Hello,
I'm using rstpd application over two switches and they are connected
to another Nortel switch which operates STP rather than RSTP. They are
all connected by a 10/100 ethernet switch which does not process
BPDUs. Here is a simplified diagram when the system is up and running.
+-------------+ R
| Root-Bridge o--------+
+-------------+ STP |
|
+-----------o--------------+
| STP_SW_NORTEL |
+-----------o--------------+
|
L | STP
|
+-----o-----+
+------+ | | 10/100 ethernet
| Host o---------o | switch
+------+ | | (no BPDU processing)
+--o-----o--+
| |
STP | | STP
+----------+ +----------+
p0 | | p0
+-----o-----+ +-----o-----+
| | p1 p1 | |
| RSTP_SW1 o---------------o RSTP_SW2 |
| | RSTP | |
+-----------+ +-----------+
The MACs of the bridges and the root bridge to which they are all
synced with are:
Root bridge: 00:11:22:xx:xx:xx
STP_SW_NORTEL: 00:11:58:xx:xx:xx
RSTP_SW1: 02:e0:xx:xx:44:01
RSTP_SW2: 02:e0:xx:xx:42:01
The STP_SW_NORTEL carries the root bridge identifier in its STP BPDU
and the RSTP algorithm on RSTP_SW1 and RSTP_SW2 migrates the p0 port
to perform STP transactions. After a brief TopologyChange transaction,
the port states were as follows:
Switch Port Root-Bridge Designated-Bridge Role/State
RSTP_SW1 p0 00:11:22:xx:xx:xx 02:e0:xx:xx:44:01 Root,Fwd
p1 00:11:22:xx:xx:xx 02:e0:xx:xx:44:01 Altn,Disc
RSTP_SW2 p0 00:11:22:xx:xx:xx 02:e0:xx:xx:42:01 Root,Fwd
p1 00:11:22:xx:xx:xx 02:e0:xx:xx:42:01 Desg,Fwd
p0 - auto-p2p, non-edge
p1 - auto-p2p, auto-edge
The cost and port/bridge priorities are not modified and are left to
defaults assigned by the rstpd application. Sniffing the BPDUs from
the host reveals that after a while only STP_SW_NORTEL switch is
sending out the hello packets, and the bridges RSTP_SW1 and RSTP_SW2
are in sync with it.
I'm facing the following problem:
If the link L is removed, the switch RSTP_SW1 and RSTP_SW2 ends up
forming a loop. The port RSTP_SW1::p1 comes to forwarding state before
blocking the port RSTP_SW1::p0. The following are the sequence of
ports states:
RSTP_SW1 RSTP_SW2
[before L is connected]
p0: altn/disc desg/fwd
p1: root/fwd desg/fwd
[after L is connected]
p0: root/fwd root/fwd
p1: altn/disc desg/fwd
[after L is disconnected]
p0: desg/fwd root/fwd
p1: root/disc desg/fwd
p0: desg/fwd root/fwd
p1: root/learn desg/fwd
p0: desg/fwd root/fwd
p1: root/fwd desg/fwd
After disconnecting link L, the RSTP port moves through the
learning/forwarding states that puts the bridge to loop.
If the mediating ethernet switch is removed and if the switches
RSTP_SW1 and RSTP_SW2 are directly connected to STP_SW_NORTEL switch,
the switches RSTP_SW1 and RSTP_SW2 loops up, if the root bridge link,
R is removed. The sequence seems to be:
1. RSTP_SW2::p0 sends out a TC BPDU with its own bridge ID as
root bridge id.
2. RSTP_SW1::p0 sends out a TC BPDU with the root bridge as
the lost root bridge's ID.
3. The above when received by RSTP_SW2::p0, thinks that it has
received a superior bridge and tries to sync up with the root bridge
ID sent by its neighbour: RSTP_SW1.
After the above sequence, the port RSTP_SW1::p1 ends up in
learning/forwarding sequence which eventually forms a loop before
migrating any of the other STP ports to blocking/discarding mode.
It would be of great help if some one could provide an insight into
what could be going wrong.
Regards,
Ramasamy
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