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# About logical interconnects

A logical interconnect is a single administrative entity that consists of the configuration for a set of interconnects in a single enclosure, and includes:

- The uplink sets, which connect to data center networks.

- The mapping of networks to physical uplink ports, which is defined by the uplink sets for a logical interconnect.

- The internal networks, which are used for server-to-server communications without traffic egressing any uplinks.

- The downlink ports, which connect through the enclosure midplane to the servers in the enclosure.

- The connections between interconnects, which are called stacking links. Stacking links can be internal cables (through the enclosure) or external cables between the external ports of interconnects.

See the appropriate support or compatibility matrix on the Hewlett Packard Enterprise Information Library for the maximum number of networks that can be provisioned on a logical interconnect.

For a server administrator, a logical interconnect represents the available networks through the interconnect uplinks and the interconnect downlink capabilities through a physical server’s interfaces. For a network administrator, a logical interconnect represents an Ethernet stacking configuration, aggregation layer connectivity, stacking topology, network reachability, statistics, and troubleshooting tools.

## About uplink sets

An uplink set defines a single, dedicated network or a group of networks and physical ports on a set of interconnects in an enclosure. An uplink set enables you to attach the interconnects to the data center networks. An uplink set enables multiple ports to support port aggregation (multiple ports connected to a single external interconnect) and link failover with a consistent set of VLAN networks.

- For tagged Ethernet networks, an uplink set enables you to identify interconnect uplinks that carry multiple networks over the same cable.

- For untagged or tunnel Ethernet networks, an uplink set identifies interconnect uplinks that are dedicated to a single network.

- For Fibre Channel networks, you can add one network to an uplink set. Fibre Channel does not allow virtual networks or VLANs.

- For Fibre Channel over Ethernet (FCoE) networks, an uplink set enables you to carry multiple Fibre Channel and tagged Ethernet networks over the same set of Ethernet cables.

- One uplink set per Cisco FEX module is allowed.

An uplink set is part of a logical interconnect. The initial configuration of the uplink sets for a logical interconnect is determined by the configuration of the uplink sets for the logical interconnect group, but you can change (override) the uplink sets for a specific logical interconnect.

Changes you make to the uplink sets for a logical interconnect group are not automatically propagated to existing logical interconnects. For example, to propagate a newly added VLAN to a logical interconnect group uplink set to its existing logical interconnects, you must individually update each logical interconnect configuration from the logical interconnect group.

For each logical interconnect:

- You can define zero or more uplink sets. See networking limits in the HPE OneView Support Matrix for the maximum number of supported uplink sets and the maximum network types supported in an uplink set.

  If you do not define any uplink sets, the servers in the enclosure cannot connect to data center networks.

- A network can be a member of one uplink set per logical interconnect group only.

- An uplink set with Fibre Channel or FCoE networks can use uplinks from only one interconnect.

- An uplink set can contain one or more tagged Ethernet networks. An uplink set for an untagged or a tunnel network can only contain that one untagged or tunnel network.

- An uplink set can contain one or more FCoE networks, but the uplinks must be contained within a single FCoE-capable interconnect.

  See firmware requirements in About Fibre Channel over Ethernet (FCoE) networks.

- Within a logical interconnect group or logical interconnect, all VLAN IDs must be unique across uplink sets and internal networks.

- Internal networks allow server-to-server connectivity within the logical interconnect. Internal networks are created by adding existing networks to the internal networks set. Internal networks can be added to uplink sets which automatically removes them from the internal networks set.

  Cisco FEX modules do not support internal networks.

- Ethernet networks in an uplink set must be specified individually and cannot be specified by selecting a network set. The use of network sets in uplink sets is not supported for the following reasons:

  - The networking configuration is intended to be managed by users with a role of Network administrator. Because users with a role of Server administrator can create and edit network sets, allowing network sets to be members of uplink sets could result in server administrators changing the mapping of networks to uplink ports without the knowledge of the network administrator.

  - Because a network can be a member of more than one network set, allowing network sets to be members of uplink sets would make it more difficult to ensure that no single network is a member of more than one uplink set, especially as the network set configurations change over time.

## About internal networks

An internal network is a network that has no uplink ports and is used for server-to-server communications within a logical interconnect. Servers that communicate with each other over internal networks do so without the traffic egressing any uplinks.

Only tagged, untagged, and tunnel Ethernet networks can be members of internal networks.

If network connectivity outside of the logical enclosure is required, the network must be in an uplink set associated with an uplink.

| NOTE: A network is not available for profile connections until it is added to an uplink set or internal networks in a logical interconnect group and the associated logical interconnect.

#### Adding and removing internal networks

Each logical interconnect group and logical interconnect has an internal network list which is initially empty. Adding a network to the internal network list in both the logical interconnect group and logical interconnect allows it to be used in server profile connections that can be mapped to downlinks on the interconnects within the logical interconnect.

| IMPORTANT: Duplicate networks in the internal networks list on more than one logical interconnect can result in the inability for the servers in the enclosure to communicate. Therefore, it is recommended to define all your internal networks on one logical interconnect in the enclosure.

You can add or remove internal networks from the Logical Interconnects or Logical Interconnect Groups screen. The internal network configuration created in the logical interconnect group is inherited by associated logical interconnects. A logical interconnect can be made consistent with the parent logical interconnect group by selecting Actions→Update from group.

Networks in the internal networks list appear as available networks for uplink sets. They are automatically removed from internal networks if they are added to an uplink set.

Removing an Ethernet network from an uplink set in a logical interconnect automatically moves it to internal networks so network connectivity is not lost for server profile connections using the network. However, if you remove an Ethernet network from an uplink set in a logical interconnect group, the network does not get moved automatically to the internal networks. If you want the network to be internal, edit the logical interconnect group and add the network to the internal networks.

## About stacking links and stacking health

#### Stacking links

Stacking links apply to Ethernet networks only. You can connect all the interconnects to one another through stacking links so that Ethernet traffic from a server connected to an interconnect downlink can reach the data center networks through that interconnect or through a stacking link from that interconnect to another interconnect. When adding enclosures, create a single logical interconnect group with a single logical interconnect that contains all interconnects within the enclosure. This creates a fully stacked enclosure.

To set up an enclosure that is not stacked, configure multiple logical interconnect groups where each interconnect is in a separate logical interconnect group (and subsequently separate logical interconnects) before adding the enclosure. You can also set up a partially-stacked enclosure where you have more than one interconnect in a logical interconnect group. See About multiple logical interconnect groups in an enclosure group for more information.

#### Stacking health

The appliance detects the topology within an enclosure of the connections between interconnects, and determines the redundancy of paths between servers and data center networks. The appliance reports redundancy information as the stacking health of the logical interconnect, which is one of the following:

`Redundantly Connected` | There are at least two independent paths between any pair of interconnects in the logical interconnect, and there are at least two independent paths from any downlink port on any interconnect in the logical interconnect to any other port (uplink or downlink) in the logical interconnect.
`Connected` | There is a single path between any pair of interconnects in the logical interconnect, and there is a single path from any downlink port on any interconnect in the logical interconnect to any other port (uplink or downlink) in the logical interconnect.
`Disconnected` | At least one interconnect is not connected to the other member interconnects in the logical interconnect.
`Not applicable` | Interconnects do not support stacking or there is a single interconnect in the logical interconnect.

## Creating or deleting a logical interconnect

#### Creating a logical interconnect in an enclosure

A logical interconnect is automatically added when the enclosure is added. When you add a c7000 enclosure, the following occurs:

- A logical enclosure is created based on the defined enclosure group

- The appliance detects the physical interconnects and their stacking links, if any.

- The appliance automatically creates a single logical interconnect for each logical interconnect group defined in the enclosure group.

  | NOTE: The number of logical interconnects that are created depends on how the enclosure group was defined. See Update a logical interconnect group

- The appliance automatically names the logical interconnects using the following naming convention:

  ``logical_enclosure_name`-`logical_interconnect_group_name``

- The data for the logical interconnects displays on the Logical Interconnects screen.

To add or change logical interconnects, see Edit a logical interconnect group in the online help Update a logical interconnect group for more information.

#### Deleting a logical interconnect

To delete a logical interconnect, you must remove the logical interconnect group from the enclosure group, and then perform an update from group on the logical enclosure. This deletes the logical interconnect from the logical enclosure.

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