From: Enrico Asproni (easproni@cisco.com)
Date: Sun Nov 09 2003 - 07:53:41 GMT-3
Alec,
Determining if this is a good choice really depends on what you are
asked to do. If your requirement tells you that the bri needs to come
up if the physical between R1 and the FR switch goes physically down
then using the backup interface will do the job nicely. But you will
definitively loose connection with R3 though (unless in your topology
R2 and R3 are somehow interconnected via some other interfaces ..)
Still looking at your topology, the backup interface on R1 will not
come up if R2 looses its connectivity to the FR switch. If this is
the case, the pvc on R1 will look like (assuming se0/0.123 is your
multipoint subinterface and 102 the local dlci for your R1-R2 link) :
R1#sh frame map
Serial0/0.123 (up): ip 172.31.100.2 dlci 102(0x25C,0x94C0), static,
broadcast,
CISCO, status defined, inactive <---
As you see, in this last case the serial0/0.123 remains clearly UP
and no backup call is triggered.
The following condition on R1's serial0/0.123 would cause the backup
to come up (physical break in the link between R1 and FR switch or
"shutdown" on the interface of FR switch to which R1 connects) :
R1#sh frame map
Serial0/0.123 (down): ip 172.31.100.2 dlci 102(0x25C,0x94C0), static,
broadcast,
CISCO, status deleted
The serial link here is clearly down, this is the condition to trigger
the backup call. Note : (administratively down) on this same interface
will NOT be a valid condition to trigger the backup call.
Cheers,
Enrico
"Pun, Alec CL" wrote:
>
> Thanks enrico,
>
> That means using an ISDN to backup a multipoint serial is not a good choice
> ?
>
> Referring to the posted topology, I am just afraid even if serial link on R2
> breaks, R1 will not kick up the ISDN because the PVC to R3 is UP and so as
> the physical interface. Therefore, I really doubt whether implementing
> backup in this case is a wise choice.
>
> regards,
> alec
>
> -----Original Message-----
> From: Enrico Asproni [mailto:easproni@cisco.com]
> Sent: Sunday, November 09, 2003 5:54 PM
> To: Pun, Alec CL
> Cc: ccielab@groupstudy.com
> Subject: Re: Using backup interface to backup multipoint serial
> interface
>
> Alec,
>
> You have to consider the F.R. switch on this scenario. The backup
> interface will come up only if the physical link between R1 and
> the frame-relay switch goes physically down. One way to simulate
> this is to access the frame-relay switch (if you can) and shutdown
> the interface to which R1 connects (shut/no shut on R1's serial
> will not work). Obviously doing so will also kill your PVC to R3.
>
> In other words, the backup interface will only come up if R1 looses
> connectivity to the FR switch, and since in your case R1 uses a
> multipoint subinterface, if this link goes down, so will your PVC
> to R3...
>
> HTH,
>
> Enrico
>
> "Pun, Alec CL" wrote:
> >
> > I just read a sample configuration to use backup interface to backup
> > multipoint serial interface.
> > R1 serial interface is a multipoint interface having DLCI to R2 & R3. My
> > question is if I use backup interface bri0 on the serial interface of R1
> > only, in case R2 is down, R1 may not kick up the ISDN connection 'coz the
> > PVC to R3 is still UP and that makes the serial interface remains UP too.
> > Please correct if I made any wrong assumtions.
> >
> > thanks
> > alec
> >
> > R1 ----- ISDN ----- R2
> > | |
> > |---------FR -----------|
> > |
> > |
> > R3
> >
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