces