Re: Best practice for redundancy when there're more than 2x ISP

Maybe... Grouping them by BGP community would do the trick when it comes to this failover scenario.

Too tired to think, need to look into it in the morning.

Regards,
Nish

are:you::ipv6:ready?

On 22 Sep 2010, at 21:50, Tech Guy <autechguy_at_gmail.com> wrote:

>> Hi GS,
>>
>> I have a very interesting real-life scenario, when I have to design redundancy for our network (ISP) that have upstream with 2 x ISP. It would also be an interesting scenario for CCIE candidates, as this one will make you think, not just about what option will work, but what will work best.
>>
>>
>> I would like to know your feedback. I have a design that works but I will tell you later, so that I will not distract a fresh discussion.
>>
>> Our design requirements are:
>>
>> - The back up link of an ISP should kick in (both for inbound and outbound) automatically when the its primary fails.
>> - In this case (primary of one ISP fails), we do not want all traffic goes via the remaining primary of other ISP.
>> - No traffic (inbound and outbound) should fall on the backup link when its primary (from the same ISP) is up.
>>
>>
>> To control the inbound traffic, we decide to use AS - prepend, and prefix length. I am more intrested in the controling of the outbound traffic.
>>
>> To control outbound traffic, I thought of MED as it is the most suitable for controling redundancy for routes from the same ISP. We can get ISP to send us MED, or we explicitly set MED inbound (this is not a really straight forward use of MED, but believe me, it works with one ISP). However, MED design does not work in case we receive routes from different ISPs.
>>
>>
>> Let's look at the below topology.
>>
>> /----------------- ISP1 (Primary) MED = 50
>> R1 ----------------- ISP2 (Primary) MED = 50
>> |
>> |
>> | iBGP
>> |
>> |
>> R2 ----------------- ISP1 (Backup) MED = 100
>> \----------------- ISP2 (Backup) MED = 100
>>
>>
>> The problem is that R1 only send R2 the best routes! E.g. from ISP1. If this best route has the same AS path lengh with the one from ISP2, then R2 will see the best coming from ISP2 because routes learnt from eBGP win over iBGP !!!
>>
>>
>> Other remaining options are:
>>
>> - Weight
>> - Local preference
>> - Origin
>> - AS prepend
>>
>> What is your recommended design option, and why?
>>
>>
>>
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Received on Thu Sep 23 2010 - 03:14:55 ART