سؤال في stp

**محب الشبكات** · 30-08-2009, 18:23

السؤال الأول:
هل البورت الذي معمول له blocking يرسل bpdu?

السؤال الثاني
في الrstp :
متى نقول عن البورت أنه alternative port و backup port?

**احمد مهيدات** · 30-08-2009, 19:38

السلام عليكم ورحمة اللة وبركاتة
Q1: In the Blocking state, a port cannot receive or transmit data and cannot add MAC
addresses to its address table. Instead, a port is allowed to receive only BPDUs so that the
switch can hear from other neighboring switches.
Q2:
1- Alternate port—A port that has an alternative path to the root, different than the path the root
port takes. This path is less desirable than that of the root port. (An example of this is an
access-layer switch with two uplink ports; one becomes the root port, and the other is an
alternate port.)
2-Backup port—A port that provides a redundant (but less desirable) connection to a segment
where another switch port already connects. If that common segment is lost, the switch might
or might not have a path back to the root.

**احمد مهيدات** · 30-08-2009, 19:56

توضيح مع الصور...
https://www.cisco.com/en/US/tech/tk3...fa.shtml#roles

**محب الشبكات** · 01-09-2009, 04:06

طيب هل الكلام هذا صحيح والا لا

سمعت من يقول أن الalternative port هو ان السويتش عليه root port والآخر blocking ففي حالة حدث مشكله في الroot port فإن الblocking يتحول إلى root port

لكن بالنسبة لbackup port نفس الطريقه ولكن السويتش عليه designated port والآخر blocking ففي حالة حدث مشكله في الdesignater port يتحول الblocking إلى designated port

**one-zero** · 01-09-2009, 04:13

The backup port is a second best designated port for a segment on the designated switch. So when a switch delivers the designated port for the segment, it will have a backup port if this switch has another port connected to the same segment. In my opinion, the illustration above is not correct. Switch1 and Switch2 are connected with two segments! So there is no way that Switch2 will have a backup port; it only has one port to each of the segments.

The figure below depicts the port roles on the give network.

In case that a switch has a backup port to a segment, its guaranteed to be the second best designated port. It is connected to the same switch and hence will have the same (lowest) path cost towards and (if applicable) the same (lowest) Sender BID. When the original designated port becomes operational again, the original designated port will take up its role again as designated port.

In the figure below, Switch1 and Switch2 are connected with one segment. Switch1 and Switch2 each have two ports to that segment. Switch1 is the designated switch for that segment (it delivers the designated port) and will also have the backup port for that segment. Fa0/2 on Switch2 is now a non-designated port.

An alternate port is a second best root port for a switch. So when a switch looses the connectivity to the root; it will automatically select the alternate port as root port. The root port and the alternate port are on different segments.