RE: IP SLA and floating default route.

Hello,

I am still concerned about what to monitor from R1 and from R4.

If I do the following:
from R1 I monitor ip address of f0 on R2
from R4 I monitor ip address of f1 on R2

then what happens if f0 on R2 goes down?

R1 will switch it's default route to R3
R4 will still point it's default route to R2 as nothing has changed from
it's side.

Routing between R1 and R4 is broken now.

 
          ---(f0)R2(f1)---
          | |
R1(f0)----| |----(f1)R4
          | |
          ---(f0)R3(f1)---

-----Original Message-----
From: Sonu Khandelwal (sokhande) [mailto:sokhande_at_cisco.com]
Sent: 5-Jul-10 02:12
To: Jack Router; Cisco certification
Subject: RE: IP SLA and floating default route.

Hi Jack,
Yes, I meant R4 and not R2.
we are tracking next hop address of R2 (interface address of f0) on R1.
say only f0 goes down at R2 , 10.1.1.2 will not be pingable from R1 and
traffic will switch to R3. Now you should have default route at R3 which
points to R4.

Similarly, you should have one default route at R2 which points to R4.
it will make sure traffic goes to R4 when f0 interface at R2 is up.

Above will solve the traffic moving from R1 to R4.

Now you should have specific routing table for traffic moving from R4 to
R1.

Hope this helps.

Thanks,
Sonu

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Jack Router
Sent: Monday, July 05, 2010 9:04 AM
To: 'Cisco certification'
Subject: RE: IP SLA and floating default route.

Thanks for your answer. You meant R4 (not R2) in your example ?

I think that monitoring from R1 and R4 the facing interface of R2 will
not provide full redundancy. It will work if R2 dies completely but what
if only f0 fails on R2 ? R1 will switch default route to R3, but R4 will
still point to R2.

After some tests I was thinking about monitoring the opposite interface
on R2. From R1 I monitor R2's f1 and from R4 I monitor R2's f0. This may
provide better redundancy but may have a caveat as well, here is an
example:

1. R4 monitors R2 f0.
2. R2 f0 is up
3. Default route points to R2
4. R2's f1 goes down
5. R4 does not see R1's f0 and switches default route to R3.
NOW is the interesting part:
6. R4 sees again R2's f0 via new default route to R3 7. R4 switches
default route back to R2 8. R4 does not see R1's f1 and switches default
route back to R3.

And so on, we have a loop in the process. Steps 4 to 8 fill repeat
forever.
Default route on R4 will be flapping between R2 and R3. I tested this on
my lab.

I am looking for a way to define a TTL on icmp-echo packets send by R4
(so
R4 will not reach R2 f0 via R3) but it looks like there is no such
thing...

Any ideas ?
BTW, this is my own "requirement", not a real example from any workbook.

-----Original Message-----
From: Sonu Khandelwal (sokhande) [mailto:sokhande_at_cisco.com]
Sent: 4-Jul-10 13:04
To: Jack Router; Cisco certification
Subject: RE: IP SLA and floating default route.

Hi Jack,
Let me understand your requirement.

You want a default route at R1 and R4 which point to R2. You have a
default route on R2 which again points to R1. Will it not cause a loop?

Let me assume you want to have a primary Default route at R1 and R4
which points to R2 and backup default route points towards R3 . You can
try something like this:

Configure this on R1:

track 1 ip sla 1 reachability
ip sla 1
 icmp-echo 10.1.1.2
ip route 0.0.0.0 0.0.0.0 10.1.1.2 track 1 ip route 0.0.0.0 0.0.0.0
10.1.1.3 30 (if you want backup route which goes towards R3).

onfigure this on R2:

track 1 ip sla 1 reachability
ip sla 1
 icmp-echo 20.1.1.2
ip route 0.0.0.0 0.0.0.0 20.1.1.2 track 1 ip route 0.0.0.0 0.0.0.0
20.1.1.3 30 (if you want backup route which goes towards R3).

I am assuming R2's interface ip is 20.1.1.2 and R3's interface ip is
20.1.1.3.

Thanks,
Sonu

-----Original Message-----
From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
Jack Router
Sent: Sunday, July 04, 2010 8:10 PM
To: 'Cisco certification'
Subject: IP SLA and floating default route.

Hello experts,

I am trying to implement floating default routes on R1 and R4 using ip
sla and track:

Primary default route should go via R2.
R2 and R3 have default route to R1

Here is the diagram:

10.1.1.0/24 20.2.2.0/24

          ---(f0)R2(f1)---
          | |
R1(f0)----| |----(f0)R4
          | |
          ---(f0)R3(f1)---

The question is:
what should I monitor on R4 ?

Thanks,

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Received on Mon Jul 05 2010 - 10:07:48 ART