Chapter 2) Implementing Data Center Switching Protocols Flashcards
Describe the function of Spanning Tree edge ports.
Edge ports in spanning tree connect directly to end hosts. These ports can be either an access port or trunk port, and immediately transition to the forwarding state.
Describe the function of Spanning Tree network ports.
Network ports are normally connected only to switches or bridges. Bridge assurance is enabled only on network ports.
Describe the function of Spanning tree normal ports.
Normal ports can be connected to either hosts, switches, or bridges. These ports function as normal spanning tree ports.
What is the default spanning tree port type?
The default spanning tree interface is a normal port.
What is the function of the STP Bridge Assurance extension?
Spanning tree Bridge Assurance is one of those features that help prevent bridging loops in Layer 2 networks. When a BPDU is not received on an interface for a certain period of time, the port is disabled until it receives BDPUs again.
What is the function of the STP BPDU Guard extension?
This extension disables ports that receive a BPDU frame; it is useful for edge ports that should never be connected to another switch.
What is the function of the STP BPDU Filtering extension?
This extension prevents the switch from sending or even receiving BPDUs on a specified edge port.
What is the function of the STP Loop Guard extension?
This extension protects against network interfaces that malfunction. Loop Guard is useful only in switched networks where devices are connected by point-to-point links.
What is the function of the STP Root Guard extension?
This extension prevents a port from becoming a root port or a blocked port.
What is the default mode of STP for Cisco Nexus Switches?
Rapid PVST+
When do designated and root ports generate a TC (Topology Change)?
When the interface fails to receive 3 consecutive BPDUs, or when the max age timer expires.
What is the role and value of the TC While timer?
The TC While timer is equivalent to the hello interval + 1 second. While the TC While timer is running, the interface continues to set the TC flag on all BPDUs sent on that port.
What are the 4 Rapid PVST+ and MST port states?
Blocking: The switch LAN port does not participate in frame forwarding.
Learning: The switch LAN port prepares to participate in frame forwarding.
Forwarding: The switch LAN port forwards frames.
Disabled: The switch LAN port does not participate in STP and does not forward frames.
What the SPT short & high path-costs for a 10 Mbps link?
Short Path: 100
Long Path: 2,000,000
What the SPT short & high path-costs for a 100 Mbps link?
Short Path: 19
Long Path: 200,000
What the SPT short & high path-costs for a 1 Gbps link?
Short Path: 4
Long Path: 20,000
What the SPT short & high path-costs for a 10 Gbps link?
Short Path: 2
Long Path: 2000
What is the default Rapid PVST+ port priority value?
Default is 128.
What is the range of Rapid PVST+ port priority values?
0 to 224, in increments of 32.
What is the only Rapid PVST+ extension that is enabled on Cisco NX-OS by default?
STP Bridge Assurance.
What are the maximum amount of interfaces that can be supported in a single port channel?
8 or 16, depending on the hardware and software support in Cisco NX-OS.
What are the types of port channels that are supported by Cisco NX-OS?
Static, or LACP (Link Aggregation Control Protocol).
PAgP (Port Aggregation Protocol) is not a supported mode in Cisco NX-OS.
What is the difference between A vPC (Virtual Port Channel) and a VSS link (Virtual Switch System)?
The key difference between a vPC and a VSS is that the VSS creates a single logical switch. This results in a single control plane for both management and configuration purposes. With vPCs, each Cisco Nexus switch (vPC) is managed and configured independently. A vPC allows the creation of Layer 2 port channels that span two switches.
Describe the function of a vPC peer-keepalive or fault-tolerant link.
A routed “link” (it is more accurate to say path) used to resolve dual-active scenarios in which the peer link connectivityis lost.
Describe the function of the vPC peer link.
This link is used to create the illusion of a single control plane by forwarding BPDUs or LACP packets to the primary vPC switch from the secondary vPC switch. It is also used to synchronize ARP and IGMP entries between both devices.
What type of priority is preferred in vPC primary and secondary elections? How are these roles affected by preemption?
The device with the lower number configured as its priority is preferred. Preemption is not available in vPC so device cannot automatically take back its role as the primary switch.
What happens to the roles of the primary and secondary vPC switches when the vPC peer link is disconnected?
As long as the vPC peer-keepalive (or fault-tolerant link) is still active, the vPC operational roles stay unchanged.
What happens to the roles of the primary and secondary vPC switches when the vPC peer link AND vPC peer-keepalive (or fault-tolerant link) are both disconnected.
Connectivity is lost between the primary and secondary switches, so both devices take the role as the primary switch.
Describe how BPDUs are forwarded between the primary and secondary switches in a vPC domain.
The vPC, by default, ensures that only the primary switch forwards BPDUs on vPCs. The BPDUs that may be received by the secondary vPC peer on a vPC port are forwarded to the primary vPC peer through the peer link for processing.
What is a Type-1 misconfiguration in regards to vPC?
A Type-1 inconsistency is a mismatch in configuration(s) between the primary and secondary switches that will cause all member ports in the channel to be suspended.
What is a Type-2 misconfiguration in regards to vPC?
A Type-1 inconsistency is a mismatch in configuration(s) between the primary and secondary switches that will warn the user, but will not suspend the port channel.
What are the 2 types of vPC configuration inconsistencies?
Inconsistencies can be global or interface specific:
- Global inconsistencies: Type-1 global inconsistencies affect all vPC member ports (but
do not affect non-vPC ports). - Interface-specific inconsistencies: Type-1 interface-specific inconsistencies affect
only the interface itself
What type of misconfiguration is a mismatch of MTU value on a port in a vPC connection?
Type 1: The port channel will be suspended.
What type of misconfiguration is a mismatch of Spanning tree global settings (Bridge Assurance, Loop Guard, and Root Guard)?
Type 1: The port channel will be suspended.
What type of misconfiguration is a mismatch of Multiple Spanning Tree (MST) region definition (VLAN-to-instance mapping) settings?
Type 1: The port channel will be suspended.
What type of misconfiguration is a mismatch of port channel modes, trunk modes, and spanning tree interface settings?
Type 1: The port channel will be suspended.
How does vPC ensure that duplicate frames are not present in the toplogy?
One of the most important forwarding rules for vPC is that a frame that enters the vPC peer
switch from the peer link cannot exit the switch from a vPC member port.
How does HSRP function when configured as the gateway in a vPC domain?
In normal Hot Standby Router Protocol operation, the active HSRP interface answers ARP requests, but with a vPC, both HSRP interfaces (active and standby) can forward traffic.
What protocol is used by vPC to synchronize ARP information between the primary and secondary switches after they are reconnected??
When two switches are reconnected after a failure, they use the Cisco Fabric Services protocol over Ethernet to perform bulk synchronization of the ARP table.
