DUal ISPs on 2811

Unanswered Question
Oct 14th, 2010
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Hello All,



I was wondering if someone could point me in  eright direction.  I have a 2811 router that I want to have you 2 different ISPs.  I would think the easiest way to go would be to have a primary ISP and a secondary one where the traffic flows through the Primary until it goes down then switches over to the secondary automatically and then back to the primary once it is back up.  Can anyone point me in the right direction?  FYI the router's outside interface, and both ISPs will be plugged into the same unmanaged 8 port switch unless it just can't be done line that.



Thanks in advance!

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Jon Marshall Thu, 10/14/2010 - 10:28
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angel-moon wrote:


Hello All,



I was wondering if someone could point me in  eright direction.  I have a 2811 router that I want to have you 2 different ISPs.  I would think the easiest way to go would be to have a primary ISP and a secondary one where the traffic flows through the Primary until it goes down then switches over to the secondary automatically and then back to the primary once it is back up.  Can anyone point me in the right direction?  FYI the router's outside interface, and both ISPs will be plugged into the same unmanaged 8 port switch unless it just can't be done line that.



Thanks in advance!


If you want one primary and the other secondary you can use IP SLA.  Note IP SLA configuration commands keep changing, this config example is for 12.4 -


ip sla 1

type echo protocol ipIcmpEcho x.x.x.x    <-- where x.x.x.x is the primary ISP's next-hop gateway from your router

frequency 10   <-- this means it checks every 10 seconds, feel free to change


ip sla monitor schedule 1 life forever start-time now


track 123 rtr 1  <--- the 1 in this line must match the ip sla number used


ip route 0.0.0.0 0.0.0.0 x.x.x.x  track 123  <--- where x.x.x.x is the same address used in the IP SLA config

ip route 0.0.0.0 0.0.0.0 y.y.y.y 254


how this works is that the primary default-route pointing to x.x.x.x is installed in the routing table. The other default-route is a floating static with an AD of 254 so it is not installed in the routing table. As long as the ping is successful it stays that way. If the ping fails then the primary route is removed and the floating static is then used. If the ping then starts to work again the floating static is removed and the primary default-route is reinstalled in the routing table.


Jon

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