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IP SLA Cisco 2821

Posted on 2011-03-08
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Last Modified: 2013-12-14
I have a cable modem with static address run to gi0/1 on a Cisco 2821 ios Version 12.4(15)T10. The gi0/1 has dhcp enabled (carrier uses mac to give out address reservation). This is the primary internet carrier. The local lan is on gi0/0, which has another cisco router on it used by another entity that has internet access from another carrier.

I need to have the 2821 direct traffic to that device when the gi0/1 interface can no longer get outbound. i have tried static routes, such as 0.0.0.0 0.0.0.0 gi0/1 and 0.0.0.0 0.0.0.0 otherrouter address 250 but that results in the other router getting all of the traffic. This resuts in a far slower internet, as its a low speed backup T1. I need guidance on making the SLA or whatever is the best fit for this to work.

Thanks
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Question by:nhskitech
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Expert Comment

by:Don Johnston
ID: 35071629
Object tracking with SLA sounds like what you need.

Try this:

http://www.cisco.com/en/US/docs/ios/12_3/12_3x/12_3xe/feature/guide/dbackupx.html

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Author Comment

by:nhskitech
ID: 35071843
The backup router is still getting the traffic when the ip sla is defined. attached is the base code of the router. Can you show the changes necessary in the code?
Using 3956 out of 245752 bytes
!
! Last configuration change at 10:55:52 PCTime Tue Mar 8 2011 by x
! NVRAM config last updated at 10:56:30 PCTime Tue Mar 8 2011 by x
!
version 12.4
service timestamps debug datetime msec
service timestamps log datetime msec
service password-encryption
!
hostname x
!
boot-start-marker
boot-end-marker
!
!
no aaa new-model
clock timezone PCTime -5
clock summer-time PCTime date Apr 6 2003 2:00 Oct 26 2003 2:00
dot11 syslog
!
!
ip cef
!
!
ip domain name x.local
ip multicast-routing
!
multilink bundle-name authenticated
!
!
!
!
!
username privilege 15 password 
archive
 log config
  hidekeys
!
!
!
!
!
!
!
interface Multilink1
 ip address 10.10.10.2 255.255.255.252
 ip pim sparse-dense-mode
 fair-queue 64 16 0
 no cdp enable
 ppp multilink
 ppp multilink group 1
!
interface GigabitEthernet0/0
 description $LAN$
 ip address 172.x.x.x  255.255.255.0
 ip nat inside
 ip virtual-reassembly
 duplex auto
 speed auto
 fair-queue
 no cdp enable
!
interface GigabitEthernet0/1
 description Metrocast
 ip address dhcp
 ip access-group 152 in
 ip flow ingress
 ip flow egress
 ip nat outside
 ip virtual-reassembly
 duplex auto
 speed auto
 no cdp enable
!
interface Serial0/0/0
 no ip address
 encapsulation ppp
 fair-queue
 ppp multilink
 ppp multilink group 1
!
interface Serial0/1/0
 no ip address
 encapsulation ppp
 fair-queue
 ppp multilink
 ppp multilink group 1
!
ip forward-protocol nd
ip route 10.0.0.0 255.0.0.0 172.x.x.x
ip route 172.x.x.0 255.255.255.0 172.x.x.x 
ip route 172.x.x.0 255.255.255.0 10.10.10.1
ip route 172.x.x.0 255.255.255.0 172.x.x.x 
ip route 172.x.x.0 255.255.255.0 172.x.x.x 
ip route 192.x.x.0 255.255.255.0 172.x.x.x 
!
ip flow-export version 5
ip flow-export destination 172.x.x.x 2055
!
ip http server
ip http authentication local
no ip http secure-server
ip nat pool name 216.x.x.x 216.x.x.x netmask 255.255.255.252
ip nat inside source list 151 interface GigabitEthernet0/1 overload
!
access-list 150 deny   tcp host 172.x.x.x any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 deny   tcp host 172.x.x.x  any eq www
access-list 150 permit ip any any
access-list 151 permit ip host 172.x.x.x  any
access-list 151 permit ip host 172.x.x.x  any
access-list 151 permit ip host 172.x.x.x  any
access-list 151 permit tcp any any
access-list 152 deny   icmp any any echo
access-list 152 deny   icmp any any echo-reply
access-list 152 deny   udp any any gt 32768
access-list 152 permit ip any any
snmp-server community name RW
!
!
!
!
control-plane
!
banner login ^C
*****************************************************************************
*                     				                            *
*                                                                           *
*                                                  		            *
*                                                                           *
*                                     					    *
*****************************************************************************
^C
!
line con 0
 login local
line aux 0
 login local
line vty 0 4
 login local
 transport input ssh
!
scheduler allocate 20000 1000
ntp clock-period 17180135
ntp server 172.x.x.x
!
end

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LVL 50

Expert Comment

by:Don Johnston
ID: 35073271
>The backup router is still getting the traffic when the ip sla is defined.

Please post the config that you tried but wouldn't work.
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Expert Comment

by:MAG03
ID: 35081968
which interface is the T1 backup connected to?


you could use HSRP for this: (for the sake of this example I am using g0/2 as the backup.)

ip route 0.0.0.0 0.0.0.0 g0/2 track 6
ip route 0.0.0.0 0.0.0.0 g0/1 track 5

track 5 ip route 0.0.0.0 0.0.0.0 reachability

int g0/1
standby 1 ip 172.16.6.100
standby 1 preempt
standby 1 priority 110 decrement 20
standby 1 track 5

int g0/2
standby 1 ip 172.16.6.100
standby 1 preempt
standby 1 track 6

The priority command on g0/1 will make it the dominent interface until the default route is detected as down. When the default route goes down the priority will be decreased by 20 placing it under the default priority of g0/2 (default priority for HSRP is 100).

to check the configuration you can issue the show standby or show standby brief commands.

g0/1 should be shown in active state and g0/2 should be shown in standby state
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Author Comment

by:nhskitech
ID: 35173680
Thanks for the response MAG, I've been away on business and will attempt this ASAP this week.
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Accepted Solution

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MAG03 earned 500 total points
ID: 35364124
I feel that HSRP is the better choice here. The SLA will work if you know the destination IP ( in this case most likely the ISP's IP) that connects to your router, But with HSRP you can track the default route and can save some time finding what IP to track.
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