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Webcast-Catalyst9k
New Member

multihomed

guys if we have two isp on one router.......so what is the way to send all routes to one isp and if it fails it shd go to other isp????

8 REPLIES
Blue

Re: multihomed

Default static to one ISP and floating default static pointing to the backup ISP.

ip route 0.0.0.0 0.0.0.0

ip route 0.0.0.0 0.0.0.0 220

Hall of Fame Super Silver

Re: multihomed

Hello Khan,

if using BGP the right tool is

BGP conditional advertisement

see

http://www.cisco.com/en/US/docs/ios/12_2t/12_2t4/feature/guide/ftbgpri.html#wp1023979

this way you can start to advertise to ISP2 only when first session fails

Hope to help

Giuseppe

Blue

Re: multihomed

Giuseppe:

Unnecessarily complicated.

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

Statics are the way to go, papi.

Re: multihomed

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

OR

Normal BGP.

HTH

Mohamed

Blue

Re: multihomed

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.

Victor

New Member

Re: multihomed

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 0.0.0.0/0

!

ip prefix-list deny_default seq 5 deny 0.0.0.0/0

ip prefix-list deny_default seq 10 permit 0.0.0.0/0 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 1.1.1.1 remote-as yyyy

neighbor 1.1.1.1 weight 200

neighbor 1.1.1.1 description *** ISP 1 | Primary ***

neighbor 1.1.1.1 prefix-list defaultnet in

neighbor 1.1.1.1 prefix-list deny_default out

!

neighbor 2.2.2.2 remote-as zzzz

neighbor 2.2.2.2 weight 100

neighbor 2.2.2.2 description *** ISP 2 | Backup ***

neighbor 2.2.2.2 prefix-list defaultnet in

neighbor 2.2.2.2 route-map Prepend out

end

wr

Re: multihomed

What would you guys recommend if load sharing is needed in this situation?

New Member

Re: multihomed

If load sharing is preferred, just check this forum, there are a bunch solutions here for that scenario.

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