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51 Cards in this Set
- Front
- Back
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what are the three major problems loops cause? |
broadcast storms, CAM table instability, multiple frame transmission |
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Describe CAM table instability |
when a broadcast storm causes a switch to continually receive copies of a frame from two or more different source IF's, it floods the CAM table with new entries, making the sender of the frame unreachable) |
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Describe the problem of multiple frame transmission |
receiving node can't make sense of the data it's being sent as it continually receives the same frame repeatedly |
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Describe a switches convergence process? |
A switch will notice if its root port does not send a BPDU within the maxage timer or if the interface goes down, at which point it will listen for other superior BPDU's and react accordingly |
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What two temporary states must a blocking port go through to become a forwarding port? |
listening, learning |
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Describe listenign state |
Does not record macs entering interface nor process frames. Any entries in the CAM table it does not recieve frames from during this time will be removed |
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Describe learning state |
Still does not forward out interface but will begin to learn macs |
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What are the different versions of STP |
PVSTP (per vlan), RSTP, RPVST (per vlan, |
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What command sets STP version? |
spanning-tree mode |
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How is the BID divided? |
Priority field (16bit); switch mac address (6 byte) |
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how is the priority field divided on cisco switches? |
4 bit priority field, 12 bit system id extension field (corresponds to # of vlans cisco switches support, with the first 4 bits representing multilpes of 4096) |
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What is the default priority base value on cisco devices? |
32, 768 |
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what number must priority field be set to multiples of? |
4096 |
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What are the default costs? |
10 = 100, 100 = 19, 1gbps = 4, 10gbps = 2 |
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How can you change the priority field on cisco switches? |
spanning-tree vlan priority |
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What coes spanning-tree vlan root primary set the priority to? |
24, 576 |
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What does spanning-tree vlan root secondary set the priority to? |
28,672 |
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What is portfast? |
Portfast causes ports to skip learning/listenign states on ports that won't have switches connected to them |
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how do you enable/disable portfast per if? |
(no) spanning-tree portfast |
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how do you enable/disable portfasst globaly? |
spanning-tree portfast default spanning-tree portfast disable (per if) |
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what is BPDUGuard? |
Blocks if from recieving bpdu's to prevent unwanted switches from connecting |
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hwo do you enable bpdu guard per if? |
spanning-tree bpduguard disable|enable
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how do you enable bpdu guard globally? |
spanning-tree bpduguard default |
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What is an etherchannel? |
An etherchannel is a set of interfaces to be treated as one, where stp states are shared, and a broadcast recieved in one isn't forwarded out the other (and cam entries list it vs a specific if) |
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How do you put an interface into an etherchannel? |
channel-group number mode on |
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What does PaGP stand for? |
Port Aggregation protocol (cisco) |
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What does LACP stand for? |
Link Aggregation protocol (IEEE) |
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What are the attributes for a PaGP interface? |
desirable|auto |
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What are the attributes for an LACP interface? |
active|passive |
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Does an etherchannel number on one end of a link have to match that on the other? |
No |
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If one etherchannel is configured manually, can the other be set dynamically? |
No |
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Can one etherchannel use LACP while the other PAGP? |
no |
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How do you set an interface to negotiate etherchannel with PAGP? |
channel-group *number* mode desirable|auto |
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how do you set an interface to negotiate etherchannel with LACP? |
channel-gropu *number* mode active|passive |
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What will show spanning-tree vlan * do/ |
see root id, bridge id, their macs, timers, dp's, rp's |
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What will show spanning-tree root show? |
shows root id, cost, and port for each vlan |
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what will show spanning-tree vlan * bridge do? |
show priority broken down into priority & vlan |
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how can one interactively show stp changes? |
debug spanning-tree events |
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How is the root port determined? |
Whoever has the lowest cost |
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What are the tie breakers for RP? |
lowest BID lowest priority lowest internal port # |
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How is DP determined? |
BPDU with lowest cost |
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What timer determines how long listening and learning states last? |
forward delay timer |
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What are tie breakers for DP? |
BID, port priority, port # |
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What attributes must be up for an etherchannel to stay up (independent of interfaces) |
manual/pagp/lacp auto on both switches passive on both switches |
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What attributes must be shared for all individual interfaces in an etherchannel to not be err-disabled or similar? |
speed, duplex, access/trunk, access vlan, native vlan, allowed vlans, |
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what attributes must be share dby all individual interfaces on the same switch specifically to work |
STP port cost & priority settings |
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what is the range of possible priorities? |
0-255 |
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How do you set port priority? |
spanning-tree vlan * port-priority |
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how do you set port cost? |
spaning-tree cost |
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How can you see etherchannel status? |
show etherchannel summary |
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To troubleshoto etherchannel, what must we check? |
1) That both sides of switch agree on manual/LACP/PAGP and that LACP/PAGP aren't both passive or both auto 2) that speed, duplex, access/trunk, allowed/native vlans agree |
