On 12-okt-2005, at 15:29, marcelo bagnulo braun wrote:
right, but as was noted, a single bit is not enough for demux, so an
alternative context tag is needed.
No, I don't believe this is necessarily the case. I can imagine
different ways to accomplish this, but let me just describe the
simplest one.
Hosts A and B communicate. A has addresses A1 and A2. In the case of B
it's a bit more complex: B has ULID/locator addresses B1 and B2, but
these aren't valid locators for each other: B1 has the alternative
locator B1' and B2 has the alternative locator B2'.
The chosen ULIDs for a TCP session are A1-B1. However, at some point
B1 fails and the communication is rerouted to A2-B1'. The context has
tag X but therere is no shim header in the packets flowing from A to
B.
When B receives a packet, it can recognize that this is a shimmed
packet because the locator B1' is present. B then goes looking for a
context with ULID B1 on B's side and locator A2 at the remote side.
Since there is only one such context B finds the X context, rewrites
the addresses and the packet is handed over to TCP.
Now if an application tries to set up a session from A2 to B1, when A
tries to set up a new context Y B notices that this context and the
existing A1-B1 can't be disambiguated without a shim header so it
tells A to use the header for this context.
A2-B1' packets without a header are then still mapped to context X
while packets belonging to context Y are recognizable as such by their
context tag in the shim header.