Is it possible to see a Teredo address (from 2001::/32 block) in an IPv6 neighbor cache? For example, in the case of Junos, in the output of show ipv6 neighbors. As much as I tested, this is not possible because traffic leaving the Teredo client is already encapsulated in UDP/IPv4.

  • 2
    I don't think you will, as they aren't actually neighbors. Commented Oct 17, 2018 at 15:02
  • @MichaelHampton Do you mean that Teredo addresses are never configured on a physical interfaces and thus they are never a neighbor?
    – Martin
    Commented Oct 17, 2018 at 19:52
  • 4
    Teredo is a tunnel and has no neighbors. Neighbors are other IPv6 speaking devices on the same link. Teredo has none, as the link is virtual and no other devices are on it. Commented Oct 17, 2018 at 19:56
  • @MichaelHampton Yes, I think I understand this the same way. At least in Linux using Miredo Teredo client, the teredo interface(which is actually a tun interface) gets the IPv6 address from 2001::/32 block and traffic destined to IPv6 addresses leaving the Teredo host are encapsulated to UDP/IPv4. So indeed, the interface with Teredo IPv6 address has no neighbors. Also, as much as I understand the Teredo relay part, then they announce the 2001::/32 prefix, but do not have any interfaces with addresses from 2001::/32 address block, i.e there should be no neighbors from 2001::/32.
    – Martin
    Commented Oct 18, 2018 at 9:13
  • 1
    I think you should consider rewriting your comments to an answer, @MichaelHampton, so it can be accepted.
    – Teun Vink
    Commented Oct 19, 2018 at 12:24

2 Answers 2


You won't see Teredo addresses in the neighbor cache, because Teredo creates a virtual point to point link and therefore has no neighbors. A neighbor is another device (which, for this purpose, speaks IPv6) on the same Layer 2 link. But a Teredo connection has no such devices sharing its virtual link.

  • I wanted to make sure you saw this and this as they directly to relate to Server Fault. (By the way, I grew up in Austin, and my family still lives there. I was there on Thanksgiving, and I'm sure I will be back for Christmas, and maybe for my birthday that is four days later.)
    – Ron Maupin
    Commented Nov 25, 2018 at 2:24

If you are seeing teredo addresses in a neigbour cache then something is seriously misconfigured.

Teredo creates a virtual interface on the teredo client allowing it to communicate with other teredo clients and relays. This virtual interface is not an Ethernet-like interface, so it has no need for neighbour discovery.

Unlike with 6to4 teredo has no provision for running a network behind the teredo client. So teredo addresses should never be assigned to a real network segment and therefore should never appear in a neighbour cache.

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