On 18/04/2009, at 12:08 PM, Paul Vixie wrote:
i should answer something said earlier: yes there's only 14 bits of tag and yes 2**14 is 4096. in the sparsest and most wasteful allocation scheme, tags would be assigned 7:7 so there'd be a max of 64 peers. it's more likely that tags would be assigned by increment, but it's still nowhere near enough for 300+ peers. however, well before 300 peers, there'd be enough staff and enough money to use something other than a switch in the middle, so that the "tagspace" would be per-port rather than global to the IXP. Q in Q is not how i'd build this... cisco and juniper both have hardware tunnelling capabilities that support this stuff... it just means as the IXP fabric grows it has to become router-based.
On Alcatel-Lucent 7x50 gear, VLAN IDs are only relevant to that local port. If you want to build a "VLAN" that operates like it does on a Cisco switch or something, you set up a tag on each port, and join the tags together with a L2 switching service. The tag IDs can be different on each port, or the same... it has no impact. -- Nathan Ward