From: ccie2be (ccie2be@nyc.rr.com)
Date: Thu Sep 25 2003 - 15:20:02 GMT-3
Hi Ken,
Thanks for the clarification. However, now you've got me wondering about
Dialer Int #. I thought that one of the primary benefits of using a Dialer
Int is that because it's a virtual interface, a physical isdn interface
isn't "taken out of commission" by the use of Backup Interface. Am I
mistaken about that?
Also, suppose you have a scenario where there's interesting traffic defined
directly on the physical isdn interface and you have a Dialer Interface used
as a Backup Interface which uses the same physical isdn interface. What
happens when interesting traffic brings up the phy isdn interface and uses
one channel and then the primary link fails. Would the Dialer interface
consider the phy isdn interface unavailable or would it just use the other B
channel or would the fast idle-timeout kick in or something else I didn't
think of happen?
Thanks, dt
----- Original Message -----
From: "Kenneth Wygand" <KWygand@customonline.com>
To: "ccie2be" <ccie2be@nyc.rr.com>; "Group Study" <ccielab@groupstudy.com>;
"Jonathan V Hays" <jhays@jtan.com>
Sent: Thursday, September 25, 2003 12:06 PM
Subject: RE: Should I disable cdp on ISDN
Everything you said is correct except for two things:
1) Backup interface will not initiate any call. When a link is
configured to use a dialer interface or BRI interface as a backup link,
it brings that link DOWN at layer 2. All attempts to bring the link up
(such as interesting traffic) try to bring the link up at layer 3 and
fail while the primary line is up because layer-2 has been yanked down
by Backup Interface. Do a "debug dialer" and watch the interesting
traffic try to bring the link up and fail if backup interface is holding
it down. However, when the primary line goes down and it "fails over"
to the backup interface, it simply brings the dialer or BRI line back up
at layer 2 - IT DOES NOT INITIATE THE CALL - this is very important - it
STILL requires some other mechanism to provide interesting traffic to
bring the link up.
2) After the link is up, the idle-timeout counts down and is reset to
its configured time every time it sees an interesting piece of traffic
cross the link. When it expires, the link is gracefully torn down at
layer 3 (unlike backup interface which operates at layer 2). The only
exception is dialer watch, which will allow the idle-timeout to count
all the way down to zero (of course, resetting every time it sees
interesting traffic)... once the idle-timeout hits zero, dialer watch
checks to see if the route you are watching is available through any
interface other than the interface dialer-watch has been configured on
itself. If the route is not available through any other interfaces,
dialer watch will reset the idle timeout to the initial value and start
the countdown once again.
If anything is unclear, please let me know and I'll do my best to
explain further.
Kenneth E. Wygand
Systems Engineer, Project Services
CISSP #37102, CCNP, CCDP, MCP 2000, CNA 5.1, Network+, A+
Custom Computer Specialists, Inc.
"It's not just about ending up where you want to be, it's about making
the most of the trip there."
-Anonymous
-----Original Message-----
From: ccie2be [mailto:ccie2be@nyc.rr.com]
Sent: Thursday, September 25, 2003 11:45 AM
To: Group Study; Jonathan V Hays
Subject: Re: Should I disable cdp on ISDN
Hi all,
While I can't claim to be 100% positive about what I'm about to say, I
think
my previous statements remain correct. To reiterate, there are 2
issues a)
what trigger call and b) what traffic transits the link once it's UP.
With Backup Interface, the primary interface going down triggers call.
With Dialer Watch, the the absense of a watched route triggers call.
With OSPF Demand Circuit, the initial sync of the link state db and
subsequent changes to link state db triggers call.
With interesting traffic defined, the interesting traffic triggers call.
As far as I know, it seems that with the exception of Backup Interface,
these triggering methods aren't mutually exclusive, so it's possible,
for
example, to have both OSPF Demand Circuit and Interesting traffic both
in
effect and both trigger calls. In other words, when both features are
in
effect, either OSPF Demand Circuit or Interesting traffic can trigger a
call.
The 2nd issue - what traffic transits an isdn link when it's up - is
independent of what triggers the call. The way I understand it, once
the
link is up any traffic that should transit the link will transit the
link.
So, if you don't want CDP traffic to cross the link when it's UP,
disable
CDP on that interface, regardless of what caused the link to come up in
the
first place.
Another issue to keep in mind, is what causes the isdn link to go down
and
when should the link come down. "Normally", the absense of interesting
traffic for the dialer idle-timeout period. But, I believe there are
other
factors that may have a role in how this issue is handled.
HTH, dt
----- Original Message -----
From: "Jonathan V Hays" <jhays@jtan.com>
To: "'Nawaz, Ajaz'" <Ajaz.Nawaz@bskyb.com>; "'Donny MATEO'"
<donny.mateo@sg.ca-indosuez.com>; "'Peng Zheng'" <zpnist@yahoo.com>
Cc: <ccielab@groupstudy.com>; <nobody@groupstudy.com>
Sent: Thursday, September 25, 2003 9:31 AM
Subject: RE: Should I disable cdp on ISDN
> Now you've got my curiosity up. Exactly how does CDP interact with an
> OSPF demand circuit?
>
> I'm not trying to criticize or flame here - I am ignorant and would
like
> to know. A preliminary search of the Doc CD does not have any
> information tying CDP to OSPF.
>
> Please help,
>
> Jonathan
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Nawaz, Ajaz
> Sent: Thursday, September 25, 2003 8:58 AM
> To: 'Donny MATEO'; Peng Zheng
> Cc: ccielab@groupstudy.com; nobody@groupstudy.com
> Subject: RE: Should I disable cdp on ISDN
>
>
> as a reader this is the most complete reply.
> as I understand it, OPSF demand circuit is the only time where you
would
> explicity disable cdp (interface only) in order to prevent an isdn
> circuit
> from coming UP unecessarily.
>
> ajaz
>
> -----Original Message-----
> From: Donny MATEO [mailto:donny.mateo@sg.ca-indosuez.com]
> Sent: 25 September 2003 08:57
> To: Peng Zheng
> Cc: ccielab@groupstudy.com; nobody@groupstudy.com
> Subject: Re: Should I disable cdp on ISDN
>
>
> What techology are you refering to ? It really is technology specific
>
> backup interface => no need
> static route => make sure you didn't define CDP as interesting traffic
> in
> the dialer-list (there is no need to turn it off)
> ospf demand-circuit => filter it out or turn it off
> dialer-watch=> no need i believe..not sure though..
>
> so which one is it are you refering to ?
>
> Donny
>
>
>
>
>
>
> Peng Zheng <zpnist@yahoo.com>
> Sent by: nobody@groupstudy.com
> 09/25/2003 03:24 PM
> Please respond to Peng Zheng
>
>
> To: ccielab@groupstudy.com
> cc: (bcc: Donny MATEO/ADPC/ASIA/BANQUE_INDOSUEZ/FR)
> Subject: Should I disable cdp on ISDN
>
>
> On page 144 CCIE Practical Studies: Security, it said
> cdp triggers the ISDN call and therefore should be
> disabled if it isn't needed.
>
> Is that true? SHould I always disable cdp when
> configure DDR on ISDN?
>
>
>
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