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Webcast-Catalyst9k
New Member

Configuring a 1921 router with T1 interface and 4G eHWIC LTE V as failover.

Hi again!

 

Anyone have an idea of how to configure a 1921 router with a serial T1 interface and eHWIC 4G LTE V as a failover?  Below is a portion of the current config with just the serial T1 interface set up.  I have read through the documentation for Cisco but they only mention a failover for a DSL line.  I'm not sure if I can use the same idea for a T1 interface or any other type of interface other than DSL.

 

!
!
!
!
interface GigabitEthernet0/0
 ip address A.x.x.241 255.255.255.248
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 duplex auto
 speed auto
!
interface GigabitEthernet0/1
 no ip address
 no ip redirects
 no ip unreachables
 no ip proxy-arp
!
interface Serial0/0/0
 ip address A.x.x.42 255.255.255.252
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 encapsulation ppp
 no fair-queue
 no cdp enable
!
ip forward-protocol nd
!
no ip http server
no ip http secure-server
!
ip route 0.0.0.0 0.0.0.0 A.x.x.41

 

 

 

3 REPLIES
Hall of Fame Super Gold

There are several approaches

There are several approaches which could work to achieve failover. I think that the most simple one would be to configure a floating static default route pointing to the 4G next hop (a floating static is a static route which includes an administrative distance and might look something like 0.0.0.0 0.0.0.0 B.B.B.B 250).

 

HTH

 

Rick

New Member

Hi Danny,As Rick mentioned

Hi Danny,

As Rick mentioned you can use a floating route.  One issue you would need to watch out for is if the carrier (ISP) had a logical outage that did not bring the T1 interface to a DOWN state.  If that happens the higher metric route would not kick in.

Below is an outline of a dynamic fail-over fail-back for the default route config using boolean and SLA tracking.  Basically the three SLA's will ping a tracking object every 10sec, if the tracked object does not respond that SLA will go to a down state.  The reason for having three and using boolean is for redundancy.  If SLA 100, 4.2.2.2 (a DNS server), goes down but SLA 200 (Google) and SLA 300 OpenDNS are still up then do nothing because the link is still up and the issue may be with that one tracked object.  If all three SLA's go to a down state, TRACK 500 considers the link to be logically unavailable and your floating route then is injected.  Once the tracked object/s come one-line again the default route will fail back to your main default route.  This design will cover physical and logical outages on the ISP side.

Note: It is important to have your static routes in place for the SLA/s, if you do not the SLA/Tracking mechanism will not function correctly since once the fail-over happens the SLA's would go to an UP state and want to fail back bla bla bla

Note2: Once your core is in place you could layer on WAN ACL's, Inspection et certera.  Of course you can modify this example in may ways i.e. more/less SLAs, different tracking objects, using DNS verses ICMP but generally the below has worked well for me in many designs.
 

ip sla 200
icmp-echo 4.2.2.2 source-interface <LAN INTERFACE>
tag PerfMon/TRACKING 4.2.2.2
threshold 1500
timeout 1500
frequency 10
ip sla schedule 200 life forever start-time now

ip sla 300
icmp-echo 8.8.8.8 source-interface <LAN INTERFACE>
tag TRACKING 8.8.8.8
threshold 1500
timeout 1500
 frequency 10
ip sla schedule 300  life forever start-time now

ip sla 400
icmp-echo 208.67.222.222 source-interface <LAN INTERFACE>
tag TRACKING 208.67.222.222
threshold 1500
timeout 1500
frequency 10
ip sla schedule 400 life forever start-time now

track 200 ip sla 200
 delay down 60 up 60
!
track 300 ip sla 300
 delay down 60 up 60
!
track 400 ip sla 400
 delay down 60 up 60
!
track 500 list boolean or
object 200
object 300
object 400
 

ip route 0.0.0.0 0.0.0.0 <primary T1 gateway> track 500
ip route 0.0.0.0 0.0.0.0 <4G LTE Gateway/interface> 250
ip route 4.2.2.2 255.255.255.255 <primary T1 gateway> permanent
ip route 8.8.8.8 255.255.255.255 <primary T1 gateway> permanent
ip route 208.67.222.222 255.255.255.255 <primary T1 gateway> permanent

 

show track xxx is good to check the status of the tracking/sla

Hope this help

Cheers,
Merlin

 

 

New Member

Hi Danny,As Rick mentioned

.

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