Hi Ismail,
Please find my answers inline.
Is Cisco per-vlan RSTP interoperable with MSTP , knowing that switch running MSTP is not a cisco switch ?
- MST maintains backward-compatibility with equipment that is based on
the(original) IEEE 802.1D spanning tree, with existing Cisco-proprietary
Multiple Instance STP (MISTP) , with existing Cisco per-VLAN spanning-tree plus(PVST+) and with rapid per-VLAN spanning-tree plus
(rapid PVST+).
- MSTP is fully compatible with RSTP bridges, in that an MSTP BPDU can be
interpreted by an RSTP bridge as an RSTP BPDU. This not only allows
compatibility with RSTP bridges without configuration changes, but also
causes any RSTP bridges outside of an MSTP region to see the region as a
single RSTP bridge, regardless of the number of MSTP bridges inside the
region itself.
Is there any restrictions & how it works ????
This table shows the support of MST in Catalyst switches and the minimum
software required for that support.
Catalyst Platform
MST with RSTP
Catalyst 2900 XL and 3500 XL
Not Available
Catalyst 2950 and 3550
Cisco IOSR 12.1(9)EA1
Catalyst 3560
Cisco IOS 12.1(9)EA1
Catalyst 3750
Cisco IOS 12.1(14)EA1
Catalyst 2955
All Cisco IOS versions
Catalyst 2948G-L3 and 4908G-L3
Not Available
Catalyst 4000, 2948G, and 2980G (Catalyst OS (CatOS))
7.1
Catalyst 4000 and 4500 (Cisco IOS)
12.1(12c)EW
Catalyst 5000 and 5500
Not Available
Catalyst 6000 and 6500 (CatOS)
7.1
Catalyst 6000 and 6500 (Cisco IOS)
12.1(11b)EX, 12.1(13)E, 12.2(14)SX
Catalyst 8500
Not Available
MSTP is a standard protocol so it does not differ than MSTP on non cisco switches, correct ???
When you connect the prestandard MST switch with the standard MST switch, you need to configure spanning-tree mst pre-standard in
the interface of the standard MST switch.
- Is Cisco per-vlan RSTP interoperable with standard RSTP ???
Yes.per-vlan RSTP is interoperable with open standard RSTP.
-RSTP is a standard 802.1w, but Cisco supports only Rapid PVST+ . In rapid-pvst+ there is an STP instance for each Vlan. .
-Cisco device sends 802.1w standard BPDU on native vlan as well. This was done for third party device interaction.
Is there any restrictions & how it works ????
In a network of Cisco switches connected through 802.1Q trunks, the switches
maintain one instance of STP for each VLAN allowed on the trunks. However,
non-Cisco 802.1Q switches maintain only one instance of STP for all VLANs
allowed on the trunks. When you connect a Cisco switch to a non-Cisco switch
through an 802.1Q trunk, the Cisco switch combines the STP instance of the
802.1Q VLAN of the trunk with the STP instance of the non-Cisco 802.1Q
switch. However, all per-VLAN STP information that is maintained by Cisco
switches is separated by a cloud of non-Cisco 802.1Q switches. The non-Cisco
802.1Q cloud that separates the Cisco switches is treated as a single trunk
link between the switches.
Therefore, Cisco devices interoperate with other vendors' 802.1w on access
ports and on the native VLAN of trunk ports. For all other VLANs, the other
switch will switch Cisco switch BPDUs like ordinary multicast frames. It
will not process them.
I hope this answers your questions.
-Somu Jayaraman
