Upstream disjoint layer-2 networks (disjoint L2 networks) are required if you have two or more Ethernet “clouds” that never connect, but must be accessed by servers or virtual machines located in the same Cisco UCS domain. For example, you could configure disjoint L2 networks if you require one of the following:
Servers or virtual machines to access a public network and a backup network
In a multi-tenant system, servers or virtual machines for more than one customer are located in the same Cisco UCS domain and need to access the L2 networks for both customers.
By default, data traffic in Cisco UCS works on a principle of mutual inclusion. All traffic for all VLANs and upstream networks travels along all uplink ports and port channels. If you have upgraded from a release that does not support upstream disjoint layer-2 networks, you must assign the appropriate uplink interfaces to your VLANs, or traffic for those VLANs continues to flow along all uplink ports and port channels.
The configuration for disjoint L2 networks works on a principle of selective exclusion. Traffic for a VLAN that is designated as part of a disjoint network can only travel along an uplink Ethernet port or port channel that is specifically assigned to that VLAN, and is selectively excluded from all other uplink ports and port channels. However, traffic for VLANs that are not specifically assigned to an uplink Ethernet port or port channel can still travel on all uplink ports or port channels, including those that carry traffic for the disjoint L2 networks.
In Cisco UCS, the VLAN represents the upstream disjoint L2 network. When you design your network topology for disjoint L2 networks, you must assign uplink interfaces to VLANs not the reverse.
Guidelines for Configuring Upstream Disjoint L2 Networks
When you plan your configuration for upstream disjoint L2 networks, consider the following:
Ethernet Switching Mode Must Be End-Host Mode
Cisco UCS only supports disjoint L2 networks when the Ethernet switching mode of the fabric interconnects is configured for end-host mode. You cannot connect to disjoint L2 networks if the Ethernet switching mode of the fabric interconnects is switch mode.
Symmetrical Configuration Is Recommended for High Availability
If a Cisco UCS domain is configured for high availability with two fabric interconnects, we recommend that both fabric interconnects are configured with the same set of VLANs.
VLAN Validity Criteria Are the Same for Uplink Ethernet Ports and Port Channels
The VLAN used for the disjoint L2 networks must be configured and assigned to an uplink Ethernet port or uplink Ethernet port channel. If the port or port channel does not include the VLAN, Cisco UCS Manager considers the VLAN invalid and does the following:
Displays a configuration warning in the Status Details area for the server.
Ignores the configuration for the port or port channel and drops all traffic for that VLAN.
The validity criteria are the same for uplink Ethernet ports and uplink Ethernet port channels. Cisco UCS Manager does not differentiate between the two.
Overlapping VLANs Are Not Supported
Cisco UCS does not support overlapping VLANs in disjoint L2 networks. You must ensure that each VLAN only connects to one upstream disjoint L2 domain.
Each vNIC Can Only Communicate with One Disjoint L2 Network
A vNIC can only communicate with one disjoint L2 network. If a server needs to communicate with multiple disjoint L2 networks, you must configure a vNIC for each of those networks.
To communicate with more than two disjoint L2 networks, a server must have a Cisco VIC adapter that supports more than two vNICs.
Appliance Port Must Be Configured with the Same VLAN as Uplink Ethernet Port or Port Channel
For an appliance port to communicate with a disjoint L2 network, you must ensure that at least one uplink Ethernet port or port channel is in the same network and is therefore assigned to the same VLANs that are used by the appliance port. If Cisco UCS Manager cannot identify an uplink Ethernet port or port channel that includes all VLANs that carry traffic for an appliance port, the appliance port experiences a pinning failure and goes down.
For example, a Cisco UCS domain includes a global VLAN named vlan500 with an ID of 500. vlan500 is created as a global VLAN on the uplink Ethernet port. However, Cisco UCS Manager does not propagate this VLAN to appliance ports. To configure an appliance port with vlan500, you must create another VLAN named vlan500 with an ID of 500 for the appliance port. You can create this duplicate VLAN in the Appliances node on the LAN tab of the Cisco UCS Manager GUI or the eth-storage scope in the Cisco UCS Manager CLI. If you are prompted to check for VLAN Overlap, accept the overlap and Cisco UCS Manager creates the duplicate VLAN for the appliance port.
Default VLAN 1 Cannot Be Configured Explicitly on an Uplink Ethernet Port or Port Channel
Cisco UCS Manager implicitly assigns default VLAN 1 to all uplink ports and port channels. Even if you do not configure any other VLANs, Cisco UCS uses default VLAN 1 to handle data traffic for all uplink ports and port channels.
After you configure VLANs in a Cisco UCS domain, default VLAN 1 remains implicitly on all uplink ports and port channels. You cannot explicitly assign default VLAN 1 to an uplink port or port channel, nor can you remove it from an uplink port or port channel.
If you attempt to assign default VLAN 1 to a specific port or port channel, Cisco UCS Manager raises an Update Failed fault.
Therefore, if you configure a Cisco UCS domain for disjoint L2 networks, do not configure any vNICs with default VLAN 1 unless you want all data traffic for that server to be carried on all uplink Ethernet ports and port channels and sent to all upstream networks.
Pinning Considerations for Upstream Disjoint L2 Networks
Communication with an upstream disjoint L2 network requires that you ensure that the pinning is properly configured. Whether you implement soft pinning or hard pinning, a VLAN membership mismatch causes traffic for one or more VLANs to be dropped.
Soft pinning is the default behavior in Cisco UCS. If you plan to implement soft pinning, you do not need to create LAN pin groups to specify a pin target for a vNIC. Instead, Cisco UCS Manager pins the vNIC to an uplink Ethernet port or port channel according to VLAN membership criteria.
With soft pinning, Cisco UCS Manager validates data traffic from a vNIC against the VLAN membership of all uplink Ethernet ports and port channels. If you have configured disjoint L2 networks, Cisco UCS Manager must be able to find an uplink Ethernet port or port channel that is assigned to all VLANS on the vNIC. If no uplink Ethernet port or port channel is configured with all VLANs on the vNIC, Cisco UCS Manager does the following:
Brings the link down.
Drops the traffic for all of the VLANs on the vNIC.
Raises the following faults:
Cisco UCS Manager does not raise a fault or warning about the VLAN configuration.
For example, a vNIC on a server is configured with VLANs 101, 102, and 103. Interface 1/3 is assigned only to VLAN 102. Interfaces 1/1 and 1/2 are not explicitly assigned to a VLAN, which makes them available for traffic on VLANs 101 and 103. As a result of this configuration, the Cisco UCS domain does not include a border port interface that can carry traffic for all three VLANS for which the vNIC is configured. As a result, Cisco UCS Manager brings down the vNIC, drops traffic for all three VLANs on the vNIC, and raises the Link Down and VIF Down faults.
Hard pinning occurs when you use LAN pin groups to specify the pinning target for the traffic intended for the disjoint L2 networks. In turn, the uplink Ethernet port or port channel that is the pinning target must be configured to communicate with the appropriate disjoint L2 network.
With hard pinning, Cisco UCS Manager validates data traffic from a vNIC against the VLAN membership of all uplink Ethernet ports and port channels, and validates the LAN pin group configuration to ensure it includes the VLAN and the uplink Ethernet port or port channel. If the validation fails at any point, Cisco UCS Manager does the following:
Raises a Pinning VLAN Mismatch fault with a severity of Warning.
Drops traffic for the VLAN.
Does not bring the link down, so that traffic for other VLANs can continue to flow along it.
For example, if you want to configure hard pinning for an upstream disjoint L2 network that uses VLAN 177, do the following:
Create a LAN pin group with the uplink Ethernet port or port channel that carries the traffic for the disjoint L2 network.
Configure at least one vNIC in the service profile with VLAN 177 and the LAN pin group.
Assign VLAN 177 to an uplink Ethernet port or port channel included in the LAN pin group
If the configuration fails at any of these three points, then Cisco UCS Manager warns for a VLAN mismatch for VLAN 177 and drops the traffic for that VLAN only.
Configuring Cisco UCS for Upstream Disjoint L2 Networks
When you configure a Cisco UCS domain to connect with upstream disjoint L2 networks, you need to ensure that you complete all of the following steps.
Before You Begin
Before you begin this configuration, ensure that the ports on the fabric interconnects are properly cabled to support your disjoint L2 networks configuration.
Command or Action
Configure Ethernet switching mode for both fabric interconnects in Ethernet End-Host Mode.
The Ethernet switching mode must be in End-Host Mode for Cisco UCS to be able to communicate with upstream disjoint L2 networks.
Ensure that the service profiles for all servers that need to communicate with the disjoint L2 networks include the correct LAN connectivity configuration to ensure the vNICs send the traffic to the appropriate VLAN.
You can complete this configuration through one or more vNIC templates or when you configure the networking options for the service profile.
Deletes the specified Uplink Ethernet port channel assignment from the VLAN.
UCS-A /eth-uplink/vlan # commit-buffer
Commits the transaction to the system configuration.
If you remove all port or port channel interfaces from a VLAN, the VLAN returns to the default behavior and data traffic on that VLAN flows on all uplink ports and port channels. Depending upon the configuration in the Cisco UCS domain, this default behavior can cause Cisco UCS Manager to drop traffic for that VLAN. To avoid this occurrence, we recommend that you either assign at least one interface to the VLAN or delete the VLAN.
The following example deletes the association between uplink Ethernet port 2 on fabric interconnect A and the named VLAN called MyVLAN and commits the transaction: