This chapter describes how to identify and resolve problems related to private VLANs.
This chapter includes the following sections:
•Information About Private VLANs
•Private VLAN Troubleshooting Commands
Information About Private VLANs
Private VLANs (PVLANs) are used to segregate Layer 2 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 Layer 2 isolated. In turn, the use of larger subnets reduces address management overhead. Three separate port designations are used, each having its own unique set of rules regulating 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; and 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 need not be aware of the special VLAN type and carry frames tagged with these VLANs just like they do 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 along with the packet, it is possible to maintain consistent behavior throughout the network. Therefore, the mechanism which 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 which 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 Layer 2 Switching Configuration Guide, Release 4.2(1)SV1(4).
Follow these guidelines when troubleshooting private VLAN issues:
•Use the show vlan private-vlan command to verify that a private VLAN is configured correctly.
•Use the show interface slot-port command to verify the interface is up.
•Use the module vem module-number execute vemcmd show port command to verify the VEM is configured correctly.
Private VLAN Troubleshooting Commands
Use the commands listed in this section to troubleshoot problems related to private VLANs.
To verify that a private VLAN is configured correctly, use the following command:
•show vlan private-vlan
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, use the following command:
Hardware: Ethernet, address: 0050.565a.ca50 (bia 0050.565a.ca50)
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
Auto-Negotiation is turned off
Input flow-control is off, output flow-control is off
Switchport monitor is off
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, use the following command:
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, use the following command:
•module vem module-number execute vemcmd show port
n1000V# module vem 3 execute vemcmd show port
LTL IfIndex Vlan Bndl SG_ID Pinned_SGID Type Admin State CBL Mode Name
8 0 3969 0 2 2 VIRT UP UP 4 Access l20
9 0 3969 0 2 2 VIRT UP UP 4 Access l21
10 0 150 0 2 2 VIRT UP UP 4 Access l22
11 0 3968 0 2 2 VIRT UP UP 4 Access l23
12 0 151 0 2 2 VIRT UP UP 4 Access l24
13 0 1 0 2 2 VIRT UP UP 0 Access l25
14 0 3967 0 2 2 VIRT UP UP 4 Access l26
16 1a020100 1 T 0 2 2 PHYS UP UP 4 Trunk
18 1a020300 1 T 0 2 2 PHYS UP UP 4 Trunk
pvlan promiscuous trunk port
19 1a020400 1 T 0 2 2 PHYS UP UP 4 Trunk
pvlan promiscuous trunk port
47 1b020000 154 0 2 0 VIRT UP UP 4 Access
If additional information is required for Cisco Technical Support to troubleshoot a private VLAN issue, use the following commands:
•show system internal private-vlan info
•show system internal private-vlan event-history traces