Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
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entries will age out fairly quickly but by that time all DVR hosts in the DVR domain will have an updated
host IP route for the VM.
Figure 72 DVR with VM Migration Across DVR domains
In the case of a VM migration across DVR domains, the mechanism is much the same. Again, the
GARP/RARP will be received by all DVR nodes, across both DVR domains. The DVR leaf, which used to be
the owner of the host route in the source DVR domain, will withdraw its host route while the DVR leaf,
which becomes the new owner of the host route in the target DVR domain, will signal the host route within
the target DVR domain only. All DVR leaf nodes across both DVR domains will have installed short-lived
ARP entries for the host in the process. Except that now, once these short-lived ARP entries are aged out,
knowledge of the VM host will disappear in the source DVR domain and subsequently any traffic destined
to that host from this DVR domain will have to follow the default routes toward the DVR controllers. The
result is a robust and efficient host-based routing architecture that is able to follow and keep track of all
data center host IPs.
Eliminating North-South Tromboning
North-south traffic tromboning is a phenomenon that can occur in the presence of geo-redundant data
centers where server subnets span both data centers and thus both data centers are advertising the
corresponding IP subnet of that server segment into the wider campus/branch network. The routers
operating in the wider campus/branch network typically have to make a routing decision based on the IP
subnet alone and will typically always choose the path to the nearest data center, which is not necessarily
the shortest path to the server host/VM that is mobile and could be located in either data center.
Depending on the network design, this can result in sub-optimal traffic forwarding and a higher latency
inflicted on the applications running from the data center.
Extreme Networks DVR architecture offers the capability of minimizing these traffic tromboning effects by
allowing the network administrator to identify those critical data center host IPs that act as termination
points for all client-server interactions for a given business application and then allowing those selected
host routes to be taken into consideration by campus/branch routers in order to always ensure the shortest
path to reach those data center resources.
Tip
Note that in modern data centers, not all host IPs communicate north-south with users. A
majority of those hosts are either backend databases or batteries of servers operating
behind load balancers that are used exclusively for east-west communication within the