Describe chassis virtualization and aggregation technologies

Cisco stack wise technology has come with an interesting method for collectively using the abilities of a stack of switches. A 32 Gbps switching stack is interconnected to develop a single switching unit, with the joining of individual switches very cleverly. A single switching unit is created with the configuration and routing information being used by every switch in the stack. Without affecting the processing, switches can be added and deleted from a working stack. By creating a bi-directional closed loop path, a single logical unit can be created since all the switches unite as well. Full access to stack interconnect bandwidth is given to all stack members. A master switch is developed when a stack, managed in a single unit, is elected form one of the stack members switches.

Every switch in the stack has the ability to act as a master or subordinate member in the hierarchy. The master switch is selected and it behaves as the control center for the stack. The master member switches behave as the forwarding processors. Every switch has a number assigned to it. Nine separate switches can be grouped together. The stack performance will not be affected by the addition and deletion of switches. Every stack of the Cisco 3500 series switches has a single IP address and is handled as a single object. This single IP management, implements to activities such as, fault detection, virtual LAN (VLLAN) development and changes, security, and QoS controls. Every stack has its own configuration file which is given to every member in the stack. This lets every switch in the stack to use the same network topology, MAC address, and routing information. On the other hand, it lets any member to act as the master, if the master ever fails.

Stack wise switch

The stack inter connect functionality:

Cisco stack wise technology builds up into nine individual Cisco catalyst 3750 switches into a single logical unit; by utilizing special stack interconnect cables and stacking software. The stack acts a s a single switching unit that is handled by the master switch chosen from one of the member switches. The master switch develops and upgrades all the switching and optional routing tables. A stack in working can take in new members, or delete old ones without any service disruption.

Bi-directional Flow:

To perfectly load balance the traffic, packets are situated between two logical counter rotating paths. Every counter rotating path uses 16 Gpbs in both the directions, holding together traffic total of 32 Gbps bi-directionally. The egress queues configure path usage to help confirm that the traffic load is equally divided.

Whenever a frame is ready to be transferred onto a path, measurement is made to see which path has the most accessible bandwidth. A replica is made of the entire frame onto this half of the path. Traffic is worked upon depending upon its class of service or divided services code point designation (DSCP). Low traffic is always given more importance. If for instance, a breakage is tracked down in a cable, the traffic is automatically wrapped back across the single remaining 16 Gbps path to start forwarding further.

Online Stack Add's and removals:

Without disturbing the working performance, switches can be added and deleted to a working stack. Once a new switch is added, the master switch immediately configures the unit with the presently working Cisco IOS software image and configuration of the stack. The stack will collect information such as switching table information and updating the MAC tables as new addresses are taught. Before the switch is ready to function, the network manager has nothing to do with it. Without any effect on the rest of the switches, the switches can be removed from the stack in process. When the stack finds out that a series of ports is absent it will automatically update that information without affecting forwarding or routing.

Physical Sequential Linkage:

The switches are connected to each other very systematically and in sequence. Any break in any of their cables will obviously result in stack bandwidth being lessened to half of its complete capabilities. Sub-second timing mechanism a figure out traffic problems and automatically insists over failover. The mechanism keeps the dual path flow in record when the timing mechanisms find out any sort of new activity on the cable.

Single Management IP Address:

A single IP address is delivered to a stack as a part of the configuration done in the beginning. As soon as the stack IP address is developed, the physical switches connected to it become a part of the master switch group. Once it is connected to a group, every switch will utilize the stack IP address. Once a new master is selected, it uses this IP address to continue staying in touch with the network.

Stack Creation and Modification:

Stacks are developed when single switches are connected together with stacking cables. If the stack ports find out electromechanical activity, every port begins to send information regarding its switch. Once the entire set of switches is known, the stack selects one of the members to be the master switch for the rest, which will basically be given the task of configuring files and routing information and other stack data. The complete stack will have a single IP address which will be used by the entire switches.

1:N Master Redundancy:

1:N master redundancy lets each stack member to work as a master, giving the highest consistency for forwarding. Every switch in the stack can behave as a master, developing 1:N availability scheme for a network control. In the least happening event of a single unit failure, the other units still continue to forward traffic and keep up with their performance.

Master Switch Election:

The stack acts as a single switching unit which is handled by a master switch, which is selected by the member switches. The master switch immediately develops and upgrades all the switching and optional routing tables. Any member of the stack can actually be the master switch. On the installation, or restart of the entire stack, a process of election happens among the switches present in the stack. There is a certain kind of selection criteria developed for the selection of master switch.

Activities of Master switch

Master switch performs for the IP functions as primary contact point such as pings, telnet sessions, routing information and command line interface. The master switch downloads the forwarding tables to every subordinate switch. Unicast and Multicast routing functions are implemented through master switch. ACL and Qos configuration data information is broadcasted from the master switch to subordinates. After adding a new subordinate switch, or when the existing switch is removed, the master will switch will provide notification of this situation, updating the tables of each subordinate switch.

Shared Network Topology Information

Master switch is also accountable for maintaining and collecting the appropriate configuration and routing information. It keeps all this information recent by sending updates and copies periodically to every subordinate switch in stack. When a latest master switch is selected, it will reapply the configuration running from previous master switch to assist network continuity and user. It is important to know that the master switch will perform processing and routing control. Each switch in stack will perform the forwarding based on the data and information provided by master switch.

Activities of Subordinate Switch

Every subordinate switch consists of tables for saving its own MAC addresses and the other MAC addresses tables in stack. The master switch will keep MAC address tables reported to stack. The master switch also prepares a MAC addresses map for the entire stake and will distribute it to the subordinates. Every switch will become aware of each port in stack. This removes the repetitive learning process, creating a faster and efficient switching architecture for the network system.

The subordinate switches will maintain their personal spanning tree for every supported VLAN. The stackwise ports will never be forwarded in the spanning tree blocking state. Master switch will keep a copy of every table of spanning free for all VLAN in stack. Once a new VLAN is removed or added, the existing switches will obtain a notification of this case, updating the tables accordingly.

Subordinate switches tend to wait before receiving the copies of configurations in run from the master switch and start transmitting information to the receipt of the latest information. This feature assists in ensuring that all the ports will be using only the recent information and there will be only a single network topology in use for making forwarding decisions.

Layer 3 and Layer 2 Forwardin

The stackwise technology by Cisco offers a unique method for layer 3 and layer 2 management forwarding. Layer 2 forwarding is performed through a distributed method while the layer 3 is performed through a centralized method. This provides the best possible efficiency and resiliency for switching and routing functions across stack.

During the Master Change, Forwarding Resiliency

After a master switch is disabled or becomes inactive, and during the time new master switch is being elected, the stack will continue to perform its function. Layer 2 functions will perform, unaffected. New master switch utilizes unicast table that is hot standby to further proceed with unicast traffic. Routing tables and multicast tables are reloaded and flushed to prevent loops. NSF protects the layer 3 resiliency, which rapidly and gracefully transits layer 3 forwarding from old to fresh master mode.

New Members

After the switching stack establishes a master switch, a fresh switch is added automatically after a while and becomes a subordinate. All the present addressing and routing information is loaded in the subordinate as to allow it to immediately start transmitting traffic. The ports will become familiar with the IP address of switch. Global information like Qos configuration is downloaded in the new subordinate member.

Cisco IOS Software

The stackwise technology by cisco demands that every unit in stack should run similar Cisco IOS software release. After building the stack, it is suggested that entire stack members have same software functions set, either all IP service or IP base. This is due to the fact that later update of Cisco IOS software commands that all switches should be updated to the same version as that of master.

Upgrades in the Stack (Applicable to all devices)

As the switch stack acts like one unit, the updates apply universally to the entire member area of stack in one go. This implies that if single stack, which is the original one contains a combination of IP service and IP base , software functions sets on different switches, the first time Cisco IOS software update is implied, all the units in stack will take over the characteristics of the applied image. Although it becomes more efficient to add efficiency to stack, it should be noted that all upgrades that are applicable have been bought before allowing the units to be upgraded from IP services to IP base functions.

Smart Unicast and Multicast -

The Stackwise technology by cisco utilizes a highly efficient mechanism of multicast and unicast traffic transmitting. Every data packet is placed on stack interconnected once only. This consists of multicast packets. Every packet of data includes a 24-byte destination or header and how the packet should be used. In the situation of multicast, master switch will identify the port which should receive the copy of packets and will add a destination index for every port. A copy of packet is added on the stack interconnect. Every switch port which has one destination index will be able to copy this packet.


The products using Stack wise technologies can be handled by the network or CLI management packages. CMS, known as Cluster management suite has been designed particularly for Cisco stackable switch management. The special features of CMS software will allow the network manager configure the ports in stack with similar profile. Predefined wizards for information, video, voice, security, inter vlan routing and multicast features allow the network manager to establish all port configuration process at once.

Cross-Stack EtherChannel

As the ports in stack act like on single unit, the technology of etherchannel will operate across different devices in stack. The IOS software by cisco increases up to eight different physical ports from any of the switch in stack in single logical uplink.

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