Medianet Reference Guide - Cisco

Chapter 3
Medianet Availability Design Considerations
Device Availability Technologies
the way around the ring and returns to the source, it is stripped off the ring. This means bandwidth
is used up all the way around the ring, even if the packet is destined for a directly attached neighbor.
Destination stripping means that when the packet reaches its destination, it is removed from the ring
and continues no further. This leaves the rest of the ring bandwidth free to be used. Thus, the
throughput performance of the stack is multiplied to a minimum value of 64 Gbps bidirectionally.
This ability to free up bandwidth is sometimes referred to as spatial reuse.
Note
Even in StackWise Plus, broadcast and multicast packets must use source stripping because the
packet may have multiple targets on the stack.
• StackWise Plus can locally switch, whereas StackWise cannot. Furthermore, in StackWise, because
there is no local switching and there is source stripping, even locally destined packets must traverse
the entire stack ring.
• StackWise Plus supports up to two Ten Gigabit Ethernet ports per Cisco Catalyst 3750-E.
Finally, both StackWise and StackWise Plus can support Layer 3 non-stop forwarding (NSF) when two
or more nodes are present in a stack.
Non-Stop Forwarding with Stateful Switch Over
Stateful switchover (SSO) is a redundant route- and/or switch-processor availability feature that
significantly reduces MTTR by allowing extremely fast switching between the main and backup
processors. SSO is supported on routers (such as the Cisco 7600, 10000, and 12000 Series) and switches
(such as the Cisco Catalyst 4500 and 6500 Series).
Before discussing the details of SSO, a few definitions may be helpful. For example, state in SSO refers
to maintaining between the active and standby processors, among many other elements, the protocol
configurations and current status of the following:
• Layer 2 (L2)
• Layer 3 (L3)
• Multicast
• QoS policy
• Access list policy
• Interface
Also, the adjectives cold, warm, and hot are used to denote the readiness of the system and its
components to assume the network services functionality and the job of forwarding packets to their
destination. These terms appear in conjunction with Cisco IOS verification command output relating to
NSF/SSO, as well as with many high availability feature descriptions. These terms are generally defined
as follows:
• Cold—The minimum degree of resiliency that has been traditionally provided by a redundant
system. A redundant system is cold when no state information is maintained between the backup or
standby system and the system to which it offers protection. Typically, a cold system must complete
a boot process before it comes online and is ready to take over from a failed system.
• Warm—A degree of resiliency beyond the cold standby system. In this case, the redundant system
has been partially prepared, but does not have all the state information known by the primary system
to take over immediately. Additional information must be determined or gleaned from the traffic
flow or the peer network devices to handle packet forwarding. A warm system is already booted and
needs to learn or generate only the state information before taking over from a failed system.
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Medianet Reference Guide
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