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Beginner

OTV runs over IP, UDP or TCP

Hi All,

Just wondering what does OTV run on? Directly over IP, of UDP or TCP. When I did google search, I see that OTV uses TCP/UDP ports 8472. But the OTV documents say it only adds 42 byte overhead. With 42 bytes, I could not account for TCP or UDP headers in the encapsulation.

Has anyone have full capture of OTV encapsulated packet in Wireshark or something. I wanted to know how OTV is transported over IP network.

Thanks,

Mohan M

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Beginner

 Hi,

I assume its IP.

Note

The routing protocol used to implement the OTV control plane is IS-IS. It was selected because it is a standard-based protocol, originally designed with the capability of carrying MAC address information in the TLV. In the rest of this document, the control plane protocol will be generically called "OTV protocol".

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Hi Mohammed,

Thanks for the reply. I have already seen that picture. I need to know if OTV directly over IP, then what is the protocol number (like 1 for ICMP, 6 for TCP, 17 for UDP and so on). Or if it runs over TCP or UDP? I need to know how L2 packets are encapsulated in the Data Plane of OTV.

Thanks again for taking time to answer my question. Much appreciated.

Regards,

Mohan

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Beginner

It's actually Ethernet over MPLS over GRE.  Here is a screenshot of a wireshark capture of the OTV packet in transit:

The total overhead is 42, like you said.  This consists of:

  • New Outer Ethernet Header – 14 bytes
  • New Outer IPv4 header – 20 bytes
  • New GRE Header – 4 bytes
  • New MPLS Header – 4 bytes

In this particular wireshark capture the OTV edge routers are addresses 150.1.78.7 and 150.1.38.3, which can be seen in the outer IP header.  The traffic that is tunneled is between end hosts 172.16.0.2 and 172.16.0.3.  Specifically this packet is a 64 byte ping between the two of them.

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Cisco Employee

As mentioned above OTV packets are GRE packets. If you need more details I have written a very basic blog related to how we can do packet capture of OTV packets on our routers, which in turn helps us understand how an OTV packet looks like. http://stayinginit.blogspot.in/2013/12/embedded-packet-capture-for-otv.html

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