Term
| if a Designated port suddenly receives a more attractive bpdu than what is currently saved on that port, what happens? |
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Definition
| The port will replace the BPDU and cycle the port through the listening and learning states. |
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Term
| what type of ports do not send configuration bpdus? |
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Definition
Root ports.
Designated ports send configuration bpdus.
Root ports send TCN bpdus. |
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Term
| if a new switch is added to a network segment and begins sending inferior bpdus, how do the other switches in the network respond? |
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Definition
| the new switch will send bpdus and enter the listening stage. The existing designated switch will immediately refute the bpdus and send the bpdu it has recorded for that particular port. |
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Term
| in what 3 cases are configuration bpdus sent? |
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Definition
1. when the hello timer expires.
2. when non-route bridges receive a configuration bpdu on their root port.
3. when a designated port hears an inferior configuration bpdu. |
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Term
| in what 3 cases are tcn's sent? |
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Definition
1. when a port is put in the forwarding state and the switch has at least one designated port.
2. when a port transitions from forwarding/learning to the blocking state.
3. when a tcn bpdu is received on a designated port, it is forwarded out the root port. |
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Term
| describe the stp message age field. |
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Definition
describes the length of time since the root bridge originated the bpdu.
Starts at 0 and is incremented by each switch.
Can be used to track the age of bpdus sent. |
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Term
| which 4 techniques are used to implement stp load-balancing? |
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Definition
1. root bridge placement
2. port priority
3. bridge priority
4. port cost |
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Term
| list 7 techniques to improve stp's convergence time. |
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Definition
1. tuning max age
2. tuning forward delay
3. lowering hello time
4. portfast
5. uplinkfast
6. backbonefast
7. disabling pagp on etherchannel-capable ports |
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Term
| what is the bpdu propagation delay? |
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Definition
The time it takes a bpdu to traverse the network, calculated using the following components:
1. lost messages
2. diameter
3. bpdu delay
4. hello timer |
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Term
| what is the message age overestimate? |
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Definition
| a rough estimate of how much the message age can be overestimated, as it is simply incremented by 1 second, by each switch. This helps to calculate the max age based ona network with a certain diameter. |
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Term
| how is the max age calculated? |
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Definition
| it is the sum of the bpdu propagation delay and the message age overestimate. |
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Term
| why will lowering the stp hello time not result in faster stp convergence? |
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Definition
| because the max age and forward delay will still be the same. |
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Term
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Definition
permits instant access to the network for end stations, without generating TCNs. Ignored on inter-switch trunk ports in 802.1D.
Spann portf
spann portf defa |
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Term
| describe uplinkfast, it's limitations and benefits. |
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Definition
allows leaf node switches to achieve instant failover to alternate root ports when direct root port failures occur. Will increase local priority and port costs to deter other switches from using the local switch for transit. Has the potential to change stp topology. bridge priority must be set to default before you enable.
spann uplink !!global!! |
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Term
| describe backbonefast, it's limitations and benefits. |
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Definition
reduces indirect failover performance by ignoring the max-age timer (reduction from 50 to 30 secs). Works on the concept that inferior bpdus are a signal that another switch may have lost its path to the root. Uses RLQ protocol to confirm.
Spann backb !!global!! |
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Term
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Definition
will filter inbound/outbound bpdus when configured at port level.
can prevent a host from participating in stp.
can be configured at interface level or globally with portfast.
Will send 11 bpdus and not filter inbound bpdus when configured globally.
Will only work on portfast ports when configured globally
spann bpduf enable !!int!!
spann portf bpduf defau !!global!! |
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Term
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Definition
disable the port if bpdus are received (loop prevention).
configured at interface level or globally with portfast.
Self-healing is possible with errdisable recovery.
Spann bpdug enable !!int!!
Spann portf defa !!global!!
Spann portf bpdug defa !!global!! |
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Term
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Definition
used on core/distribution, designated ports.
prevents a neighboring switch from becoming root, des port can't become root.
guards against attack or misconfig
puts port in root inconsistent
configured at interface level
spann guard root |
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Term
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Definition
similar to udld.
non-designated port enters a Loop Inconsistent state if BPDUs cease to be received.
prevents ports from becoming designated.
Self-heals when BPDUs are received.
Blocks per VLAN, applied to interface.
Apply to non-des interfaces for all possible topologies.
protection against stp failures.
uses stp bpdu.
spann guard loop |
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Term
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Definition
similar to loop guard.
blocks per port.
self-healing with err-disable.
protection against miswiring.
uses dedicated hello. |
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Term
| why can't rootguard and loop guard be used on the same port? |
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Definition
| Because they perform the opposite function. One prevents the port from becoming root, the other prevents the port from becoming designated. |
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Term
| why can't rootguard and portfast/bpdu guard be used on the same port? |
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Definition
| rootguard is designed for p2p switch links, portfast/bpdu guard are for edge ports. P2p switch links can't just be enabled immediately. |
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