الاخ كامل
متهيالى كلامك على حسب معلوماتي الصغيرة خطأ
pvst هي pervlan spanning tree
وهي ليست common spanning tree
common spt تكون عبارة عن spanning واحدة لكل الشبكة
اما pvst فتكون stp لكل vlan بمعنى ان لو عندك 10 vlan فى الشبكة سيكون هناك عشرة spanning tree
Common Spanning Tree
The IEEE 802.1Q standard specifies how VLANs are to be trunked between switches. It also specifies only a single instance of STP that encompasses all VLANs. This instance is referred to as the Common Spanning Tree (CST). All CST BPDUs are transmitted over trunk links using the native VLAN with untagged frames.Having a single STP for many VLANs simplifies switch configuration and reduces switch CPU
load during STP calculations. However, having only one STP instance can cause limitations, too. Redundant links between switches will be blocked with no capability for load balancing. Conditions
also can occur that would cause CST to mistakenly enable forwarding on a link that does not carry a specific VLAN, whereas other links would be blocked
خلاصة الكلام
بيقول ان cst هي عمل stp واحدة فقط لكل الشبكة حتى لو بها 1000 vlan
اما pvst
Per-VLAN Spanning Tree
Cisco has a proprietary version of STP that offers more flexibility than the CST version.
Per-VLAN Spanning Tree (PVST) operates a separate instance of STP for each individual VLAN. This allows the STP on each VLAN to be configured independently, offering better performance and tuning for specific conditions. Multiple spanning-trees also make load balancing possible over redundant
links when the links are assigned to different VLANs. One link might forward one set of VLANs,while another redundant link might forward a different set.
Because of its proprietary nature, PVST requires the use of Cisco Inter-Switch Link (ISL) trunking
encapsulation between switches. In networks where PVST and CST coexist, interoperability problems occur. Each requires a different trunking method, so BPDUs are never exchanged between STP types
وكما هو واضح فان هناك stp لكل vlan
والامر يكون بهذا الشكل
spanning-tree mode pvst
spanning-tree vlan 1,2,3,4,5,50,38,41,43,60,47,51,80,125,128 priority 8192
والامر الثاني لعمل root لل vlan المذكورة
اى لا نعمل السويتش كانه root لكل الشبكة
مع ملاحظة انه فى الشغل العملى يتم عمل encapsulation ب 802.1 q وليس isl كما هو مذكور
وهذا مطبق فعلا فى الشبكة التي اعمل عليها
ومذكور فى الكتب ان هناك pvst+ ولذلك للعمل على 802.1 q
وذلك للعمل والربط بين CSTو PVST
واعتقد ان pvst الموجود فى catalyst هو نفسه pvst+
Per-VLAN Spanning Tree Plus
Cisco has a second proprietary version of STP that allows devices to interoperate with both PVSTand CST.
Per-VLAN Spanning Tree Plus (PVST+) effectively supports three groups of STPoperating in the same campus network:
Catalyst switches running PVST
+
Catalyst switches running PVST
Switches running CST over 802.1Q
To do this, PVST+ acts as a translator between groups of CST switches and groups of PVSTswitches. PVST+ can communicate directly with PVST by using ISL trunks. To communicate with CST, however, PVST+ exchanges BPDUs with CST as untagged frames over the native
VLAN. BPDUs from other instances of STP (other VLANs) are propagated across the CST portions of the network by tunneling. PVST+ sends these BPDUs by using a unique multicast address so that the CST switches forward them on to downstream neighbors without interpreting them first. Eventually, the tunneled BPDUs reach other PVST+ switches where they are understood.
اما RAPID PVST فهي عبارة عن استخدام PVST ولكن نستخدمه معه rapid stp وذلك لتقليل الزمن الذي يأخذه المنفذ للتحول من listen الى learning الى forward
وهو يكون بمقدار 50 ثانية فى حالة عدم استخدام rapid stp اما عند استخدام rapistp مع اى نوع من انواع stp فأنه يتم تقليل الزمن بمقدار 30 ثانية
Rapid Per-VLAN Spanning Tree Protocol
In PVST+, one spanning tree instance is created and used for each active VLANthat is defined on the switch. Each STP instance behaves according to the traditional 802.1D
STP rules.
You can improve the efficiency of each STP instance by configuring a switch to begin using RSTP instead. This means that each VLAN will have its own independent instance of RSTP running on the switch. This mode is known as
Rapid PVST+ (RPVST+).
You need only one configuration step to change the STP mode and begin using RPVST+. You can use the following global configuration command to accomplish this:
Switch(config)# spanning-tree mode rapid-pvst
Be careful when you use this command on a production network because any STP process that is currently running must be restarted. This can cause functioning links to move through the traditional STP states, preventing data from flowing for a short time.
لمزيد من المعلومات موجود فى كورس bcmsn
اما الامر الذي استخدمه المهدس
spanning-tree extend system-id
فكما علمنا سابقا ان bridg id يتم تعيينه بواسطة جعل اول 2 بايت ل priorty و6 الباقيين ل mac address
اما باستخدام هذا الامر فاننا نجعل priorty يأخذ فقط 4 بنت من 16 بت الذين انو مخصصين ل priorty
و 12 الاخرين يكونون ل extended system id ويتم وضعهم يساو رقم vlan
الخلاصة
ممكن عمل اى stp بدون حذف هذا الامر
مع ملاحظة انه عند عمل root فأن هذا الامر سيزيد priorty بمقدار vlan
بمعنى اننا لو جعلنا priorty ل vlan 100 مثلا يساوي صفر فأننا عند عمل sh spanning tree سنرى priorty تساوي 100 وليست صفر كما وضعنها
ولو كانت priorty مثلا ل vlan 100 تساو مثلا 4100 فأننا سنراها تساوي 4200
ده فهمي للموضوع
والله تعالى اعلى واعلم ولو احد من الاخوة عنده تصحيح يا ريت ما يبخل بيه علينا
المفضلات