Recently I needed to renew my Cisco CCNPs, that is both CCNP Routing and Switching as well as CCNP Security. While working with Cisco products (well now they own SourceFire, so exclude these) is not within my daily duties, I still thought it was important for me to maintain these two credentials. As a result, I've put together my notes below focusing on the key points I used to study. I believe that someone else may find them useful.
- Up to 9 switches can be stack together
- Uses the stackwise cable
- Make multiple physical switch into one logical switch
- If one cable is removed the loop will be broken but the stack will continue to works
- One switch in the stack becomes the "Master" and does all management tasks
- All switches other than the "Master" are "Members"
- Election process starts at installation or reboot of the entire stack
- Election process used:
"User Priority" Defined by user -> "Hardware/Software Priority" Switch with most extensive services get higher priority -> "Default configuration". Switch with configuration wins out switch with default configuration -> "Longest Uptime" -> "Lowest Mac Address"
- User priority is typically used to configure a master
- All switches share the same management IP, hostname, configuration, routing, topology, etc
- VSS (4500/6500) is the same as stackwise (3750)
- Stack is managed by the "Master" unit
- Both "Master" and "Member" switches act as forwarders
- Single IP used for management applies to: fault detection, virtual LAN (VLAN) creation and modification, security, and QoS controls
- Each stack has one only one configuration file which is distributed to each member of the stack
- Any member can become a master if the master fails
- Up to 9 3750 switches in a single unit
- Traffic flows in 16G per direction for a total of 32 GBPs across the stack
- When a new switch is added, the "Master" switch automatically configures the unit with the IOS image and the configuration of the stack
- The network manager does not need to do anything to bring up the switch
- Switches can be removed without any operational effect
- A break in any one of the cable will result in the bandwidth being reduced to half
- Uses subsecond
1:N master redundancy allows each stack member to serve as master
- 1:N If one switch fails all other units can continue to forward traffic
- When a new master is selected, it applies the configuration from the previous master
- master switch keeps a table of all the mac-addresses
- Master switch creates a map of all mac-address in the entire stack and distribute it to the subordinates
- each switch then becomes aware of every port in the stack
- subordinate switches keep their own spanning tree for each vlan they support
- Stackwise ring ports are never put into Spanning Tree protocol blocking state
- Master switch keeps a copy of all the spanning tree tables for each vlan in the stack
- Multiple switches in a stack can create an etherchannel
- Loss of connectivity in an individual switch will not effect the connectivity for other switches
- Switches can support dual homing to different routers for redundancy
- RPR+ for layer 3 resiliency: Each switch is initialized for routing capability and is ready to be elected as master if the master fails
- Layer 3 Nonstop Forwarding (NSF) is also supported in stacks of 2 or more
- Layer 2 is done in distributed method
- Layer 3 is done via centralized manner
- All units in the stack must use the same Cisco IOS software
- Recommended that the stack has the same feature set on each unit. However, not mandatory
- Later versions require that all switches be at the same version as the master
- If switch versions are not the same, one of 3 things happen.
1. If the hardware is supported, the master will download the IOS version it has in flash memory to the new switch, send the configur and bring the device online
2. If the hardware is supported and TFTP has been configured the Master will download and configure the new device
3. If hardware not supported, the new switch will be in suspended mode, noify the user of version incompatability and wait until the master is upgraded to an IOS version that support both types of hardware. Master then upgrades the rest of the stack, including the new switch
- Upgrade applies to all devices in the stack
- If there are different supported images in use, after the upgrade all members of the stack will have the same software
- Each data packet is put on the stack only once
- Each data packet has a 24 byte header
- Etherchannel technology can operate across multiple devices in the stack
- Etherchannel can aggregate up to 8 ports from any switches in the stack
- Up to 48 Etherchannel groups are supported on a stack
- Stackwise plus support destination stripping
- Stackwise supports source stripping
- highest priority number in the stack wins
- Lowest Mac Address wins
- Stack members cannot have the same number
- Cisco recommends specifying the stack master through the highest priority value
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