Subject: Re: [Bridge-mib] Q: dot1dTpAgingTime in RFC1493 ?

From: "Les Bell" <[email-masked]>
Date: Wed, 2 Jan 2002 12:32:18 +0000

Alex,

Ageing can be effectively disabled for specific addresses by making them
permanent, using the dot1dStaticTable (RFC 1493) or dot1qStaticUnicastTable (RFC
2674).

IEEE 802.1D does not allow you to disable the ageing process.  If it is
disabled, you are likely to see traffic mis-directed after a topology change in
a network that implements STP (version 0), resulting in some trafffic being
forwarded to blocked ports.

RSTP does not rely on address ageing, instead it flushes the FDB after a
topology change, so disabling address ageing will have no effect.

Ageing only applies to addresses that have not been active for the period
defined in dot1dTpAgingTime.  The maximum value of 1,000,000 seconds that may be
configured for this is equivalent to more than 11 days.  It is not much of an
overhead to occasionally re-learn addresses that are inactive for such extended
periods.

What benefits do you expect to see if ageing is disabled?

Les...

[email-masked] (Alex Ruzin)@ietf.org on 25/12/2001 10:43:38

Please respond to <[email-masked]>

Sent by:  [email-masked]

To:   <[email-masked]>
cc:
Subject:  [Bridge-mib] Q: dot1dTpAgingTime in RFC1493 ?

Hi,

In RFC1493 there is no option to disable aging process at all.

In our products we have to use one of two *bad* methods:
1. *Edit* the standard MIB to avoid interval "range validity" of
dot1dTpAgingTime:
          dot1dTpAgingTime OBJECT-TYPE
              SYNTAX   INTEGER -- (10..1000000) [the range is commented out]

              ACCESS   read-write
              STATUS   mandatory
              DESCRIPTION
                      "The timeout period in seconds for aging out
                      dynamically learned forwarding information.
                      802.1D-1990 recommends a default of 300 seconds.
                      The value 0 means mode 'aging out is disabled'."
              REFERENCE
                      "IEEE 802.1D-1990: Section 6.7.1.1.3"
              ::= { dot1dTp 2 }

The value '0' of the object means the mode "aging is disabled"

2. Use our *private* MIB for this purpose.

Question: Is WG going to solve this problem in the standard MIB ?
Or: is there another method (may in another MIB) ?
Or: does WG think, that aging process has not to be disabled ?

As example, we propose to add a new special object, something like this:

          dot1dTpAgingEnabled OBJECT-TYPE
              SYNTAX   TruthValue
              ACCESS   read-write
              STATUS   mandatory
              DESCRIPTION
                      "The value true(1) means 'aging mode is enabled'.
                       The value false(2) means 'aging mode is disabled'"
              REFERENCE
                      "IEEE 802.1D-1990: Section 6.7.1.1.3"
              ::= { dot1dTp 5 }

Best regards, Alex

_______________________________________________
Bridge-mib mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/bridge-mib

_______________________________________________
Bridge-mib mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/bridge-mib

---

From: [email-masked] (Alex Ruzin)
Date: Wed, 2 Jan 2002 16:10:29 +0200

On Wednesday, January 02, 2002 2:32 PM Mr. Les Bell wrote:
Les > Ageing can be effectively disabled for specific addresses by
Les > making them
Les > permanent, using the dot1dStaticTable (RFC 1493) or
Les > dot1qStaticUnicastTable (RFC
Les > 2674).

No, this method is not good for us, because we would like to consider
automatically learned entries.

> a network that implements STP (version 0), resulting in some
> traffic being

No, disabled ageing doesn't prevent STP: it disables only "regular ageing"
while
"fast" ageing operates anyway.

> topology change, so disabling address ageing will have no effect.

Yes, in RSTP address ageing will have no effect,
if the value of ForceVersion (17.16.1) for the Bridge is 0, indicating that
the Bridge is operating in
STP Compatibility mode - 17.19.6 & 17.28 in IEEE 802.1y

> What benefits do you expect to see if ageing is disabled?

OK, let us consider the "silent" device, that had been learned with a
regular
learning process and now only receives data a great amount of time (weeks).
The example - some "spy" system. And we don't want to relearn it after
ageing,
because relearning may cause an unwanted from security reasons address
flooding.

The second case - needs of debugging. There disabled ageing and ageing
of 11 days - is not the same.
[Sincerely, for us is a first purpose,
but may be not only for us]

What do you think about it ?

Thank you for the cooperation, Alex
---------------------
Open Source RSTP  https://sourceforge.net/projects/rstplib/
Optical Access Ltd. http://www.opticalaccess.com