Filter
Top Products
DES-7200 Configuration Guide Chapter 10 MSTP Configuration
10-21
10.2.9 Understanding
ROOT Guard
In network design, root bridge and backup root bridge are always divided in the
same region. Due to error configuration of accendant and malicious attack in
the network, it is possible that root bridge receives configuration message of
higher priority and loses the current root bridge position, leading to error
turbulance of network topology, which Root Guard function can prevent from
occuring.
When enabling Root Guard, it enforces the port role of all the instances as
specified port. Once the port receives configuration message of higher priority,
Root Guard will set the interface as root-inconsistent (blocked). If there is no
configuration message of higher priority during the time long enough, the port
will be restored to be the original normal status.
You shall disable ROOT Guard function if this function results in the blocked
status for interfaces and it needs manual configuration to restore to the normal
status. You can use the command spanning-tree guard none in the interface
configuration mode to disable Root Guard function.
Caution
1. Incorrectly using ROOT Guard leads to network link
breakdown.
2. If you enable ROOT Guard on non-designated port, the
non-designated port will be enforced as designated port and
show BKN status(blocking status).
3. If MST0 enters BKN status because it receives configuration
message of higher priority on a port, ROOT Guard will enforce
the port in all the other instances to enter BKN status.
4. ROOT Guard or LOOP Guard takes effect at the same time.
That is , they can not both take effect at the same time .
5. The AutoEdge function is disabled when enabling the ROOT
Guard-enabled port.
10.2.10 Understanding
LOOP Guard
Due to breakdown of one-way link, root port or backup port becomes
designated port, being ready to forward because they can not receive BPDU,
causing the loop in the network, which Loop Guard function can prevent.
For the ports configured loop guard, if they can not receive BPDU, the port roles
will be migrated. However, the port state is always set as discarding till the port
receive BPDU again and recalculate spanning tree.