The document discusses Cisco's StackWise-480 technology used in the Cisco 3850 series switches. StackWise-480 allows switches to be stacked together and operate as a single, unified switch with up to 480 Gbps of bandwidth between stacked switches. It utilizes a ring topology with three eastbound and three westbound rings in each switch, providing high speed and fault tolerance. The stacking supports mixed models of Cisco 3850 switches with different port configurations.

1. Cisco 3850-Scalable StackWise-480
Scalable StackWise-480 on Cisco 3850 Series
We talked about the main Cisco Stacking switches before. The main Stacking
technology includes FlexStack, FlexStack Plus, StackWise, StackWise Plus,
StackWise-160, StackWise-480 and Virtual Switching System (VSS). In this
article, we will discuss the StackWise-480. What’s the StackWise-480?
The new StackWise-480 architecture builds high-speed, 480 Gbps per
stack switch member in the stack ring. This speed is much higher than the
traditional StackWise Plus design in the Catalyst 3750X Series platform.
The Stackwise 480 supports a centralized control-plane process, 1+1 state
full redundancy achieved by SSO, Distributed L2/L3 forwarding redundancy,
and utilizes the IOS HA framework.
The new Stackwise 480 cables are vastly different to the old clunk silver
battleships. The streamed lined cable pictured above replaces the old style.
Its makeup utilizes the concept of rings. There are three east bound and
three west bound rings. Each ring consists of 40 gigabit bandwidth. Amounts
to 240 gigabit through the stack. With reuse this number climbs to 480
gigabit. Packets traversing the stack-ring are segmented and reassembled in
hardware. This is done at 256 byte segments.
A fault in the stack is detected initially in hardware. This detection is passed
into the software. Once the software is notified the Ring Wrap process is
initiated. This process is sub millisecond. The process to heal is similar. The
switches on either side of the failure use their hardware first to detect the
other side. The software validates the link and the connection is reestablished
gracefully. This process is known as the Ring unwrap. It is important to note
that the unwrap is slower than the wrap.

2. Unicast packets on a Stackwise 480 support destination stripping. This means
that when a packet reaches its destination is removed from the ring. This
leaves the rest of the rings bandwidth free to be used. Multicast packets rely
on source stripping. Source stripping requires a packet that traverse the ring
upon arrival to the destination, copy the packet and send it the rest of the
way to the source and then is removed from the ring. This is wasteful and
bandwidth intensive.
Unicast packets on a stack work on a token based access scheme with six
different tokens associated to the six rings. Depending on the tokens which
each specific ASIC has access to they might use two or three, or consume all
six. Due to the nature of 3 east and 3 west links the ability to pass traffic
around half the ring is extremely effective. I like to remember the behavior of
Unicast packets on a stack as half-ring!

3. Multicast packets on a Stackwise 480 works with source stripping. When a
multicast packet comes in they are sent out to particular ASICs. It is sent out
around the ring and interested parties pick up the packet. It is continued
around the stack and back to the source where it is stripped and discarded.
This method allows stack members and their ASICs that might need the
multicast packet to be able to get it. Any node that does get the multicast
packet replicates it for the outbound and local ports. This saves on congestion
arising from sending individual copies.
The 3850 Stackwise 480 expands upon the new inbuilt ASICs to help
achieve up to 200 forwarding, non blocking ports. Stackwise 480 allows the
entire unit to stack up to 480 Gigabits of forwarding capacity. There is a limit
of 4 switches per stack and this is something to consider during a design. The
notion of an Master, hot-standby, and standby units allows the switch to be
highly resilient due to the ability to now leverage SSO technologies.
The ASIC aforementioned which is the beating heart of the Catalyst
3850 is known as the UADP ASIC. It supports programmability and
intelligence with foundation support for Cisco Open Network Environment,
Software Defined Unicorn support, and OnePK movements. This is expected
to be expanded via software updates.
Scalable StackWise-480 Architecture on Cisco 3850 Series Switches
Catalyst 3850 Series Switches are supported in three different form factor
models: 48 ports 10/100/1000, 24 ports 10/100/1000, and 12/24 Ethernet
small form-factor pluggable (SFP) ports. The hardware design of each model
is cost-effective to support different network capacity load and switching

4. performance. For consistent converged access capabilities with rich Unified
Access network services in the wiring closet, the software parity remains
common in Catalyst 3850 switch models.
The Cisco IOS XE 3.3 software release brings parity of the nine-members-
switch-stack capability that can be physically connected in a ring to form a
single, unified, virtual stack system. Depending on the port density
requirement in each stack switch, the Catalyst 3850 hardware provides
flexibility for mix-mode support between 48-, 24-, and 12-port systems in
single stack ring. The Catalyst 3850 deployed in stack mode is designed to
deliver deterministic and non-blocking switching performance for up to 468
ports, including wired and wireless network devices. The switching
performance delivers hardware-accelerated, integrated borderless network
services such Power over Ethernet (PoE) and PoE Plus, quality of service
(QoS), access control lists (ACLs), Flexible Netflow, and many more
services on every port.
StackWise-480 supports a mixed stack of any Catalyst 3850 models (48
ports 10/100/1000, 24 ports 10/100/1000, and 12/24 Ethernet SFP
ports). You can mix the switches with different number of access ports (48,
24, and 12), different type of access ports (copper and fiber, PoE, and non-
PoE-capable), and different network modules. But all switches in one stack
must have the same version of IOS XE and the same feature set license. A
mixed stack of LAN base switches with IP base or IP services is not supported.
Catalyst 3850 Series Switches with a LAN base feature set can only stack with
other Catalyst 3850 Series LAN base switches. The same applies to IP base
and IP services as well.
Cisco StackWise Architecture Comparison
Catalyst
3850
StackWise-
480
Catalyst
3650
StackWise-
160
Catalyst
3750-X
StackWise
Plus
Stack ports per switch 2 2 2
Ring per stack port 6 2 2
Throughput per ring (bi-
directional)
40 Gbps 40 Gbps 16 Gbps
Throughput per stack 240 Gbps 80 Gbps 32 Gbps

5. port/ASIC
Throughput per switch
(dual stack ports)
with SRP
480 Gbps 160 Gbps 64 Gbps
Cisco Catalyst 3850: Comparison with Catalyst 3750-X
Features Cisco Catalyst
3750-X
Cisco Catalyst 3850
Stacking bandwidth 64 Gbps 480 Gbps**
Cisco IOS Software
wireless controller
No Yes
Queues per port 4 8
Quality-of-service (QoS)
model
MLS MQC
Uplinks**** 4 x 1GE
2 x 10GE NM
4 x 1 GE or 2 x 10GE
SM
4 x 1GE
2 x 1/10GE
4 x 1/10GE*
8 x 10GE***
2 x 40GE***
Downlinks 24 or 48 RJ45
interfaces
12 or 24 SFP
receptacles
24 or 48 RJ45
interfaces
12 or 24 SFP
receptacles
12, 24, or 24 SFP+
receptacles

6. StackPower Yes Yes**
Flexible NetFlow support Yes (C3KX-SM-10G
required)
Yes
Multicore CPU for hosted
services
No Yes
Flash size 64 Mb 2 Gb
Operating system Cisco IOS Software Cisco IOS XE Software
*Available only for the 48-port RJ45 models and for the 12-port (or higher) 10
Gigabit capable models
**StackWise-480 and StackPower not supported on the 48-port 10G SFP+
switch
*** Supported on the 24-port and 48-port Multigigabit Switch and also on the
24-port 10G SFP+ switch
****Optional uplink modules are not supported on the 48-port 10G SFP+
switch
More Related Cisco Switch Stack Topics
All about Cisco’s Stacking Switches
Cisco Switch Stacking Using a Couple of Cisco Catalyst 3650
Cisco 2960-S Series Stacking
Stacking Cisco 3750 Switches Benefits & Stacking Rules
How to Stack Cisco 2960S Switches…Detailed Examples Here
Cisco Catalyst 3850 switch Stacking
Cisco Catalyst 2960-S & 2960-X Mixed Stacking