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RE: Interesting DDR Scenario posted 02/23/2002
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How about "dialer priority 0-255".

-----Original Message-----
From: Wade Edwards [mailto:wade.edwards@xxxxxxxxxxxxxxxxxxx]
Sent: Friday, February 22, 2002 6:19 PM
To: John Neiberger
Cc: ccielab@xxxxxxxxxxxxxx
Subject: RE: Interesting DDR Scenario

You would need to set the fast-idle on the lower priority dialer
interface to something low like 1 second.  That way when there is
contention for the line the lower priority dialer will get disconnected
after 1 second of inactivity and the higher priority line will be able
to call.

You might want to set the fast-idle on the higher priority dialer
interface to something high so it will not be easily preempted by the
lower priority dialer interface.


 -----Original Message-----
From: 	John Neiberger [mailto:neiby@xxxxxxxxxx] 
Sent:	Friday, February 22, 2002 4:44 PM
To:	ccielab@xxxxxxxxxxxxxx
Subject:	Interesting DDR Scenario

I posted this on the regular list but since I haven't figured 
out the solution yet I thought I'd post it here, as well.  To 
summarize what you're about to read, I need to figure out how 
to give one Dialer interface priority over another when 
accessing the same BRI.  So, if Dialer0 (low priority) has 
placed a call, if Dialer1 (high priority) then needs to place a 
call, I want Dialer1 to preempt Dialer0 and take over the BRI.  
Here's the full post:


I was just talking to a guy I work with about this and I 
thought it was an interesting scenario.  It was his idea and my 
first thought was that it wasn't possible, but then after a 
little more pondering I decided that it might be possible.  
Note:  'possible' does not mean desirable.  :-)    Here's the 

  |  \        
  |    \
  |      \
  |        \
  |          \
  |            \
  |              \
[C] ----------- [D]

Site A is connected to B, a disaster recovery facility, via 
frame relay.  A also has point-to-point connections to sites C 
and D.   C and D are connected via frame relay but obviously 
only use the frame relay link to reach A if their own primary 
link goes down.

C and D have ISDN connections configured to dial B in case both 
links to A go away (Dialer Watch).  Now for the twist....  What 
if you wanted to configure C to dial D when the load on its 
primary link reached a certain point, yet still dial B if both 
point-to-point links went down?

I haven't completely figured out how to do this yet, but here's 
a start.  You might configure two Dialer profiles, one for each 
destination.  On the major interface on C you'd configure 
Dialer0 as your backup interface and configure an appropriate 
load.  When the line utilization reaches that load, the router 
would dial Site D.

Then you might configure Dialer Watch on Dialer1 and make it 
dialer Site B if routes originating from Site A disappear.  The 
difficulty is that the Dialer interface that calls Site B would 
have to have absolute priority.  If the primary link goes down, 
because Dialer0 is configured as a backup it might grab the BRI 
first.  Even if it does get there first, when Dialer Watch 
kicks in, we'd have to have a way to clear the line immediately 
so Dialer1 could dial out.

Is that possible?  Admittedly, I'm a bit weak on DDR of this 
variety, but this sounded like an interesting brain teaser.


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