Re: IP SLA and floating default route.

Jack,

Your requirements are very hard to understand. It might help if you
provide some clarification on what each router's role is...

IE. No IGP is currently running, only static routing. R1 has a default
route to the Internet. R2 has a static default route to R1. R3 has a
static default route to R1.
How can you implement static floating routes on R4 to get to the Internet
with the preference of going through R2. Is this correct?

If so, then you need to add multiple floating routes with varying AD. The
first SLA is to get the verify the first leg of the link and force the
route:

On R4
ip route 10.1.1.0 255.255.255.0 20.2.2.3 50
ip route 10.1.1.0 255.255.255.0 20.2.2.2 track 1
ip route 0.0.0.0 0.0.0.0 20.2.2.3 50
ip route 0.0.0.0 0.0.0.0 20.2.2.2 track 2

track 1 ip sla 1 reachability
ip sla 1
icmp-echo 20.2.2.2

track 2 ip sla 2 reachability
ip sla 2
icmp-echo 10.1.1.1

Now you also have to be able to get traffic back from R1 to R4
on R1:
ip route 20.2.2.0 255.255.255.0 10.1.1.3 50
ip route 20.2.2.0 255.255.255.0 10.1.1.2 track 1
ip route <Subnet & Mask hanging off of R4> 10.1.1.3 50
ip route <Subnet & Mask hanging off of R4> 10.1.1.2 track 2

track 1 ip sla 1 reachability
ip sla 1
icmp-echo 10.1.1.2

track 2 ip sla 2 reachability
ip sla 2
icmp-echo 20.2.2.4

Does this make sense?
On Mon, Jul 5, 2010 at 9:07 AM, Jack Router <pan.router_at_gmail.com> wrote:

> 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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>
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Received on Tue Jul 06 2010 - 13:06:16 ART