Network Virtualization using Extreme Fabric Connect

Network Virtualization Using Extreme Fabric Connect
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DVR Host Tracking and Traffic Forwarding
It is worth looking at how DVR learns and tracks data center hosts as well as how it handles traffic
forwarding for L3 flows within the data center from which it will become apparent how powerful DVR is
compared to competing data center architectures.
Pretty much every operating system, once configured with a Default Gateway IP, will proceed out of its
own initiative to perform ARP resolution for that gateway IP in order to obtain the gateway’s MAC address
which can then be used to transmit any traffic destined outside of the host’s own IP subnet.
If the DVR leaf has an active DVR interface for the server segment on which the ARP request is received, it
is the DVR leaf which will handle the ARP exchange directly, for the DVR Gateway IP, by providing the host
with the DVR Gateway MAC in use on the segment.
Tip
In the DVR implementation, the DVR Gateway MAC is always the same across all DVR
segments: 00:00:5e:00:01:25 for IPv4 (will be 00:00:5e:00:02:25 for IPv6). This allows a
better use of silicon hardware resources on the DVR leaf nodes to scale to many more
routed MACs than would be otherwise possible.
Responding to host ARP requests for the DVR Gateway IP, allows the immediately attached DVR leaf node
to discover the existence of the host. The very same DVR domain I-SID which was used by the DVR
controllers to provision the DVR interface on the DVR leaf nodes is used by the DVR leaf nodes to advertise
the existence of the server/VM host IP, in one efficient single update to all other DVR leaf nodes and DVR
controllers. This allows all nodes within the DVR domain to build and maintain IP host tables covering every
host within that domain. The DVR controllers will in their turn use the DVR Backbone I-SID to advertise the
existence of host IPs across other DVR domains. The result is that a DVR leaf will be aware of all host IPs
within its own DVR domain, while the DVR controllers will be aware of all host IPs across all DVR domains.
Figure 68 DVR’s Distributed Anycast Gateway in Action
This raises an important point around the maximum host scaling of DVR. A DVR leaf will only need to
program host IP routes for IP hosts located within the DVR domain. Whereas a DVR Controller will not only
program host IP routes for IP hosts located within the DVR domain but also every host which is seen in
other DVR domains if these hosts are located on L2 VSN segments for which the DVR Controller has a local
DVR gateway IP interface. Hence for DVR domains which share the same DVR enabled L2 VSNs the
maximum DVR host scaling will be network wide. Whereas if DVR enabled L2 VSNs are not extended
across DVR doamins then the maximum DVR host scaling limit will apply to the DVR domain only.