Tuesday, December 23, 2008

Static Route Issue over Frame-Relay Cloud


While preparing for my CCIE Lab exam I learned a handy IP SLA trick which can be used with static routes/ HSRP/Metro Ethernet for failure detection and to maintain redundancy.

For example Say Router R1 is connected to router R2 via serial point to point link and as well as through frame relay cloud. Now my requirement is to establish connectivity between both router's end subnets using static route only and I am not allowed to use any dynamic routing protocol. My primary path from R1 to R2 should be through Frame Relay Cloud and if FR connectivity goes down between either R1 and Frame Relay cloud or R2 and Frame relay cloud; in that case back to back serial link should be used as backup path otherwise if FR connectivity is up in that situation back to back serial link should not be used.


Things looks easier to achieve at first look...but it's not that easy :-(

Lets talk about how we can fix this and what could be the issues with static routing.

1.) We can use Floating static route for back to back serial link....right :-)....Nooooo

Why ?

Because if we use floating static route ...the problem will be if say connectivity between R2 and FR cloud goes down ....In that case connectivity between FR cloud and R1 will still remain up so primary static route will stay in routing table and float static route will never get installed in routing table of R1.


2.) I thought we can fix it with frame relay end to end keep alive tool...but this feature can only be used with FR subinterfaces (like point to point subinterface or multipoint subinterface) ; but in this sceanrio say examiner asked us to not to use FR subinterfaces and we have to use FR physical interfaces.

.......oops .....then what we can do to solve this now....looks like we all road closed :-(

hmmmmm...take a deep breath ......we still have 2 ways to fix this. :-)

1.) Use ip sla track
2.) Use GRE tunnel


Here I'll show my personal preference...the 1st method :-)

I have attached the topology diagram/ router configurations with solution. Incase still you face issue then drop me an email at deepakarora.1984@gmail.com


Best Regards,
Deepak Arora


Configuration

<-------------------------------------------------------->
R1
<-------------------------------------------------------->
ip sla monitor 1
type echo protocol ipIcmpEcho 1.1.1.2
timeout 500
frequency 3
ip sla monitor schedule 1 life forever start-time now
--------------------------------------------------------

track 1 rtr 1
!
--------------------------------------------------------

interface Serial1/0
ip address 1.1.1.1 255.255.255.252
encapsulation frame-relay
serial restart-delay 0
frame-relay map ip 1.1.1.2 102 broadcast
no frame-relay inverse-arp
!
interface Serial1/1
ip address 2.2.2.1 255.255.255.252
serial restart-delay 0
!
interface FastEthernet2/0
ip address 10.0.0.1 255.0.0.0
duplex auto
speed auto

----------------------------------------------------------

ip route 20.0.0.0 255.0.0.0 1.1.1.2 track 1
ip route 20.0.0.0 255.0.0.0 2.2.2.2 10
-----------------------------------------------------------

<---------------------------------------------------------------------->

<------------------------------------------->
R2
<------------------------------------------->

interface Serial1/0
ip address 1.1.1.2 255.255.255.252
encapsulation frame-relay
serial restart-delay 0
frame-relay map ip 1.1.1.1 201 broadcast
no frame-relay inverse-arp
!
interface Serial1/1
ip address 2.2.2.2 255.255.255.252
serial restart-delay 0
!
duplex auto
speed auto
!
interface FastEthernet2/0
ip address 20.0.0.1 255.0.0.0
duplex auto
speed auto
!
---------------------------------------------

ip route 10.0.0.0 255.0.0.0 2.2.2.1
ip route 10.0.0.0 255.0.0.0 1.1.1.1
!

----------------------------------------------


<-------------------------------------------------------------------->

<---------------------------------------->
R3
<---------------------------------------->

no ip routing

----------------------------------------

interface FastEthernet0/0
ip address 10.0.0.2 255.0.0.0
no ip route-cache
duplex auto
speed auto
!

-----------------------------------------
ip default-gateway 10.0.0.1

-----------------------------------------


<---------------------------------------------------------->

<------------------------------------->
R4
<------------------------------------->

no ip routing

-------------------------------------


!
interface FastEthernet0/0
ip address 20.0.0.2 255.0.0.0
no ip route-cache
duplex auto
speed auto
!

--------------------------------------

ip default-gateway 20.0.0.1
!
--------------------------------------

1 comment:

Sandy Shaw said...

Nice Article! Thanks for sharing with us.
IP Routing