Aamer Akhter wrote:
>
> the multicast mac is different (one protocol's bpdu's will get tunneled
> through the others domain). the multicast mac for 802.1d is
> 01-80-c2-00-00-00
> hello timer is 1 sec in dec rather than 2 sec
>
> afaik decnet isn't related in any wat to dec stp
The relationship is more to DECnet's predecessor,
LAT (local area transport). This was an ethernet-
based, bridged, non-routable protocol. So some way
was needed to have large bridged networks without
broadcast storms when a cabling error introduced
a loop.
DEC STP and IEEE802.1D are not interoperable but
this doesn't matter. All spanning tree does is
prevent loops, it has no effect on packet bridging
or MAC address learning once a bridge port is out
of the hold-down state. So you can run DEC STP on
one segment into a bridge and IEEE802.1D on another
segment into the same bridge. From memory, equipment
from Cisco that runs 'classic IOS' supports this.
Thanks to the neat seperation of forwarding and control,
in a modern switched network you can run LAT in a
IEE802.1Q VLAN with topology discovery by IEEE802.1D
spanning tree. DEC STP isn't needed at all.
The basic differences between DEC and IEEE spanning
tree is in parameter values:
PARAMETER IEEE DEC
Priority 32768 128 [ie: DEC uses 8 bits]
MaxAge 20 15
HelloTime 2 1
ForwardDelay 15 30
Note that the last three are reset from the root
bridge in both protocols. The default values of
the DEC timers allow some 'interesting' state
machine transitions.
Regards,
Glen
