Networking overview

The Network page in the IBM Storage Fusion user interface provides a view of the networking details in your appliance. You can view information about switches, VLANs, and links.

Basic concepts

A virtual LAN (VLAN) is an isolated broadcast domain that is created within a switch. Each VLAN created within a switch is isolated from other VLANs. The network traffic can pass from one VLAN to another by adding a routing device. The routing functions must be provided at the data center core network.
A Multi-Chassis Link Aggregation Group (MLAG) allows for multi-system link aggregation and facilitates active-active uplinks of access layer switches. An MLAG with no Spanning Tree configured avoids the wasted bandwidth that is associated with links that are blocked by the spanning tree.
To ensure high availability for the system, IBM Storage Fusion requires MLAG and link aggregation for the switches.
Switch LAG ID
This Switch LAG ID is used by high-speed switches inside the IBM Storage Fusion rack, which is not related to the LACP ID on (external) switch. It is unique for each IBM Storage Fusion rack and can be less than 250.

The high-speed switch (MLAG PAIR) that gets connected to customer switch must have a unique system MAC address (MLAG ID). This MLAG ID is used as source MAC address for traffic that is sourced from MLAG PAIR, such as STP BPDUs. The MLAG ID is internally derived from the Switch LAG ID. The specific Switch LAG ID is used as the last octet for "44:38:39:ff:00:xx".

Layer 2 connections
The connections from all the IBM Storage Fusion high-speed switches to the data center core network and customer management network are all layer 2 connections. IBM Storage Fusion supports the Link Aggregate Control Protocol (LACP) type of layer 2 aggregation.
The following characteristics describe layer 2 connections:
  • Layer 2 is considered switching and is done at the hardware layer.
  • Layer 2 is in the same broadcast domain or local network.
  • Layer 2 finds adjacent partners by MAC address.
Layer 3 connections
IBM Storage Fusion does not participate in any layer 3 routing or firewall functions. These functions are done in the data center core network.
The following characteristics describe layer 3 connections:
  • Layer 3 is considered routing and is done at the software layer.
  • Layer 3 knows how to traverse multiple networks (hops).
  • Layer 3 finds adjacent partners by IP address.
Spanning tree
In the networking stages of the installation for IBM Storage Fusion, an option to enable or disable the Spanning Tree is available. When you enable it, the spanning tree is enabled on the high-speed switches. By default, the option is disabled on these switches.
The high-speed switches in the IBM Storage Fusion rack support only rapid spanning-tree (RSTP) modes. It is also compatible with PVST and PVST+. Customer data networks that are running older spanning-tree methods (MST) are not supported.
Note: IBM Storage Fusion sets the spanning-tree bridge priority to 32768 as the default value. To avoid IBM Storage Fusion high-speed switches from becoming the spanning-tree root, the customer switch must have priority less than 32768. For more information, see Spanning Tree and Rapid Spanning Tree - STP.

Aggregation methods

IBM Storage Fusion supports the following aggregation methods for the connections on the customer data network:
The standard-based negotiation protocol, which is known as IEEE 802.1ax Link Aggregation Control Protocol (LACP), is a way to dynamically build an Etherchannel. The "active" end of the LACP group sends out special frames, which advertise the ability to form an Etherchannel. Typically, both ends are set to an "active" state. After these frames are exchanged, and if the ports on both sides agree that they support the requirements, LACP forms an Etherchannel. LACP is implemented in the switch by way of Linux bonding. Linux bonding provides a method for aggregating multiple network interfaces (members) into a single logical bonded interface (bond). Link aggregation is useful for linear scaling of bandwidth, load balancing, and failover protection.
No aggregation
If aggregation is not possible, this method is available, but not suggested, to provide high availability with no aggregation. With this method, it is suggested to enable Spanning Tree to avoid loops. When this method is used and Spanning Tree is enabled, one of the links is deactivated by STP, while the other link is enabled. This method is also called Aggregation None.
Note: LACP is the preferred choice. Use the no aggregation topology only if LACP is not possible as it does not provide the redundancy most clients require.

Port types

An access port provides access to a single VLAN only. Typically, the packets on an access port are raw Ethernet frames (untagged packets).
A trunk connection is used to pass traffic from multiple VLANs between two switches. All trunks use the IEEE 802.1Q standard. This link can be a single wire or one of the aggregations methods.

Supported topologies

To review examples of topologies that support high availability, see Network planning.