From: Ayman Hamza (ayhamza@cisco.com)
Date: Thu Oct 03 2002 - 10:59:57 GMT-3
Giuseppe ;
Here how it goes with these two timers.
Once I got an "first" explorer reply from the remote peer that has the resource
I'm looking for , or I got the explorer reply from the lowest cost peer ,
both timers will start. The verify-timer won't be resarted as you have guessed
correctly. The Verify timer will still counting till its end - let's say
the default 4 minutes - and then the entry will be marked stale .
The verify timer will "ONLY" be refreshed once I got another "Test"(or explorer request frame ) from an end station , and AFTER this timer has been reached
its expiry and the entry is marked stale.
To clarifyl:
---ethernet---R1-----------TCP/IP cloud-----------R2-----ethernet---Mainframe
Station behind R1 sends a test frame, R1 doesn't have a cache entry for
the main frame. It sends explorer request to ALL its DLSw known UP peers, and
waits the period defined in explorer-wait-time . R2 says responded first with
the first explorer response, so the MAC address of the main frame is cahced
and the timers "sna-verify-interval", and the "sna-cache-timeout" BOTH
STARTING.
If R1 got a test frame from another end station for the main frame MAC, I won't
ofcourse pass any explorer frames, and R1 will send a reply to teh sation
directly, BUT STILL THE " SNA-VERIFY-INTERVAL" decrements !! also
"SNA-CACHE- TIMEOUT" still decrementing as well.
After the expiry of SNA-VERIFY-INTERVAL timer, then the entry will be marked
stale in the SNA cache , then this timer won't be refreshed till R1 got
another test frame to the same MAC address ofcourse. Note that still
SNA-CACHE-TIMEOUT is still decrementing.
The entry won't be deleted untill the SNA-CACHE-TIMEOUT expired .
If the SNA-CACHE-TIMEOUT is less than SNA-VERIFY-INTERVAL timer, then
SNA-VERIFY-INTERVAL has no effect, as the entry will be deleted before
the entry is marked stale (because SNA-CACHE-TIMEOUT will expire before
SNA-CACHE-TIMEOUT timer) .
Note that:
---------
It could happen that an SNA cache entry can be deleted , even before the expiry
of SNA-CACHE-TIMEOUT, How??!
Here is a scenario:
---ethernet---R1---------TCP/IP cloud-----------R2--TokenRing-----Mainframe
| |
---------------R3---TokenRing------|
If a station sends Explorer frame to R1, and R1 got first response from
R2, then the it will cache an antry with R2. Then this end station will
Send XID , and R1 will send this XID to R2, If token interface of R2 is down
, no XID reply R1 will recieve from R2, then the cached entry will be
deleted, and another cahche entry should be created with R3
as it's another peer(cappable peer in this case).
So a cache entry can be deleted even before SNA-CACHE-TIMEOUT EXPIRY
BECAUSE WE DIDN'T GET THE CORRECT XID response.
(You may ask and how R2 replyed with MAC address of Main frame to R1? this
might happen because the cahed entry didn't marked as stale yet, or the
interface was falpping,...ect )
Hope that helps.
-Ayman
> From nobody@groupstudy.com Wed Oct 2 15:57:00 2002
> Date: Wed, 2 Oct 2002 15:42:27 +0200 (CEST)
> From: =?iso-8859-1?q?giuseppe=20ciferri?= <joscite@yahoo.it>
> Subject: dlsw+ timers and caching
> To: ccielab@groupstudy.com
> MIME-Version: 1.0
> Content-Transfer-Encoding: 7bit
> X-ASK-Info: Confirmed by user
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> Reply-To: =?iso-8859-1?q?giuseppe=20ciferri?= <joscite@yahoo.it>
>
> Hi,
>
> Dlsw+ caching uses 2 principal timer :
> sna-verify and sna-cache-timeout
> After 4 min (verify) router sends a directed CUR to peer(in cache) to verify entry . If any peer do not responds then router delete it from cache.
> But any entry (mac/netbios) is deleted after 16 min (cache-timeout) and router must sends cur to ANY peer for any destination.
> The question is:
> when this timer are reset ?
> probably when there is traffic or this timer never are reset!
> thanks
>
> Giuseppe
>
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> ---------------------------------
> MIo Yahoo! : personalizza Yahoo! come piace a te
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