CCNP switch slides 3 Flashcards
source
http://quizlet.com/3373148/ccnp-switch-deck-3-flash-cards/
what are the 5 STP port roles?
root, designated, blocking, alternate, forwarding (host)
what does Root Guard do?
controls where candidate root bridges can be connected and found on a network
How does Root Guard work?
a port can only forward or relay BPDUs, but can’t receive them, disabled by default, enabled per-port, blocks port when superior BPDUs are received
How is Root Guard used?
on ports where you never expect to find a root bridge for a VLAN
What is BPDU Guard?
if any BPDU is received on a port, it puts the port into the errdisable state
How can BPDU Guard be configured?
globally or per-port
What does Loop Guard do?
tracks BPDUs on nondesignated ports. When those BPDUs stop coming, the port is put into loop-inconsistent state and blocks
How does loop guard block ports?
only for the offending VLAN on the port
What does UDLD do?
protects STP when a physical malfunction only allows traffic in 1 direction, even though the link shows as up (cisco proprietary)
How does UDLD work?
sends special layer 2 UDLD frames and expects an echo. Both ends must be configured for UDLD
How should UDLD be configured?
the configureable UDLD interval must be less than max age plus two intervals of forward delay
What are the 2 UDLD modes?
normal and aggressive
What is UDLD normal mode?
if a unidirectional link is detected, the port continues normally, but the port is marked as undetermined and a syslog is generated
What is UDLD aggressive mode?
If a unidirectional link is detected, the switch doesn’t try to reestablish the link. ULD msgs are sent once/sec for 8 seconds, then the port is err-disabled
How is UDLD configured?
per-port or globally for all fiber-optic ports. Can be enabled globally, but will only affect fiber ports
What does BPDU filtering do?
effectively stops STP on filtered ports
Where is root guard enabled?
all ports where root isn’t expected
where is BPDU guard enabled?
all user ports that have portfast enabled
where is loop guard enabled?
all nondesignated ports, but ok for all ports
where is UDLD enabled?
all fiber-optic links between switches (must be enabled on both ends)
Can loop guard and udld be used together?
yes
can root guard and udld be used together?
yes
can root guard and loop guard be used together
no
can root guard and BPDU guard be used together?
no
should BPDU guard and BPDU filter be used together?
no
RSTP uses which standard?
802.1w
What are the RSTP port roles?
root, designated, alternate, and backup
RSTP root port
port with best root path cost
RSTP designated port
Port with best root path cost on segment
RSTP alternate port
port with alternative path to root less desirable than root
RSTP backup port
port with redundant, but less deisrable connection to a segment. Possibly root candidate
What are the RSTP port states?
discarding, learning, forwarding
RSTP discarding state
incoming frames are dropped (combination of disabled, blocking, and listening)
RSTP learning state
incoming frames dropped, but MACs learned
RSTP forwarding state
frames are forwarded
RSTP BPDU structure
some unused bits are used to allow a port to identify its role and state. Also the BPDUs state that they are V2 BPDUs
When are RSTP BPDUs sent?
every hello interval regardless of whether BPDUs are received from root, allowing any switch to take an active role maintaining the topology
What if RSTP BPDUs aren’t received?
If three are missed in a row, the neighbor is considered down and the data for that neighbor is aged
What is the RSTP default hello interval?
2 seconds
What happens if both 802.1D and RSTP BPDUs are received?
the port will operate under 802.1D rules. If they are received on the same port, it will run 802.1D until the migration delay expires
What are the steps of RSTP convergence?
1- root bridge is elected, 2-the state of every switch port in the STP domain must be brought from blocking state to the appropriate state
What are the 3 RSTP port types?
edge, root, and point to point
RSTP edge port
only a single host connects . If one BPDU is received, it is no longer an edge port
RSTP point to point port
port that connects to another switch and becomes a designated port
How are RSTP point to point ports determined?
automatically by duplex mode in use. Full duplex are point ot point. Half duplex ports use traditional 802.1D convergence is used.
How is RSTP synchronization accomplished?
all non-edge ports are discarding. After the root bridge is identified, the port with superior BPDU becomes root
How does RSTP converge?
if a proposal is received, the recipient isolates, all nonedge ports blocked until proposal sent causing neighbors to synch, which propagates out in waves
How does RSTP identify a topology change?
only when a nonedge port transitions to forwarding
How is an RSTP edge port configured
with portfast
What is RPVST+?
an instance of RSTP running for each VLAN on the switch. Changing from PVST to RPVST+ is disruptive
When looking at the sh spanning tree output, what does P2P denote?
a point to point port type
When looking at the sh spanning tree output, what does P2P peer(STP) denote?
a point to point port type but the neighboring device runs traditional 802.1D STP
What does MSTP do?
Used when there are 1 or more VLANs mapped to a single STP instance
What do you need to determine to use MSTP?
the number of STP instances needed to support the desired topologies and whether to map a set of VLANs to each instance
Can MSTP interoperate with 802.1q and/or PVST+?
yes to both
What does MSTP consist of?
regions and instances
How is an instance defined?
by name, config revision, and instance to vlan mapping table
What is an IST instance?
within a single MST region, an IST instances runs to work out a loop free topology between links where CST meets the region boundary and all switches in the region. It runs at the boundary.
What is an MST instance?
The MST instance (MSTI) runs alongside the IST and represents an STP instance
How many MST instances can be in a region?
16 - IST gets MSTI 0, 1-15 are available for use. MSTIs are locally significant to the MST region
How do you implement MST?
MST attributes must be manually entereed on each switch in the region. They don’ t propagate like VTP.
What are the steps to configure MST?
1- enable MST, 2-enter MST config mode, 3-assign region name and region configuration rev, 4-map vlans to an MSTI, 5-show pending changes, 6- commit by exiting
