From: Balaji Siva (bsivasub@gmail.com)
Date: Mon Feb 21 2005 - 21:25:22 GMT-3
That is correct behavior.
MST (MSTP is cisco pre-standard specific keyword) sends the IST
instance bpdu on all vlans. PVST sends unique BPDU on all the vlans.
Some discussions here
http://www.cisco.com/warp/customer/473/147.html#mst_region_world
hth
Balaji
On Mon, 21 Feb 2005 18:59:23 -0500, gladston@br.ibm.com
<gladston@br.ibm.com> wrote:
> I am facing this situation, related to MSTP on catalyst and IRB on router:
> CAT1 is connected to R7 through trunk connection.
>
> Vlan 73 connects R7 to R3 and Vlan 74 connects R7 to R4.
>
> There is only one catalyst, CAT1.
>
> CAT1 is configured to spanning-tree mode mstp.
>
> CAT1 port 0/7 is configured as following:
> switchport trunk encap dot
> switchport mode trunk
>
> R7 has two subinterfaces: fa0/0.73 and fa0/0.74.
> Both interfaces are configured to be part of bridge group 1:
>
> bridge irb
> bridge 1 protocol ieee
> bridge 1 route ip
> !
> int bvi 1
> ip ad 172.16.100.7
> int fa 0/0.73
> encap dot 73
> bridge-group 1
> !
> int fa 0/0.74
> encap dot 74
> bridge-group 1
>
> Bridge-group 1 is in blocking mode for int fa0/0.74 and forwarding mode for int fa 0/0.73.
>
> I was expecting CAT1 revert to 802.1D, as it just receives BPDU 802.1D from R7, but it does not.
> If I remove the MSTP configuration from CAT1 everything works as expected.
>
> It seems CAT1 sends the same BPDU through both Vlans over the trunk and receives it back from R7, forming a loop.
> If the mode is PVST, no problem.
>
> Any Comments?
>
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