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Understanding Linux Network Internals 2005 phần 4

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Cây cầu gốc làm cho chắc chắn rằng mỗi cầu nối trong mạng đến để biết về một sự thay đổi cấu trúc liên kết khi một người xảy ra (xem phần "Cấu trúc liên kết Thay đổi"). Lưu ý rằng việc lựa chọn các tiểu bang cổng và vai trò (và do đó của các liên kết đó phải được kích hoạt hay vô hiệu hóa) phụ thuộc vào vị trí của cây | This document was created by an unregistered ChmMagic please go to http www.bisenter.com to register it. Thanks The root bridge makes sure each bridge in the network comes to know about a topology change when one occurs see the section Topology Changes . Note that the selection of the port states and roles and therefore of the links that should be enabled or disabled depends on the location of the root bridge in the topology this is because first you select the root bridge and then you build the best tree based on that. 15.3.2. Designated Bridges While each tree has only one root bridge there is one designated bridge for each LAN which becomes the bridge all hosts and bridges on the LAN use to reach the root. The designated bridge is chosen by determining which bridge on the LAN has the lowest path cost to the root bridge. Thus using Figure 15-2 as an example The links in the figure are not assigned costs. You can assume their costs to be 1 and therefore the path cost to be the hop count. This is just an example 1 is not the default cost assigned to links. In the A3-D2 LAN D2 is the designated bridge. In the D2-C2 LAN C2 is the designated bridge. 15.3.3. Spanning Tree Ports We introduced the root and designated bridge s roles in the previous sections. Let s see here what states and roles can be assigned to a bridge port. 15.3.3.1. Port states An STP port is a port in a bridge that runs the STP. This port will process ingress BPDUs and transmit BPDUs according to the rules in the section When to Transmit Configuration BPDUs An STP port can be in any of the following states Disabled The port is shut down through administrative action it does not receive or transmit any traffic. Blocking The port is up but the STP has blocked it. It cannot be used to forward any data traffic. Listening The port is enabled but it cannot be used to forward any data traffic. Simpo PDF Merge 9Ud Split Uuregistered Versiou - Pttp www.simpopdf.com This document was created by an .