TCP/IP: Illustrated, The Protocols

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Magic Frame: awake on LAN, it starts with ff/s, which followed by the destination mac address.

Pause Frame: sent to a fixed mac destination address.

Spanning Tree Protocol

Port state in bridge: blocking, listening, learning, forwarding and disabled.

After initialization, a port enters the blocking state. In this state, it does not learn addresses, forward frames, or transmit BPDUs, but it does monitor received BPDUs in case it needs to be included in the future on a path to the root bridge, in which case the port transitions to the listening state. In the listening state, the port is now permitted to send as well as receive BPDUs but not learn addresses or forward data. After a typical forwarding delay timeout of 15s, a port enters the learning state. Here it is permitted to do all procedures except forward data. It waits another forwarding delay before entering the forwarding state and commencing to forward frames.

Port Role: root port, designated port, alternate port, backup port.

A port may have the role of root port, designated port, alternate port, or backup port. Root ports are those ports at the end of an edge on the spanning tree headed toward the root. Designated ports are ports in the forwarding state acting as the port on the least-cost path to the root from the attached segment. Alternate ports are other ports on an attached segment that could also reach the root but at higher cost. They are not in the forwarding state. A backup port is a port connected to the same segment as a designated port on the same bridge. Thus, backup ports could easily take over for a failing designated port without disrupting any of the rest of the spanning tree topology but do not offer an alternate path to the root should the entire bridge fail.

ARP Cache的Flags Symbol: C: learned dynamically, M: entered manually, P: Published

ARP的timeout: Most implementations have a timeout of 20 minutes for a completed entry and 3 minutes for an incomplete entry.