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configuring Redundancy with Two lease lines

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Oct 25th, 2010
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Hi all,

Having some problems in configuring redundancy using two lease line between two cisco 1841V routers.

One router is at site A and another is in Site B.

Both are /30 point to point links where one is ethernet and another is serial.

Any heads up on how i should start with this

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Mahesh Gohil Mon, 10/25/2010 - 20:40
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Hi ali,

Redundancy between ethernet and serial is little challenging with static router..

Can you confirm which dynamic routing protocol you are running between

both the sites.

If you are running static then redundancy is not possible ...i request you to run some dynamic protocol..

please confirm


rtjensen4 Tue, 10/26/2010 - 05:05
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If you want simple redundancy without load-sharing, you can use a floating static route.

ip route

ip route 250

If the primary connection goes down (interface goes down/down), the first static route will disappear and the static route with AD of 250 will become the route that's used.

If you want any load-sharing / load balancing, you'll likely need a dynamic protocol.

Mahesh Gohil Tue, 10/26/2010 - 06:55
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Hi rtjensen4 ,

Your solution is ok with Serial interface/ or ethernet interface when router notice line protocol down but for ethernet

interface router will not notice this as down when far end goes down (if two routers are connected via. telco or some via some other device)

and static routes will not clear from routing table which leads to black-holing

Ali need to use some routing protocol or something like IP SLA.

If he is using static routing , need to change to some dynamic protocol. (I would suggest to go with BGP...b'se i love bgp...he he he)



rtjensen4 Tue, 10/26/2010 - 07:03
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I agree, the router has to notice that the Line protocol goes down. I'd probably use EIGRP or OSPF instead of BGP, EIGRP is easier to configure and quicker to converge. If for some reason a dynamic routing protocol isn't an option, you could use an IPSLA and tie the static route to it.

The IP SLA would ping the other side of the primary link, if it doesn't respond, remove the static route and put the other in place.

Not saying one idea is better than the other, just trying to throw out whatever ideas I cna think of.

rogue7860 Tue, 10/26/2010 - 12:51
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unfortunately it is using  static routes and it is connected via telco. As due to some network management issues dynamic routing is not an option.

so the only the option is IPSLA??

rtjensen4 Tue, 10/26/2010 - 13:43
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You can use the simple floating static, but that will only "Trigger" if the router sees the line protocol go down. The IP SLA tied to a static route will be a bit more accurate than just the floating static alone.

rogue7860 Tue, 10/26/2010 - 16:36
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Thanks rtjensen4 for all your help,

Floating routes look simple enough to configure, lets say i have these routes on my router

link 1 ip route
link 2 ip route 180

where a metric has been set to the second link as that was is least desirable(since this will be purely used for redundancy not load sharing).

but i also want to place a time delay as if link 2(link 1 is down) does go active it stays there for 3 minutes and then the router checks if link 1 is up or not.

Could i use the IP SLA here??


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