How to create failover for default route

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Feb 21st, 2008
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Hi, I want to ask how to configure a failover for a default route (ip route 0.0.0.0 0.0.0.0 <gatewayIP>)


If the default route 222.222.222.222 is not reacheable, how can i automatically put a backup default route of 111.111.111.111? How can it test if the GW 222.222.222.222 is down so that it can put 111.111.111.111 as the GW.


Thanks,

Ninoy

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Danilo Dy Thu, 02/21/2008 - 23:46
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Pre,


With administrative distance. i.e.

ip route 0.0.0.0 0.0.0.0 222.222.222.222

ip route 0.0.0.0 0.0.0.0 111.111.111.111 10


Once 222.222.222.222 is not reachable (shutdown the interface - or unplug the cable), 111.111.111.111 will be the GW.


Regards,

Dandy

ninoy_lim Thu, 02/21/2008 - 23:50
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Hi Dandy,


Thanks for the fast reply, but is there any way that 222.222.222.222 is not reachable on the server side of the network and the router detects that the link is still active, its just if you ping it, it will result to a timeout.


Thanks,

Ninoy

Danilo Dy Fri, 02/22/2008 - 04:29
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Hi,


Who's pinging? The server or the router?


...and what is the link type connected to the router interface for the 222.222.222.222?


Regards,

Dandy

dongdongliu Fri, 02/22/2008 - 00:28
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hi


I do not know what real topology is there, it`s just a suggestion:

if GW 111.111.111.111 & 222.222.222.222 are in the same router, the router have a loopback interface with ip address 3.3.3.3 and have a right route to come back,

so now


ip route 0.0.0.0 0.0.0.0 3.3.3.3

ip route 3.3.3.3 255.255.255.255 111.111.111.111

ip route 3.3.3.3 255.255.255.255 222.222.222.222


regards

dongdong


Goutam Sanyal Fri, 02/22/2008 - 01:01
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Hi,


If I assume that you are using two different interfaces for a single gateway with two deferent bandwidth from two deferent/same ISP, then you can choose the following:


ip route 0.0.0.0 0.0.0.0 Serial0/1/1

ip route 0.0.0.0 0.0.0.0 Serial0/1/0


It'll help you to loadbalance the bandwidth as well as it will work the same if one link goes down.


or you can go as per medan's post (Senior Consultant, NCS Pte. Ltd)


Thanks

Goutam

dongdongliu Fri, 02/22/2008 - 01:29
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hi Goutam


if peer router has a interface Serial 0/0/0 that connect to local interface Serial 0/1/1 , remove ip address from Serial 0/0/0 and remain encapsulation PPP, both side`s serial interface will still display "up up", maybe loadlance between two link is fail.


regards

dongdong

Goutam Sanyal Fri, 02/22/2008 - 02:04
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Hi Dong Dong liu,


I appreciate your point, but please let me know why you are going to withdraw the IP address by remaining the Encapsulation? Any valid reason to doing the same in production network? Where as, at that condition no data will flow.


See, my point of view is that to send the traffic load with the both active interface, as well as with the help of load balancing. Where I'd like to utilize the max through put of the both link at a time if 1 interface goes down then, the remain active interface will also able to carry the traffic very well.


Suggestion is always appreciable.


Thanks

Goutam


dongdongliu Fri, 02/22/2008 - 02:40
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hi Goutam


thanks for sharing your opinion, I agree with your point of view, LB is a good idea.

I just think of local interface act as a GW, if peer interface has "a little" problem and local interface`s states is "up up",so this default route is still a valid route in the local route table, and half of the traffic will still flow that interface. It's a bit of risk.


regards

dongdong

Goutam Sanyal Fri, 02/22/2008 - 04:15
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Hi Dong Dong


Thanks again :)

If I configure my site-office router with the bellow congiguration:


Router-Site-Office#sh ip int brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 x.x.x.x1 YES NVRAM up up

Serial0/1/0 10.10.1.2 YES NVRAM up up

Serial0/1/1 20.20.1.2 YES NVRAM up up

Router-Site-Office#sh run | in ip route

ip route 0.0.0.0 0.0.0.0 Serial0/1/1

ip route 0.0.0.0 0.0.0.0 Serial0/1/0

Router-Site-Office# sh ip route

C10.10.1.1/32 is directly connected, Serial0/1/0

C10.10.1.0/30 is directly connected, Serial0/1/0

C20.20.1.1/32 is directly connected, Serial0/1/1

C20.20.1.0/30 is directly connected, Serial0/1/1

S*0.0.0.0/0 is directly connected, Serial0/1/1

is directly connected, Serial0/1/0


If HO as per bellow:


Route-HO# sh ip route ++

C10.10.1.0/30 is directly connected, Serial0/1/0

C10.10.1.2/32 is directly connected, Serial0/1/0

C20.20.1.0/30 is directly connected, Serial0/1/1

C20.20.1.2/32 is directly connected, Serial0/1/1

S*0.0.0.0/0 is directly connected, Serial0/1/1

is directly connected, Serial0/1/0


++ if no other route is connected with HO router, then go for this option.


As per the above post “how to configure a fail over for a default route?” I think its pretty clear how to do that. The main post is related with the “fail over”, then we can assume that there are more than one link (2 in this case). When 2 links are available, then consider the both links to use with the max utilization. See the basic point is how you are observing the network/ the topology. And as per my knowledge CISCO has given us the facility to play with data as you can. ;)


Thanks

Goutam


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