Stephane -
> -----Original Message-----
> From: spring [mailto:[email protected]] On Behalf Of
> [email protected]
> Sent: Tuesday, August 25, 2015 4:28 PM
> To: Peter Psenak (ppsenak); Eric C Rosen; Pushpasis Sarkar; SPRING WG
> Subject: Re: [spring] SRGBs, indexes, and topologies within a domain
>
> Hi Peter,
>
> As I already pointed to Les, using an offset creates some holes in index space
> that we need to manage when extending a block.
>
> Let's say that we have SRGB [100-199] (to simplify) and you divide your block
> in two so you will have topology #1 using [100-149] and topology #2 using
> [150-199] using an offset of 50.
> Now I need to add a 51th node in my network, I cannot use index 51 because
> it will overlap with topology#2 :(, so I will need to skip indexes from 51 to
> 100,
> and restarts my numbering with index 101. This management of holes is not
> automated.
[Les:] The same issue arises w topology specific SRGBs. Let's take an example.
I am setting up my network for SR. I anticipate that I will need 500 labels per
topology and I anticipate a maximum of 5 topologies. In order to be prepared
for the "worst case" I decide to allocate enough for 1000 labels/topology and
10 topologies and I reserve it all up front because - as you have documented in
an earlier post - assuming I can allocate additional SRGB space when I need it
without either rebooting the node or shutting down some applications I am using
is not safe.
Using the offset approach:
srgb 16000-25999
srgb offset topology 1 1000 !Please don't quibble about syntax :-)
srgb offset topology 2 2000
I only configure offsets for the topologies that are currently active. Since I
have reserved the label space in a topology independent way I am free to
allocate space for each topology only when they are needed - and if I find that
I am using far less than 1000 labels when the next topology is enabled I could
choose to do:
srgb offset topology 3 2500
And now I can support more topologies than originally planned for if necessary.
Now let's look at a per topology approach. You could allocate topology specific
SRGBs only when you need them, but this leaves you open to cases where the
desired label space is in use - so again you decide to allocate all of the
label space up front. But now you have to decide how many SRGBs to allocate.
So you do:
srgb 16000 16999 topology 0
srgb 17000 17999 topology 1
...
srgb 25000 25999 topology 9
You can support 10 topologies - but if you find that 1000 labels/topology is
far more than you need but 10 topologies is fewer than you need you can't
easily accommodate the additional topologies without reconfiguring the srgb's.
The key points here are:
o Allocating all the labels you will ever need up front is the safest method
o Allocating a single SRGB and partitioning it as you need it provides a bit
more flexibility
o In either approach you likely have unused label space ("holes").
Clearly either method will work .
But the main point is that the single SRGB is not more problematic than per
topology SRGB (as your reply suggests) - if anything it is more flexible.
Les
>
> Best Regards,
>
> Stephane
>
> -----Original Message-----
> From: Peter Psenak [mailto:[email protected]]
> Sent: Tuesday, August 25, 2015 13:18
> To: LITKOWSKI Stephane SCE/IBNF; Eric C Rosen; Pushpasis Sarkar; SPRING
> WG
> Subject: Re: [spring] SRGBs, indexes, and topologies within a domain
>
> Hi Stephane,
>
> On 8/25/15 12:58 , [email protected] wrote:
> > Hi Peter,
> >
> >>> 1. If a new topology is added by use of the MT features of an IGP,
> >>> then a new set of prefix-SIDs must be provisioned. This seems like
> >>> a major provisioning task. The alternative would be to have an SRGB
> >>> per topology; then when you add a new topology, you only have one
> >>> quantity to provision (or one per platform perhaps). I hear some
> >>> hand-waving about how easy it is to provision new prefix-SIDs for
> >>> every new topology, but ...
> >
> >> I will keep repeating myself that such provisioning can be made
> automatic, so the above point is not really convincing to me.
> >
> > Could you explain how ? Based on past discussions, it does not seem to be
> so easy.
>
> simply by associating an offset and size from SRGP on a per topology basis.
>
> Example:
>
> SRGB 1600-24000
>
> I would assume that when you start to assign your SIDs for the default
> topology, you would not pick random values, but start from the beginning. So
> let' assume you are using 16001 to 16500 for nodes in default topology.
>
> Now you need to add a new topology. You configure and offset of 2k for it,
> so the advertised SIDs for the new topology would start from 18001.
> If we assume that the 2k would be a reasonable size for each topology you
> can have 4 topologies with 2k SIDs per topology.
>
> If for whatever reason you run out of the SID space in any topology, you can
> configure another offset for those SIDs which do not fit into the existing
> range for such topology.
>
> All of the above is internal to the node and no per topology SRGB
> advertisement is required. You advertise unique SID on a per prefix and per
> topology basis, but you do not need to configure each SID manually.
> Al you need to configure is the single prefix SID and per topology
> offset/size.
> It gives you the same simplicity for configuration as per topology SRGB, but
> without the need to advertise SRGB per topology.
>
> thanks,
> Peter
> >
> >
> > Best Regards,
> >
> > Stephane
> >
> >
> >
> >
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