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

[Mingui Zhang <[e-mail]>]

Suppose RG1=(PE1,PE2) using label space 1~5, RG2=(PE2, PE3) using label space 6~10. So PE2 is in 2 RGs.
But, PE1 can well use label space 6~10 for other RG, say RG3 and PE3 can use label space 1~5 for RG4. 

Thanks,
Mingui
>-----Original Message-----
>From: Jakob Heitz [mailto:[e-mail]]
>Sent: Friday, November 29, 2013 1:54 PM
>To: Mingui Zhang
>Cc: [e-mail]; [e-mail]
>Subject: Re: Why we consider the method of "label sharing for fast PE
>protection"
>
>I any PE is part of 2 RGs, then those RGs can not have overlapping label spaces.
>
>--
>Jakob Heitz.
>
>
>On Nov 28, 2013, at 6:16 PM, "Mingui Zhang" <[e-mail]>
>wrote:
>
>> 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