nx.os.and.cisco.nexus.switching.2nd.edition.1587143046

6. The hellos are passed to the control protocol process.
Note
The control-plane routing protocol used to implement the OTV is IS-IS, which has
TLV support to carry MAC address information and is a standard-based protocol.
The customer or end user does not need to configure any IS-IS information to get OTV
to work.
The use of the ASM group to transport the Hello messages enables the Edge Devices to
discover each other as if they were deployed on a shared LAN segment.
Although data centers offer forms of physical security access controls and are controlled
environments, you can leverage the IS-IS HMAC-MD5 authentication feature to add an
HMAC-MD5 digest to each OTV control protocol message. The digest enables
authentication at the IS-IS protocol level, which prevents the unauthorized routing message
from being injected into the network routing domain. As a result, only authenticated devices
will be allowed to successfully exchange OTV control protocol messages between them and
become part of the same overlay network. Because the OTV Edge Devices have a full mesh
of adjacencies, here is how the MAC address advertisement happens from each OTV Edge
Device:
1. The OTV Edge Devices learn new MAC addresses on the internal interface; this is
traditional Layer2, switching data-plane learning.
2. An OTV Update message is created containing information for the MAC addresses
that were learned in the OTV internal interfaces. The MAC addresses are OTV
encapsulated and sent to the Layer 3 core. Again, the IP destination address of the
packet in the outer header is the multicast group configured under the OTV overlay
interface used for control protocol exchanges.
3. The OTV Update is optimally replicated in the transport and delivered to all remote
Edge Devices that decapsulate it and hand it to the OTV control process.
4. The MAC reachability information is populated in the MAC address hardware tables
of the OTV Edge Devices. The only difference is that a traditional MAC address is
associated with a physical interface; OTV-learned remote MAC addresses have MAC
address entries associated to the IP address of the join interface of the originating
Edge Device.
Because you advertise reachability of MAC addresses from the control-plane IS-IS
protocol, the same logic can be applied for MAC address withdraw and MAC address
movements from one data center to another.
Note
The Nexus 7000 has a default Layer 2 MAC address aging time of 1800 seconds (30
minutes) and a default ARP aging timer of 1500 seconds (25 minutes). By setting the
default ARP < CAM, timeout results in refreshing the CAM entry before it expires