IP SLA feature

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Nov 13th, 2008
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I have 1841 router and have two ISP for backup, when i tried to configure IP SLA feature for redundancy i found that i have not enough DRAM and flash to run the IOS which support IP SLA, currently i have DRAM 128MB and flash 32MB, is there any other way to achieve redundancy without IP SLA.


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Joseph W. Doherty Thu, 11/13/2008 - 05:33
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Assuming your ISP connections are Ethernet, two other solutions that come to mind but both require ISP cooperation. One would be to run an active routing protocol with your ISPs, the other, use a GRE tunnel and keepalives, with your ISPs.

itdsmartnet Thu, 11/13/2008 - 05:49
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what will the step by step configuration for GRE tunnel.


Joseph W. Doherty Thu, 11/13/2008 - 06:11
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Something like:

config terminal

interface tunnel 1

ip address x.x.x.x y.y.y.y

tunnel source x.x.x.x

tunnel destination x.x.x.x


ip tcp adjust-mss xxxx


The tunnel address can be defined for point-to-point.

Tunnel source address could be you existing serial IP address.

Tunnel destination address could be other side's existing serial IP address.

Keepalive is key component to take tunnel down if it doesn't see other side.

Optionally, you can adjust MSS to allow for GRE overhead.

More information on any of the above can be found if you search Cisco's web site.


Also, you need to direct you traffic to use the tunnel vs. the existing link.

Also, when I note using serial addresses, in your case, tunnel source.destination addresses would be addresses between you and ISP which may be Ethernet.


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