Term
| What is the default STP bridge priority? |
|
Definition
|
|
Term
What is the priority for the VLAN below, assuming other switches are at default or are unknown?
(config)#spanning-tree vlan 100 root primary |
|
Definition
3K: 24576 if other switches are default or unknown.
4K, 6K: 8192 if other switches are default or unknown. |
|
|
Term
What is the bridge priority if this switch connects to an existing STP?
(config)#spanning-tree vlan 100 root primary |
|
Definition
| Current root priority - 4096 = 20480 (if previous root using default of 24576) |
|
|
Term
| What is the bridge priority for the following: (config)#spanning-tree vlan 100 root secondary |
|
Definition
28672 if others are default or unknown
Default is 32768
Secondary is 32768 - 4096 = 28672
Root is 32768 - 8192 = 24576 |
|
|
Term
| What are the 4 stages of 802.1d STP and how long do they take? |
|
Definition
Blocking (root election): 20 seconds
Listening (path election): 15 seconds
Learning: 15 seconds
Forwarding |
|
|
Term
| 802.1D: How does a bridge choose when it has two paths to the root? |
|
Definition
In order of preference:
1) Lowest cost to root
2) Lowest port priority
3) Lowest port number |
|
|
Term
| Who becomes the root bridge in 802.1D? |
|
Definition
Bridge with lowest priority.
If priorities are equal, use lowest MAC. |
|
|
Term
| What is the default cost for 100M link in 802.1D? |
|
Definition
|
|
Term
| What is MaxAge in 802.1D? |
|
Definition
10 * Hello = 20 seconds
This is the duration of root election and the amount of time a switch will ignore bad BPDUs or timeout a root port that has stopped receiving BPDUs. |
|
|
Term
| What etherchannel protocol uses the options "auto" and "desirable"? |
|
Definition
|
|
Term
| What etherchannel protocol uses the options "active" and "passive"? |
|
Definition
|
|
Term
| What is the default load balancing scheme for etherchannel? |
|
Definition
| Source and destination IP |
|
|
Term
| Will an etherchannel form if one side is configured for PagP and the other is not? |
|
Definition
| Yes, unless the "non-silent" option is configured. |
|
|
Term
| What are the three port states in 802.1w? |
|
Definition
Discarding
Learning
Forwarding |
|
|
Term
| What are the two new port roles introduced in 802.1w? |
|
Definition
- Alternate (to Root)
- Backup (to Designated)
802.1d defined three: root, designated, blocked |
|
|
Term
| What defines a topology change in 802.1w? |
|
Definition
| A non-edge port moving to the forwarding state. |
|
|
Term
| What vlans are not eligible for VTP pruning? |
|
Definition
1, 1002-1005
1006 - 4094 are not supported with VTP |
|
|
Term
| Is VTP enabled by default? Is VTP pruning enabled by default? |
|
Definition
| VTP is enabled by default, VTP pruning is not. |
|
|
Term
| If one side is configured for "mode trunk" and the other side is "mode dynamic auto", will a trunk form? |
|
Definition
Yes.
"mode trunk" will send DTP (but it doesn't require it to form a trunk). |
|
|
Term
| If one side is configured for "mode trunk, nonnegotiate" and the other side is "mode dynamic auto", will a trunk form? |
|
Definition
| No. "dynamic auto" will not initiate DTP but it requires that DTP succeed. "non-negotiate" means other sides will not send DTP. |
|
|
Term
| Which IEEE standard defines STP? |
|
Definition
|
|
Term
| In 802.1D, what is the port called that is receiving the best BPDUs? |
|
Definition
| The Root Port is the port on the switch that receives the best BPDUs. |
|
|
Term
| In 802.1D, what is the name of the port that can send the best BPDU on the segment? |
|
Definition
| The Designated Port can send the best BPDU on the segment |
|
|
Term
| In STP, what is the name of any port that is not designated or root and receives better BPDUs than it can send? |
|
Definition
|
|
Term
| What is the function of the Blocking phase in STP? |
|
Definition
| The root is elected in the blocking phase |
|
|
Term
| Can bridges learn MAC addresses in the Blocking phase of STP? |
|
Definition
| No, MAC addresses are not learned in the blocking phase. |
|
|
Term
| In what phase of STP does path election occur? |
|
Definition
| Path election occurs in the Listening Phase of STP |
|
|
Term
| At what link speed is the 16 bit short mode cost inaccurate for STP? |
|
Definition
| Cost is 10 for 10G (which is inaccurate as it is higher than the 1G cost of 4). |
|
|
Term
| What is the cost of a 100M link in 32 bit Long Mode Cost? |
|
Definition
| In Long Mode, the cost of a 100M link is 200000. |
|
|
Term
| What does the command "spanning-tree pathcost method long" do? |
|
Definition
| Changes to 32 bit path cost |
|
|
Term
| What determines which switch will forward frames to/from this segment when two switches are connected to the same downstream LAN? |
|
Definition
Lowest Root Path Cost
Lowest Sender Bridge ID
Lowest Sender Port ID |
|
|
Term
| How long is the fwd-delay timer and what 802.1D phase does it occur in? |
|
Definition
| 15 seconds, Learning phase |
|
|
Term
| In a stable STP topology, who originates BPDUs? |
|
Definition
| Only the root originates BPDUs. non-root switches forward those BPDUs. |
|
|
Term
| In what STP phase are MAC addresses learned and put in address tables? |
|
Definition
|
|
Term
| In STP, when will a non-root bridge send a BPDU? |
|
Definition
| When the topology changes (link down), the directly connected bridge sends a TCN BPDU to the root. |
|
|
Term
| What does a designated bridge do when it receives a TCN BPDU from a downstream switch? |
|
Definition
| The designated bridge sends a TCN-ACK to the downstream bridge and a TCN BPDU to the root bridge. |
|
|
Term
| What is the ultimate purpose of a TCN BPDU in STP? |
|
Definition
| To accelerate the MAC aging process for a period of time. |
|
|
Term
| What does the root do when it receives a TCN BPDU? |
|
Definition
| The root starts sending BPDUs with the TC bit set. |
|
|
Term
| What do bridges do when they are receiving TC BPDUs from the root? |
|
Definition
| They age out MAC address table entries after fwd-delay time (15 seconds) and relearn MACs for fwd-delay+macage = 35 seconds |
|
|
Term
| When a switch stops receiving BPDUs on its root port, how long does it wait before it recalculates STP? |
|
Definition
|
|
Term
| What is the IEEE standard for RSTP? |
|
Definition
802.1w
It's "W"ascally rapid. |
|
|
Term
| What is the normal bridge ID? |
|
Definition
| Bridge priority (2 bytes) + MAC (6 bytes) |
|
|
Term
| What is the extended bridge ID? |
|
Definition
| Bridge Priority (4 bits) + VLAN (12 bits) + MAC (6 bytes) |
|
|
Term
| In 802.1D, how many STPs will you have if you have 10 VLANs. |
|
Definition
| One. 802.1D define a Common Spanning Tree (CST) for all VLANs. |
|
|
Term
| In 802.1D, who sets the timers for BPDUs? |
|
Definition
| The root switch. Settings on non-root switches don't matter. |
|
|
Term
| In 802.1D, BPDUs are tagged or untagged? |
|
Definition
|
|
Term
| In 802.1w, what kind of port is blocked because it receives better BPDUs from another bridge on the same segment? |
|
Definition
| Alternate port (offers alternate path to root) |
|
|
Term
| In 802.1w, what kind of port receive better BPDUs from another port on its own bridge on the same segment? |
|
Definition
| A Backup port is a backup for the designated port. |
|
|
Term
| What are the three link types in 802.1w? |
|
Definition
1) Edge: single host, no STP participation, same as portfast
2) Shared: connect to other switch via hub (rarely used)
3) point-to-point: Designated port |
|
|
Term
| How often do 802.1s bridges send BPDUs? |
|
Definition
|
|
Term
| Does an RSTP bridge need to receive a BPDU from the root in order to send one? |
|
Definition
| No, RTSP bridges forward BPDUs every 2 seconds regardless of what the root does. |
|
|
Term
| How many BPDUs in a row can be missed before an RSTP bridge ages out BPDU information from that neighbor? |
|
Definition
|
|
Term
| RSTP BPDUs are marked as what version? |
|
Definition
|
|
Term
| In RSTP, what does a bridge do if it receives an inferior BPDU on a port? |
|
Definition
| An RSTP bridge will immediately send a BPDU with root info when an inferior BPDU is received. |
|
|
Term
| In STP, what does a bridge do if it receives an inferior BPDU on a port? |
|
Definition
| It will wait 20 seconds (MaxAge) before aging out BPDU info and transitioning to Listening phase. |
|
|
Term
| Which protocol sends a BPDU with proposal bit when it comes up? |
|
Definition
|
|
Term
| What two things does an RSTP switch do when it receives a better BPDU from a new neighbor? |
|
Definition
1) Block its former root port
2) Explicitly authorizes neighbor to put port in forwarding state by sending proposal BPDU with agree bit set. |
|
|
Term
| In RSTP, is a link going down a topology change? |
|
Definition
| No (but it is in STP. Only a non-edge port transitioning to forwarding is considered a topology change in RSTP. |
|
|
Term
| What happens when an RSTP bridge detects a topology change in RSTP? |
|
Definition
1) Bridge starts TCWile Timer (2x hello = 4 seconds) on designated and root ports.
2) Flushes MAC associated with these ports
3) Sends BPDUs with TC bit.
4) Neighbors receiving BPDU with TC bit flood it. |
|
|
Term
| What must all switches agree on in the same MST region? |
|
Definition
1) MST config name
2) rev number
3) instance to VLAN maping table |
|
|
Term
|
Definition
| A group of bridges with the same MST configuration. |
|
|
Term
| How many MST instances are allowed per region? |
|
Definition
|
|
Term
| What instances sends and receives BPDUs in MST? |
|
Definition
| Only Instance 0 (Internal Spanning Tree-IST). |
|
|
Term
| What do MST BPDUs contain? |
|
Definition
| A digest of VLAN to instance mapping. |
|
|
Term
| How many VLANs can be mapped in MST? |
|
Definition
|
|
Term
| What is the IEEE standard for MST? |
|
Definition
|
|
Term
| What happens when a BPDU is received on a portfast port? |
|
Definition
| Portfast functionality is lost and the port begins STP. |
|
|
Term
| What STP features allows a switch to immediately change to a redundant link if the directly-connected root port fails? |
|
Definition
|
|
Term
| What STP stages does Uplink fast skip? |
|
Definition
|
|
Term
| What does configuring Uplink Fast do to priority and port cost? |
|
Definition
| Increases priority to 49152 and increment port cost by 3000 to discourage downstream switches from going through it. |
|
|
Term
| In uplink fast, how does downstream switch tell upstream switch that addresses are reachable on a new link? |
|
Definition
| Downstream switch sends dummy multicast to 0100.0ccd.cdcd for each MAC in the CAM table at a rate of 150 per second. |
|
|
Term
| To be effective, where should Uplink Fast be configured? |
|
Definition
| On all switches, all VLANs. |
|
|
Term
| What are two indications of an indirect link failure? |
|
Definition
| Missed Hello or inferior bpdu |
|
|
Term
| What is the convergence delay for an indirect link failure with and without backbone fast configured? |
|
Definition
50 seconds without backbone fast
30 seconds with backbone fast
- Switch that receives inferior BPDU on root port will switch to alternate port immediately (not wait 10 X Hello timer = 20 seconds) and begin listening and learning.
- Switch that misses a BPDU on root port will send RLQ query (all the way to root) to see if path to root exists first.
|
|
|
Term
| What feature allows multiple links to be treated as a single link from an STP perspective? |
|
Definition
|
|
Term
| What must bundled ports have in common? |
|
Definition
| Speed, duplex and interface type |
|
|
Term
| What must bundled trunk ports have in common? |
|
Definition
| native vlan, allowed vlans, encapsulation, DTP mode, STP port cost per VLAN |
|
|
Term
| What must non-trunk bundled ports have in common? |
|
Definition
|
|
Term
| For bundled routed ports, where is the iP address configured |
|
Definition
| IP address is configured on port channel interface (not physical interface) |
|
|
Term
| What are the limitations of an etherchannel participating in a SPAN sessions? |
|
Definition
| An etherchannel can be the source port for SPAN, but not the destination |
|
|
Term
| What will happen if a physical port that is part of an etherchannel is assigned as the destination of a SPAN session? |
|
Definition
| The port will be removed from the group when span is on. |
|
|
Term
| In an etherchannel, what link(s) does STP run on? |
|
Definition
| STP runs on the first physical interface |
|
|
Term
| How can traffic be load-balanced on an etherchannel? |
|
Definition
| L2/L3 and/or L4 headers (depends on switch and code version) |
|
|
Term
| What fields would not be a good choice for load balancing on an access switch etherchannel? |
|
Definition
| Destination IP and MAC (because most traffic from endpoints goes to default gateway which has same MAC and IP). |
|
|
Term
| How is inbound multicast and broadcast traffic handled on an etherchannel? |
|
Definition
| Inbound multicast and broadcast are not forwarded back out any other links on the etherchannel? |
|
|
Term
| What command would statically configure a port channel without using a dynamic protocol? |
|
Definition
|
|
Term
| What is the LACP equivalent of PagP's "auto" setting in the channel-group 1 auto command? |
|
Definition
| Like PagP's "auto", LACP's "passive" waits for the other side to send a message first. |
|
|
Term
| Does "channel-group 1 active" enable LACP or PagP? |
|
Definition
|
|
Term
| Does "channel-group 1 desirable" enable LACP or PagP? |
|
Definition
| "desirable" is a PagP setting |
|
|
Term
| What are the recommended settings for PagP and LACP? |
|
Definition
| "desirable" (PagP) and "active" (LACP) will ensure the portchannel gets formed dynamically |
|
|
Term
| What does IEEE 802.1AD define? |
|
Definition
| Link Aggregation Control Protocol (LACP) |
|
|
Term
| If a port is configured for "channel-group 1 desirable", what will the switch do if no response is received to pagp messages? |
|
Definition
| It will form a port-channel anyway after 15 seconds of silence. |
|
|
Term
| "channel-group 1 desirable non-silent", what will the switch do if no response is received to pagp messages? |
|
Definition
| The switch must receive pagp from the other side before it will form portchannel |
|
|
Term
| How many links can be configured and how many used at any one time for a LACP portchannel? |
|
Definition
| 16 can be defined but only 8 will be used at one time (others are hot standby) |
|
|
Term
| Which switch makes decisions about which ports are used in LACP portchannels? |
|
Definition
| Switch with the lowest system priority |
|
|
Term
| How are ports selected in LACP? |
|
Definition
| Lowest priority or lowest port number if priority the same. |
|
|
Term
| How does global bpduguard config defer from port config? |
|
Definition
| Global config "spanning-tree portfast bpduguard disable" only applies to portfast ports. Port config "spanning-tree bpduguard enable" applies regardless of portfast |
|
|
Term
| What happens on a port where rootguard is configured when a superior bpdu is received? |
|
Definition
| Port is put in root inconsistent state and all traffic is blocked. |
|
|
Term
| If a rootguard port stops receiving superior bpdus, what happens? |
|
Definition
| If superior bpdu stops, root guard allows STP to continue (no err-recovery config required) |
|
|
Term
| What are three STP protection mechanisms for access switches? |
|
Definition
bpduguard
bpdu filter
root guard |
|
|
Term
| What are two STP protection features for trunk ports? |
|
Definition
|
|
Term
| Where should loop guard be deployed? |
|
Definition
| Root and alternate root ports on trunk ports |
|
|
Term
| How does loop guard prevent loops? |
|
Definition
| Prevents root ports from going through STP if BPDUs stop. Port will be moved to loop inconsistent state. |
|
|
Term
| Does loop guard affect the whole port? |
|
Definition
| No, loop guard only affects VLANs. |
|
|
Term
| Why is UDLD better on port channels? |
|
Definition
| UDLD only impacts a single link. Loopguard impacts the whole port channel. |
|
|
Term
| Name two advantages of loopguard over UDLD |
|
Definition
Loopguard is faster and can detect problems with STP.
UDLD detects problems with UDLD packets (STP may be broken when UDLD is not) |
|
|
Term
|
Definition
| Each switch sends an L2 UDLD frame, expects an echo. |
|
|
Term
| What's the difference between normal and aggressive UDLD mode? |
|
Definition
| Normally, UDLD only disables itself. Aggressive UDLD disables both sides. |
|
|
Term
| Is VTP pruning enabled or disabled by default? |
|
Definition
| VTP Pruning is disabled by default. |
|
|
Term
| What 4 errors are indicators of duplex mismatch? |
|
Definition
| FCS, CRC, alignment, or runts |
|
|
Term
| In RSTP and 802.1D, what ports send BPDUs? |
|
Definition
| Only Designated Ports. BPDUs are never sent on root ports or blocked ports. |
|
|
Term
| What comes first, STP, PagP/LACP, DTP? |
|
Definition
| STP doesn't run until port type is decided, so: DTP -> PagP/LACP -> STP |
|
|
Term
| What is the minimum amount of information that must be configured for a VTP update to be sent? |
|
Definition
| At least one VTP server must have a domain name configured. |
|
|
Term
| True or false: VTP sends updates out all ports. |
|
Definition
| False -- VTPp sends updates out all active trunk interfaces only. |
|
|
Term
| How can VTP DOS attacks be mitigated? |
|
Definition
| Mitigate VTP DoS attacks by configuring VTP passwords (MD5). |
|
|
Term
| Can a VTP server updates its VLAN config with a VTP advertisement from a client? |
|
Definition
|
|
Term
| Which trunk protocol adds a 26 byte header and 4 byte CRC? |
|
Definition
|
|
Term
| Which trunk protocol uses the source address of the trunking device and a multicast destination address? |
|
Definition
|
|
Term
| Which trunk protocol inserts a 4 byte header/tag? |
|
Definition
|
|
Term
| What does an Ether frametype of 0x8100 indicate? |
|
Definition
| Frametype 0x8100 indicates that an 802.1Q header follows. |
|
|
Term
| Which switchport mode always trunks and sends DTP to help other side trunk? |
|
Definition
|
|
Term
| What switchport mode initiates DTP and only trunks if DTP succeeds? |
|
Definition
| switchport mode dynamic desirable |
|
|
Term
| What does "switchport nonnegotiate" do? |
|
Definition
|
|
Term
| What switchport mode never trunks and sends DTP to help other side not trunk either? |
|
Definition
|
|
Term
| Which trunk protocol supports extended range VLANs today? |
|
Definition
| Both ISL and 802.1Q support extended range VLANs (in the past, ISL only did normal range but it has changed.) |
|
|
Term
| What is the range of extended VLANs? |
|
Definition
|
|
Term
| Do CDP and VTP pass inside QinQ tunnels? |
|
Definition
| Yes, CDP and VTP pass in QinQ tunnels |
|
|
Term
| Will an 802.1Q trunk form if the native VLAN is different? |
|
Definition
| No, native VLAN must match for 1Q trunk to form. |
|
|
Term
| Is VLAN 4095 user configurable? |
|
Definition
| No, like VLAN 0, VLAN 4095 is reserved for system use. |
|
|
Term
| What does switchport mode dot1qtunnel do? |
|
Definition
|
|
Term
| What 3 PagP mode combinations will result in the formation of an Etherchannel? |
|
Definition
auto-desirable
desirable-desirable
on-on |
|
|
