4 - RSTP and EtherChannel Configuration Flashcards
What does the term access switch to refer to?
Switches that connect to endpoint devices
What does the term distribution switch refer to?
Switches that do NOT connect to end points, but connect to each access switch
What is PVST+?
Cisco proprietary Per VLAN STP protocol that creates one STP instance per VLAN
What is RPVST+?
Cisco proprietary Per VLAN RSTP protocol, including more features than the standardized RSTP
What is the IEEE equivalent of Cisco’s PVST+ / RPVST+?
Multiple Spanning Tree Protocol (MSTP)
True/False: Cisco Switches support standard STP/RSTP and PVST+ and RPVST+
False. They do not support single tree (CST)
What is the config parameter for PVST+?
pvst
What is the config parameter for RPVST+?
rapid-pvst
What is the config parameter for MSTP?
mst
What is the difference between the BID and priority field in normal STP/RSTP compared with PVST+/RPVST+?
The original priority field of 2 bytes is now divided into 4 bits of priority and a 12 bit subfield (System ID extension) aka VLAN ID
What values are valid for the PVST+/RPVST+ 4 bit priority field?
Still 0-65535 but in multiples of 4096
What’s another way to conveniently configure a switch priority for a given VLAN without setting a value manually?
spanning-tree vlan 2 root primary
OR
spanning-tree vlan 2 root secondary
How does RSTP differ from RPVST+ with regards to transmission of BPDUs?
RPVST+ sends one set of messages for each VLAN, opposed to one set of messages overall
What does RSTP do differently from RPVST+ with regards to transmission of messages on VLAN trunk links?
RSTP sends messages in native VLAN with no header/tag. RPVST+ sends each VLANs messages inside that VLAN with the 802.1Q header listing that VLAN
What is the TLV and what is it used for?
Type Length Value. RPVST+ adds to the BPDU that identifies the VLAN ID.
Standard RSTP doesn’t do this because it ignores VLANs
How do you set the switch priority for a given VLAN?
spanning-tree vlan 1 priority 4096
How do you configure a switch’s STP/RSTP port cost for a given port?
Interface subcommand:
spanning-tree vlan 1 cost x
What configuration command is used to configure EtherChannels on each physical interface?
channel-group
What is the difference between an EtherChannel and a PortChannel?
Nothing. They are the same thing
What is the difference between an EtherChannel and a Channel-group?
Nothing. They are the same thing
What command is used to show the status of an EtherChannel/Channel-group/Port Channel?
show etherchannel
What commands would you use to manually configure an EtherChannel?
int f0/1
channel-group 10 mode on
int f0/2
channel-group 10 mode on
How do you show a summary of a given EtherChannel?
show etherchannel 1 summary
How do Dynamic EtherChannel configuration protocols work?
Switches can use the protocol for particular channel-group number to exchange messages with neighboring switch to discover if configuration settings pass all checks. If so link is added to the EtherChannel and used.
What are two common protocols for dynamic EtherChannel configuration?
PAgP(Port Aggregation Protocol) - Cisco
LACP (Link Aggregation Control Protocol) - IEEE
How many EtherChannel links does LACP support?
16
How many EtherChannel links does PAgP support?
8
What two mode keywords are used when enabling PAgP?
desirable and auto
What two mode keywords are used when enabling LACP?
active and passive
Can you use the on keyword to configure LACP or PAgP?
No. This uses neither of those protocols
How would you configure PAgP on two switches?
SW1: channel-group 1 mode desirable
SW2: channel-group 1 mode auto | desirable
How would you configure LACP on two switches?
SW1: channel-group 1 mode active
SW2: channel-group 1 mode active | passive
What command would you use to verify an EtherChannel configuration?
show etherchannel 1 port-channel
What items must match on ALL ports participating in an EtherChannel?
- speed
- duplex
- operational access mode (ALL trunk or ALL access)
- access VLAN
- OR allowed VLAN list
- OR native VLAN
- STP interface settings
How do switches negotiate and check settings for EtherChannel between themselves and other switches?
Either use PAgP / LACP if already in use or CDP if using manual configuration
What would happen in an EtherChannel with mismatched STP cost?
It would fail
What command is used to configure EtherChannel load distribution?
Global command: port-channel load-balance
What values does EtherChannel load distribution use to make choices?
Various numeric values found in Layer 2, 3, and 4 headers
What are some common goals of using different EtherChannel load distribution methods?
- Cause all messages in single app flow to use the same link in a channel (prevent inadvertent reordering)
- Use all active links in EtherChannel adjusting to addition and removal of active links over time
- Balance traffic across active links
What command is used to show EtherChannel load balancing configuration?
show etherchannel load-balance
How would you show how a switch would distribute traffic on an EtherChannel?
test etherchannel load-balance interface po1 mac …
What standard is 802.w?
RSTP
What IEEE standard is 802.1D?
STP
What IEEE standard is MST?
802.1s
