Robert Raszuk wrote:
To configure exit path selection such that you take optimal exit to
destination X vs destination Y you need mechanism to either
passively or actively measure it. The entire point I am trying to
make here is that sweet spot for such measurements is the edge of the
network and not on each host, VM, container etc ....
As I wrote:
Note that end to end multihoming works with the separation between
inter domain BGP and intra domain routing protocols, if BGP routers,
based on domain policy, assign external routes preference values
(metric) of intra domain routing protocols.
BGP routers are at the edge.
Of course even if I would carry selective destinations in IGP with
properly mapped metrics how would host learn about it when it has to
pick the src address from N available in end to end multi homing
principle ? Is the assumption again that hosts, VMs, LXCs
participate now in the IGP ?
I know poor source address selection is a flaw of current IP (both
v4 and v6).
And even if it would be a passive IGP listener how do you encode in
any IGP today which src address should be selected such that packets
wil not be dropped due to uRPF check by the upstream provider ?
For the solution, read the draft:
Any source address may be selected.
However, to enable source address filtering to discard packets with
source addresses not belonging to an ISP, it is useful to enable a
host, not some intelligent intermediate router, select a source
address compatible with an outgoing ISP. For that purpose, intra
domain routing protocols should maintain routing table entries with
not only preference values of an external routes, but also proper
prefixes to be selected for source addresses, if the entries are
chosen by a host.
Masataka Ohta
