Pekka,On 2 aug 2005, at 11.06, Pekka Nikander wrote:
1. Tunnelling over the very same protocol; e.g., IP-over-IP
I think there are operational reasons why might want to do this. Building an architecture based on this is probably flawed though.
2. Tunnelling a protocol over one at the same layer; e.g., IPv6 over IPv4
Here I disagree. This is not a problem of architecture but a clear example (subcase) of 1). This is not a flaw in the architecture.
3. Tunnelling a global lower-layer protocol over a higher layer protocol; e.g., IP over DNS, IP over UDP, or IP over HTTP
This is a flaw.
4. Tunnelling a local-scope lower-layer protocol over a global high layer protocol; e.g. Ethernet over IP
I agree that this probably is a flaw in the architecture but it is also currently used for cases where there is little or no choice. Implementing whole-sale DSL+PPPoE comes to mind (if I have misunderstood the use of tunneling here, please feel free to correct me).
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