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BGP load balancing

Do tier 1 ISPs block </19 and higer prefixs? in that case.

lets say that i am using bgp to connect to ISP A and ISPB. which are connected to tier 1 ISP which is blocking </19 prefixes.

so when i advertise my /24 using bgp for load balancing through ISPA. ISPA only advertises the agregate to Tier 1 ISP and Tier 1 block /24 from ISPA and ISPB. right?

so if i loose the path from ISPA, i loose connection to the internet(inbound). as Tier 1 will not route the traffic through ISPB as it is blocking prefixes greater than /19.

The reason i ask is because if i go to Sprint ot UUnet BGP page , it says that they reserve the right to aggregate routes.

Any information would be appreciated.

1 REPLY
Purple

Re: BGP load balancing

Hi Parwal,

Is your IP block provider-independent address space from one of the internet addressing registries ? If that is the case, most providers will not filter out your /24. A large proportion of the Internet routing table is made up of /24s.

As for that note from the Sprint/UUNet page, note that they are talking about "aggregating" routes, not filtering them. Therefore, if your address space is obtained from either of these providers, they can aggregate it into their larger block before announcing to other providers. That does not mean they will necessarily filter it.

Hope that helps - pls rate the post if it does.

Paresh

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