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BGP peering with ISP

Hello Guys

 

I have a scenario where I would like to have your insights.

 

1. Client having Main site and DR site connected to same ISP with public IP line.

2. The client has acquired a public IP block (/24) and would like to use same on both main and DR sites.

 

Would this be possible through BGP? How can we advertise the same IP block on 2 sites?

 

The sites need to be in an active-active scenario.

 

Thanks

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VIP Expert

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

Will both the main and DR site be able to reach the public hosts independent of the ISP connection?

If yes, yes both sites can advertize the same public address block.

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Yes ISP does not advertise a block lesser that /24.

Could you please clarify "able to reach public hosts independent of ISP connection"?

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you can advertise the same public subnets /24 on both sites main and DR if you would like to have redundancy.

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It s only in a DR scenario that the link will be used. We are not really looking at redundancy here.

But my question is if we can really advertise the same block to the same ISP on different sites.

 

If yes, could anyone please elaborate... 

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Dear Ramdeo Baba,

Theoretically u can do it...however in real world it will cause asymmetric routing.You can try this in GNS3

So as suggested by  ttemirgaliyev split the block in /25

Regards.

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Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages whatsoever (including, without limitation, damages for loss of use, data or profit) arising out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

If you're going to advertize the same address block, from two different BGP peers, whether to the same ISP or different ISPs, the expectation is, you can get to or from that address block along either path.  I.e. you need an "internal" path between your two BGP peers.  Otherwise, the "critical" BGP path fails, you continue to advertize an address block that's unreachable.

There's no need to split your block unless you were trying to manually load balance using your two paths.

As another poster noted, you might have asymmetrical routing (depending on path costing), but from a pure L3 perspective it doesn't matter.  It can, though, matter to stateful devices like firewalls.  The latter might be addressed by firewalls at both sites sharing state information.

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Frequent Contributor

your client also need AS to advertise IP block (/24) from one place.

 

probably your client can split IP block (/24) for 2 IP blocks (/25) but providers do not accept networks less than /24