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12. Describe Spanning Tree
Spanning tree used for loop prevention.
Loops can be absolutely disastrous in a bridged network for 2 primary
reasons: broadcast loops and bridge-table corruption.
STP decision sequence
- Lowest root BID
- Lowest path cost to root bridge
- Lowest sender BID
- Lowest port ID
3 steps of initial STP convergence
- Elect one root bridge
- Elect root ports
- Elect designated ports
STP states
- Standard states
- Forwarding: Sending / receiving user data
- Learning: Building bridging table
- Listening: Building "active" topology
- Blocking: Receives BPDUs only
- Disabled: Administratively down
- Cisco-specific states
- PortFast
- UplinkFast
STP timers
- Hallo time: Time between sending of configuration BPDUs by the
root bridge (default 2 seconds)
- Forward delay: Duration of listening and learning states (default
15 seconds)
- Max age: Time BPDU stored (default 20 seconds)
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46. Define LAN emulation.
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|
| OSI Layer | ATM
Layer | ATM
Sublayer
| Service
Specific (SS) | | Common Part | | Segmentation
and Reassembly | | Virtual Channel | | Virtual
Path | | Transmission Path | | Digital
Section | | Regenerator Section |
|
AAL (ATM Adaptation Layer):
| AAL | AAL1 | AAL2 | AAL3/4 | AAL5 |
|---|
| Class | A | B | C | D | | Timing | End-to-end | End-to-end | None | None | | Connection | Oriented | Oriented | Oriented | Less | | CBR
/ VBR | CBR | VBR | VBR | VBR | | Example | DSI,
E1, nx64 | packet, video, audio | FR,
X.25 | IP, SMDS |
AAL Function
AAL5
- Transfer most non-SMDS data and LANE.
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Exam
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47. Describe the LAN Emulation components.
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-
LEC (LAN Emulation Client)
-
LES (LAN Emulation Server)
- Performs MAC-to-ATM address resolution.
-
LECS (LAN Emulation Configuration Server)
-
BUS (Broadcast-and-Unknown Server)
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Exam
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48. Describe the start-up procedure of a LAN Emulation
Client.
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Catalyst 5000 architecture
- 5 ASICs: SAMBA, SAINT, SAGE, EARL, and Phoenix.
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Exam
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49. Describe how one LEC establishes communication with another
LEC.
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Catalyst 5000 architecture
- 5 ASICs: SAMBA, SAINT, SAGE, EARL, and Phoenix.
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Exam
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