ZNDP 034 – Data Center Interconnect Design Use Case with BGP With Tim McConnaughy

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Data Center Interconnect

We are joined today with my good friend Tim McConnaughy and he brings us our design case study for today’s show! This show is all about Data Center Interconnect Design, its a design use case with BGP.  There is BGP, eBGP, and iBGP. This is a real customer solution deployed today in the wild so lets get into it!!

Guest Expert: Tim McConnaughy

Today’s expert is Tim McConnaughy.  Tim holds a CCIE in Routing and Switching, has 8 years of experience in network operations, design and architecture. Tim has travelled the world doing data center colocation builds/refreshes/migrations, remote office network redesigns/implementations, and as a Cisco Advanced Services NCE has worked with very large enterprise customers to deliver network designs to solve business needs.

1. High level summary of Data Center Interconnect solution

From a technology solution perspective, we deal mainly with eBGP and iBGP to facilitate the Data Center Interconnect from both the Service Provider side and our own.

Business Drivers, Requirements, & Constraints for Data Center Interconnect

    • Network in transition. The main campus was closing and the Data Center assets were needing to be moved to a new colocation. The staff was relocating to other various campuses.
  2.  
    • The customer already had one data center which was connected to a MAN on which the old campus and some other old sites were connected. There were new fiber purchased to connect the old and new data centers as well as to allow those remote sites on the MAN to migrate. The plan was to decommission the old campus, data center and MAN and stand up the new data center with new connectivity in phases.
  3.  
    • The major constraints were that the old Campus/Data Center/MAN had to keep operational while the new data center and new fiber runs were completed or purchased. A transition network was also set up to move the old data center data to the new data center servers

2. Full list of technical solutions that were compared.

    • Customer came with a preliminary design which included eBGP between the 2 Data Centers and EIGRP as well as a full redistribution between the two planned for every hop-on / hop-off point.
  2.  
    • In working with the customer we defined some areas of improvement, such as opportunities to keep the BGP path attributes intact for better path selection and limit points of redistribution.
  3.  
    • After further exploration including an all-day whiteboard session, we identified that the proposed topology closely mimicked a CLOS spine/leaf topology which lent itself well to a full eBGP design.
  4.  
    • This actually greatly simplified bringing in the MPLS L3 VPN provider into the WAN and setting up path preference and path redundancy between the two data centers.

 3. Discuss the technical solution chosen and why

The more we investigated good redistribution points and how it impacted traffic flow and complexity of path preference, the more we kept landing on BGP. There were a few prior constraints, for example, the firewalls use OSPF in the services towers, and the campus/local data center runs EIGRP and need to communicate directly, so there is some redistribution, but for the most part the vision of a CLOS topology was realized.

4. What other technical solutions were there beside the Data Center Interconnect solution?

If the services towers were designed differently and had not been self-contained islands we would likely not have ended up with the same topology, because eBGP is not as good at convergence as a traditional IGP, and if the lines were much less sharp between services, there would not have been as much of a drive to segment them from a traffic flow perspective. This would have clearly indicated a simple approach with a single IGP domain. 

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