High Available Data Centre Internet

[de1denta]

Hi,

We currently have a single data centre with 2 x 100Mbps internet links from a single ISP. The 2 links are routed and terminate on separate ISP switches/routers with a /30 IP address, the links terminate on 2 Cisco 3900 series routers in the DC. eBGP and iBGP has been configured to provide high availability. We are currently using a private BGP ASN from the ISP and /24 subnet which is routed to the primary 3900 router and to the backup 3900 router in the event of a primary router failure.

We are looking to add a second data centre for DR and we need the /24 to failover over to the DR data centre in the event that the primary DC fails. The second DC will only have a single 100Mbps internet connection as resiliency in DR is not required. I understand how eBGP/iBGP willl be setup and configured for both sites but I would like to know the pros/cons and peoples experiences of using a single ISP to provide internet connectivity for both Data Centres? I understand that I will need a public ASN if I use separate ISPs.

Is using a single ISP for all 3 internet connections acceptable? The circuits will be connected to resilient parts of the ISPs network.

If we decide to use a second ISP, would it be recommend to use ISP1 for the Primary and DR data centre primary links and ISP2 for the Primary data centre backup link?

Any help and your suggestions/experiences will be appreciated.

Thanks

[Edison Ortiz]

Ideally, you want different ISPs for each link. An ISP backbone failure will affect your entire operation and you will have no redundancy.

As for your second questions, many customers advertise their subnet without any BGP manipulation.

For customers on ISP A, they will primarily use your ISP A link.

For customers on ISP B, they will primarily use your ISP B link

For other customers, they will use the shortest AS_PATH length.

With this approach, you are fully utilizing both links which you are  paying for and avoids 'those disaster recovery testing windows' to test  backup links.

The question is, are you getting full internet routes? I assume not, with your 3900s.. This can create some designs concerns on egress traffic.

Regards,

Edison

[de1denta]

Hi Edison,

Thanks for the reply.

So in this scenario you would suggest using a seperate ISP for the 3 internet connections? ISP1 and ISP2 for the primary data centre routers and ISP3 for the DR data centre router?

Would there be any issues using 2 ISPs?

Example, ISP1 provides internet for the primary data centre router 1 and DR data centre router 1 and ISP2 provides internet for the primary data centre router 2?

Thanks for your assistance.

[Edison Ortiz · Accepted solution]

No issues using 2 ISPs. This design guidance is implemented on most /if not all/ of the medium to large corporations..