lamav Sat, 03/21/2009 - 07:17
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Default static to one ISP and floating default static pointing to the backup ISP.

ip route

ip route 220

lamav Sat, 03/21/2009 - 08:17
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Unnecessarily complicated.

He doesnt want load sharing. He wants hot/standby ISP redundancy.

Statics are the way to go, papi.

Mohamed Sobair Sat, 03/21/2009 - 14:13
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Victor, Giu

I have different suggestion.

the static default routs are never removed from the routing table unless the "Arp-cache" timed out, and this takes very long period by default.

Conditional Advertisment is also not required in his case.

I would recommend "Reliable Static routing with Object tracking" as an option


Normal BGP.



lamav Sat, 03/21/2009 - 14:33
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I honestly would stay away from BGP because it doesnt buy you anything, just complicates the scenario.

The static route with object tracking sounds good, thinking off-the-cuff.


rpfinneran Sun, 03/22/2009 - 01:02
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You really should use BGP for this. It would be pretty simple, just setup eBGP with weight command to dictate preferred ISP. Also, ensure both ISP's advertise default route to you (make sure you filter so as to not make your AS a transient one). You will also need to be sure that neither ISP is originating your networks, you want that to happen on your network.

The issue with object tracking and static routes is that obviously if you are not advertising your internal networks to each ISP, then they must be originating them. So, if the primary link goes down, depending on physical media, it is possible that the primary ISP would continue to advertise your routes, creating a black hole scenario.

Here are the configs that I would suggest. Then just ask your ISP's to advertise the default route over these BGP connections...

conf t

ip prefix-list defaultnet seq 5 permit


ip prefix-list deny_default seq 5 deny

ip prefix-list deny_default seq 10 permit le 32


route-map Prepend deny 5

match ip prefix-list defaultnet

route-map Prepend permit 10

set as-path prepend xxxx xxxx xxxx xxxx xxxx xxxx xxxx


router bgp xxxx

network blah mask blah

network blah mask blah


neighbor remote-as yyyy

neighbor weight 200

neighbor description *** ISP 1 | Primary ***

neighbor prefix-list defaultnet in

neighbor prefix-list deny_default out


neighbor remote-as zzzz

neighbor weight 100

neighbor description *** ISP 2 | Backup ***

neighbor prefix-list defaultnet in

neighbor route-map Prepend out



Mohamad Qayoom Sun, 03/22/2009 - 20:20
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What would you guys recommend if load sharing is needed in this situation?

rpfinneran Mon, 03/23/2009 - 03:56
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If load sharing is preferred, just check this forum, there are a bunch solutions here for that scenario.


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