Iljitsch van Beijnum wrote:
There are two problems with allowing routers to rewrite source addresses:1. The routers must know which packets are "legacy" and can't have their source address changed vs which packets are controlled by shim6 or another mechanism that can handle rewritten source addresses.2. In current shim6, only previously negotiated source addresses may be used, which means the shim6-enabled hosts in a site and the rewriting routers must coordinate their efforts so correspondent hosts don't see unexpected source addresses.
FWIW draft-nordmark-shim6-esd-00.txt is on the way to the I-D directory, and it has some ideas for how to address this.
The first issue is readily solvable by simply having shim6 hosts put a magic value in the upper 64 bits of the source address that indicates "rewriting permitted".
Or next hdr = IPPROTO_SHIM6.
The second issue is a bit more complex but not fatally so, IMO. So if we want to, we can explore source address rewriting.The reason we haven't done so (or, at least, the reason I haven't pushed this) is that it doesn't solve anything in the short term because we can't depend on this capability in the forseeable future, so shim6 must also work without the rewriting capability present.
Agreed. Getting a basic locator agility mechanism which works without assuming router rewriting has been the most important thing so far.
Erik