RE: Why we consider the method of "label sharing for fast PE protection"

[Mingui Zhang <[e-mail]>]

Hi Bruno, 

So you suppose the label used in an RG cannot be used again out of the RG. That is not correct.
Please find my comments inline [Mingui].

<snip>
>[Bruno2] Let's assume:
>- 5 PE in the group, hence sharing the same range of labels (e.g., 1~1100).
>- 5 VPNs in connect to this group of PE, 2 of which being dual-homed (VPN1 &
>VPN2).
>
>With label sharing:
>Label:1	2	3	4	5
>
>PE1	VPN1	x	x	x	x
>PE2	VPN1	VPN2	x	x	x
>PE3	x	VPN2	x	x	x
>PE4	x	x	VPN3	x	x
>PE5	x	x	x	VPN4	VPN5
>
>All labels marked as "x" are burned/lost because of the label sharing.

[Mingui] Not true. Where we got this constraint? For an explicitly example, PE4 can well use label 1,2,4,5. 

[Mingui] I anticipate you assume PE1~PE5 are forming an RG, so that once a label is used it is used across the RG. I need to point out that the unit of "RG" is independent of PEs. It depends on the VPN connections. I saw Zhou Peng has already given examples on this point. 

<snip>

>[Bruno2] not always. There is public/ietf example for this:
>draft-l3vpn-legacy-rtc-00

[Mingui] It's designed to be incrementally deployable in the network. The trick is confined in the RG. Other P and PE routers are unaware of the change.

[Mingui] I guess you may change to imagine the scenario that operator need a legacy PE and a label sharing PE form an RG. Let's consider the analogy that the operator interconnects two switches using LAG while one of them does not support LAG at all. :) 

[Mingui] Thanks for continuing the discussion. I think the discussion about label ranges reservation in another thread is related to our discussion. To my understanding, the conclusion is that it's not OK to require a label block to be supported across multiple PEs. A possible escape is to resort to a higher-layer authorized entity out of the RG to assign the label.

Thanks,
Mingui