[Bridge] Invalid BPDU transmission?

[Bridge] Invalid BPDU transmission?

[Rodolfo Giometti]

Hello,

in function STP_transmit_check_conditions (rstplib/transmit.c) the
case:

    case IDLE:
      if (!port->helloWhen) return STP_hop_2_state (this,
      TRANSMIT_PERIODIC);
      if (!port->sendRSTP && port->newInfo &&
          (port->txCount < TxHoldCount) &&
          (port->role == DesignatedPort) &&
          port->helloWhen)
        return STP_hop_2_state (this, TRANSMIT_CONFIG);
      if (!port->sendRSTP && port->newInfo &&
          (port->txCount < TxHoldCount) &&
          (port->role == RootPort) &&
          port->helloWhen)
        return STP_hop_2_state (this, TRANSMIT_TCN);
      if (port->sendRSTP && port->newInfo &&
          (port->txCount < TxHoldCount) &&
          ((port->role == RootPort) ||         <----
           (port->role == DesignatedPort)))
        return STP_hop_2_state (this, TRANSMIT_RSTP);
      break;

states that a RSTP bpdu can be transmitted even throught a RootPort
which, IMHO, is not correct... only topology change BPDU should be
sent over the RootPort. That's why I suggest to remove the line with
the arrow (<----).

Comments? :)

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail: giometti@enneenne.com
Linux Device Driver                          giometti@linux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
Freelance ICT Italia - Consulente ICT Italia - www.consulenti-ict.it

Re: [Bridge] Invalid BPDU transmission?

[Srinivas M.A.]

Both CONFIG and TCN BPDUs are used only in STP compatibility mode. In
RSTP mode, the BPDUs sent in both directions are RSTP BPDUs. So they
can be sent on the root port.

For a description of how topology changes are handled, see the section
titled "New Topology Change Mechanisms" in
http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml

Is this causing any particular issue?

On Tue, Oct 5, 2010 at 3:24 PM, Rodolfo Giometti <giometti@enneenne.com> wrote:
> Hello,
>
> in function STP_transmit_check_conditions (rstplib/transmit.c) the
> case:
>
>    case IDLE:
>      if (!port->helloWhen) return STP_hop_2_state (this,
>      TRANSMIT_PERIODIC);
>      if (!port->sendRSTP && port->newInfo &&
>          (port->txCount < TxHoldCount) &&
>          (port->role == DesignatedPort) &&
>          port->helloWhen)
>        return STP_hop_2_state (this, TRANSMIT_CONFIG);
>      if (!port->sendRSTP && port->newInfo &&
>          (port->txCount < TxHoldCount) &&
>          (port->role == RootPort) &&
>          port->helloWhen)
>        return STP_hop_2_state (this, TRANSMIT_TCN);
>      if (port->sendRSTP && port->newInfo &&
>          (port->txCount < TxHoldCount) &&
>          ((port->role == RootPort) ||         <----
>           (port->role == DesignatedPort)))
>        return STP_hop_2_state (this, TRANSMIT_RSTP);
>      break;
>
> states that a RSTP bpdu can be transmitted even throught a RootPort
> which, IMHO, is not correct... only topology change BPDU should be
> sent over the RootPort. That's why I suggest to remove the line with
> the arrow (<----).
>
> Comments? :)
>
> Ciao,
>
> Rodolfo
>
> --
>
> GNU/Linux Solutions                  e-mail: giometti@enneenne.com
> Linux Device Driver                          giometti@linux.it
> Embedded Systems                     phone:  +39 349 2432127
> UNIX programming                     skype:  rodolfo.giometti
> Freelance ICT Italia - Consulente ICT Italia - www.consulenti-ict.it
> _______________________________________________
> Bridge mailing list
> Bridge@lists.linux-foundation.org
> https://lists.linux-foundation.org/mailman/listinfo/bridge
>

Re: [Bridge] Invalid BPDU transmission?

[Rodolfo Giometti]

On Tue, Oct 05, 2010 at 06:10:32PM +0530, Srinivas M.A. wrote:
> Both CONFIG and TCN BPDUs are used only in STP compatibility mode. In
> RSTP mode, the BPDUs sent in both directions are RSTP BPDUs. So they
> can be sent on the root port.
> 
> For a description of how topology changes are handled, see the section
> titled "New Topology Change Mechanisms" in
> http://www.cisco.com/en/US/tech/tk389/tk621/technologies_white_paper09186a0080094cfa.shtml
> 
> Is this causing any particular issue?

Yes. By using the following connection:

  +---------------+        +----------------------+
  | EXTRA bridge  O <----> O(eth5) bridge on test |
  +---------------+        |      (eth0) (eth1)   |
                           +--------O------O------+
                                    ^      ^
                                    |      |
                                    +------+

where «EXTRA bridge» is a rstp bridge acting as root bridge and NOT
running rstpd (but a proprietary rstp implementation), while «bridge
on test» is my bridge running rstpd.

«EXTRA bridge» sends to «bridge on test» the following BDPU:

   01 80 c2 00 00 00 00 02 3e 99 ba 1c 00 27 42 42
   03 00 00 02 02 7e 80 00 00 02 3e 99 ba 1c 00 00
   00 00 80 00 00 02 3e 99 ba 1c 80 01 00 00 14 00
   02 00 0f 00 00

and «bridge on test» replies on «eth5», which is its root port.

Without my modification «bridge on test» is unstable, in fact the
states of eth0 and eth1 ports doesn't fit to Fwd end Blk but they
change in a strange manner and don't stabilize... also opening and
closing the loop cause more instability and the bridge takes very long
time before changing its ports states!

By adding my modification everything works well.

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail: giometti@enneenne.com
Linux Device Driver                          giometti@linux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
Freelance ICT Italia - Consulente ICT Italia - www.consulenti-ict.it

Re: [Bridge] Invalid BPDU transmission?

[Rodolfo Giometti]

On Wed, Oct 06, 2010 at 05:32:32PM +0200, Rodolfo Giometti wrote:
> 
> «EXTRA bridge» sends to «bridge on test» the following BDPU:
> 
>    01 80 c2 00 00 00 00 02 3e 99 ba 1c 00 27 42 42
>    03 00 00 02 02 7e 80 00 00 02 3e 99 ba 1c 00 00
>    00 00 80 00 00 02 3e 99 ba 1c 80 01 00 00 14 00
>    02 00 0f 00 00

Sorry, the correct BDPU is the following:

01 80 c2 00 00 00 00 01  f4 33 1c 54 00 27 42 42
03 00 00 02 02 7e 00 00  00 01 f4 7e a2 57 00 00
00 00 00 00 00 01 f4 7e  a2 57 83 4e 00 00 0a 00
01 00 0f 00 00

Ciao,

Rodolfo

-- 

GNU/Linux Solutions                  e-mail: giometti@enneenne.com
Linux Device Driver                          giometti@linux.it
Embedded Systems                     phone:  +39 349 2432127
UNIX programming                     skype:  rodolfo.giometti
Freelance ICT Italia - Consulente ICT Italia - www.consulenti-ict.it

Re: [Bridge] Invalid BPDU transmission?

[Srinivas M.A.]

> Sorry, the correct BDPU is the following:
>
> 01 80 c2 00 00 00 00 01  f4 33 1c 54 00 27 42 42
> 03 00 00 02 02 7e 00 00  00 01 f4 7e a2 57 00 00
> 00 00 00 00 00 01 f4 7e  a2 57 83 4e 00 00 0a 00
> 01 00 0f 00 00

The 7e in 00 00 02 02 7e ... is a flags value with the proposal flag
set (mask 0x02), so it seems correct that the test bridge should
respond with agreement flag set (mask 0x40).