Cisco Overlay Transport Virtualization (OTV)

Peter Welcher
Architect, Operations Technical Advisor

This blog provides a link to the CMUG presentation on Cisco Overlay Transport Virtualization (OTV) I gave in Columbia, MD on 1/19/11. I have also added some supplementary info you may find useful below.

The OTV CMUG presentation can be found (in PDF form) here. It consists of numerous slides of useful information I assembled that supplement concepts and graphics based on the Cisco Networkers BRKDCT-2049 presentation.

The first version of OTV requires manual filtering of FHRP (First Hop Routing Protocol: HSRP / VRRP / GLBP) and ARP information for FHRP gateways between the data centers interconnected by OTV.

I have adopted and annotated the HSRP-filtering sample configuration from the BRKDCT-3060 below, in the hopes it will be useful to you. This supplements the FHRP (First Hop Routing Protocol) blog I previously wrote.

The following example assumes you’re doing OTV in a dedicated VDC “on two sticks”, i.e. with one “inside” interface and one “outside” or WAN-facing interface. It should be easy to adopt it to other OTV designs, but the two stick model is the easiest / most obvious way to explain the configuration sample below.

Configuring Manual HSRP and HSRP Gateway VMAC ARP Filtering

!!! Create and apply the policies to filter out HSRPv1 messages !!! between the two datacenters.
ip access-list ALL_IPs
10 permit ip any any
mac access-list ALL_MACs
10 permit any any
ip access-list HSRPv1_IP
10 permit udp any eq 1985
mac access-list HSRPv1_VMAC
10 permit 0000.0c07.ac00 0000.0000.00ff any
vlan access-map HSRPv1_Localization 10
match mac address HSRPv1_VMAC
match ip address HSRPv1_IP
action drop
vlan access-map HSRPv1_Localization 20
match mac address ALL_MACs
match ip address ALL_IPs
action forward
vlan filter HSRPv1_Localization vlan-list 600-1000
!!! Enable VACL processing on IP packets on OTV VDC internal
!!! interface.
!!! This blocks any traffic to the all-routers IP on UDP port !!! 1985, also traffic from an HSRP MAC address. This keeps one !!! side of the OTV from responding to an ARP for the default !!! gateway IP from the
!!! datacenter at the other side. (Configure it on both ends.)
interface Ethernet1/2
mac packet-classify
!!! Apply a route-map on the OTV control plane to avoid
!!! communicating vMAC info to remote OTV edge devices
mac-list HSRPv1-vmac-deny seq 5 deny 0000.0c07.ac00 ffff.ffff.ff00 ANY
mac-list HSRPv1-vmac-deny seq 10 permit 0000.0000.0000 0000.0000.0000 ANY
route-map stop-HSRPv1 permit 10
match mac-list HSRPv1-vmac-deny
otv-isis default
vpn Overlay101
redistribute filter route-map stop-HSRPv1

Exercise for the Reader

Produce versions of this for VRRP or GLBP based on the info in the blog article above, and post as a comment to this article.

One response to “Cisco Overlay Transport Virtualization (OTV)

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Nick Kelly

Cybersecurity Engineer, Cisco

Nick has over 20 years of experience in Security Operations and Security Sales. He is an avid student of cybersecurity and regularly engages with the Infosec community at events like BSides, RVASec, Derbycon and more. The son of an FBI forensics director, Nick holds a B.S. in Criminal Justice and is one of Cisco’s Fire Jumper Elite members. When he’s not working, he writes cyberpunk and punches aliens on his Playstation.


Virgilio “BONG” dela Cruz Jr.

CCDP, CCNA V, CCNP, Cisco IPS Express Security for AM/EE
Field Solutions Architect, Tech Data

Virgilio “Bong” has sixteen years of professional experience in IT industry from academe, technical and customer support, pre-sales, post sales, project management, training and enablement. He has worked in Cisco Technical Assistance Center (TAC) as a member of the WAN and LAN Switching team. Bong now works for Tech Data as the Field Solutions Architect with a focus on Cisco Security and holds a few Cisco certifications including Fire Jumper Elite.


John Cavanaugh

CCIE #1066, CCDE #20070002, CCAr
Chief Technology Officer, Practice Lead Security Services, NetCraftsmen

John is our CTO and the practice lead for a talented team of consultants focused on designing and delivering scalable and secure infrastructure solutions to customers across multiple industry verticals and technologies. Previously he has held several positions including Executive Director/Chief Architect for Global Network Services at JPMorgan Chase. In that capacity, he led a team managing network architecture and services.  Prior to his role at JPMorgan Chase, John was a Distinguished Engineer at Cisco working across a number of verticals including Higher Education, Finance, Retail, Government, and Health Care.

He is an expert in working with groups to identify business needs, and align technology strategies to enable business strategies, building in agility and scalability to allow for future changes. John is experienced in the architecture and design of highly available, secure, network infrastructure and data centers, and has worked on projects worldwide. He has worked in both the business and regulatory environments for the design and deployment of complex IT infrastructures.