Commit 0c03150e authored Jul 22, 2011 by stephen hemminger Committed by David S. Miller Jul 22, 2011

bridge: send proper message_age in config BPDU

A bridge topology with three systems:

      +------+  +------+
      | A(2) |--| B(1) |
      +------+  +------+
           \    /
          +------+
          | C(3) |
          +------+

What is supposed to happen:
 * bridge with the lowest ID is elected root (for example: B)
 * C detects that A->C is higher cost path and puts in blocking state

What happens. Bridge with lowest id (B) is elected correctly as
root and things start out fine initially. But then config BPDU
doesn't get transmitted from A -> C. Because of that
the link from A-C is transistioned to the forwarding state.

The root cause of this is that the configuration messages
is generated with bogus message age, and dropped before
sending.

In the standardmessage_age is supposed to be:
  the time since the generation of the Configuration BPDU by
  the Root that instigated the generation of this Configuration BPDU.

Reimplement this by recording the timestamp (age + jiffies) when
recording config information. The old code incorrectly used the time
elapsed on the ageing timer which was incorrect.

See also:
  https://bugzilla.vyatta.com/show_bug.cgi?id=7164



Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 781223a1

net/bridge/br_private.h

+1 −0

Original line number	Diff line number	Diff line
		@@ -124,6 +124,7 @@ struct net_bridge_port
		bridge_id designated_bridge;
		u32 path_cost;
		u32 designated_cost;
		unsigned long designated_age;

		struct timer_list forward_delay_timer;
		struct timer_list hold_timer;

net/bridge/br_stp.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -164,8 +164,7 @@ void br_transmit_config(struct net_bridge_port *p)
		else {
		struct net_bridge_port *root
		= br_get_port(br, br->root_port);
		bpdu.message_age = br->max_age
		- (root->message_age_timer.expires - jiffies)
		bpdu.message_age = (jiffies - root->designated_age)
		+ MESSAGE_AGE_INCR;
		}
		bpdu.max_age = br->max_age;
		@@ -189,6 +188,7 @@ static inline void br_record_config_information(struct net_bridge_port *p,
		p->designated_cost = bpdu->root_path_cost;
		p->designated_bridge = bpdu->bridge_id;
		p->designated_port = bpdu->port_id;
		p->designated_age = jiffies + bpdu->message_age;

		mod_timer(&p->message_age_timer, jiffies
		+ (p->br->max_age - bpdu->message_age));

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