Re: [Bier] Questions on draft-eckert-bier-te-arch-01
Toerless Eckert <eckert@cisco.com> Sat, 17 October 2015 00:46 UTC
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Date: Fri, 16 Oct 2015 17:46:36 -0700
From: Toerless Eckert <eckert@cisco.com>
To: Caitlin Bestler <caitlin.bestler@nexenta.com>
Message-ID: <20151017004636.GA9888@cisco.com>
References: <55DF5BAD.9060003@juniper.net> <20151007221035.GA26709@cisco.com> <561BFD2C.8090708@juniper.net> <20151013000257.GA13911@cisco.com> <56214683.5090900@juniper.net> <20151016194126.GA21691@cisco.com> <56217075.5090402@nexenta.com>
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Subject: Re: [Bier] Questions on draft-eckert-bier-te-arch-01
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Inline. On Fri, Oct 16, 2015 at 02:47:33PM -0700, Caitlin Bestler wrote: > I think I'm understanding BIER-TE finally, but I have a few questions to > confirm my understanding. > > How does an application use this? > > In particular, how is this done so the overhead of determining the > end-to-end path is not > imposed on the host or BFIR on a per packet basis? I don't think we've done a lot of brainstorming how to do end-2-end BIER where the two ends are actual applications instead of transport services gateways, eg: BIER-PE or the like (encap/decap native IP multicast or MPLS multicast). Assuming we had end-to-end bier, for BIER proper you'd have a 1:1 mapping between receiver and a bit in the bitstring, and its a matter of the API we build whether or not we hide these bitstrings. In BIER-TE you'd have to have like in other TE solutions some upfront magic that determines the shape of the overall tree. Eg: PCE controller or so. This is not a BIER-TE problem, this is a TE problem. If you want to build something like Steiner trees than the overall tree would want to change when you add/delete a receiver. If thats the traffic optimization needed, then worst case the PCE controller would need to give you for each possible combination of receivers a different bitstring. Not really difficult, but potentially a bit of upfront calculation depending on how many receivers you have and how many subsets are of interest. Again, this alculation would need to be done however you'd want to do TE, BIER or whatever else. Just the output being a bitstring is BIER-TE specific. If the path towards each receiver should not change whether or not other receivers are included into the tree or not, then it gets easier: The PCE controller would give you for each candidate reciver a bitstring, and the actual bitstring you want to use in your BIER packet is just the OR of the bitstrings for each receiver. > What is the stability of these derived bits? Are we preventing > transitory renumbering of internal links somehow? Assignment of bit-indices to links or BFRs or the like is all just software in the BIER-TE controller software, For path selection it may consult some external generic PCE controller or perform those functions itself. You can reuse a particular bit-index as soon as that bit-index is not used for anything else in any running BIFT or BFIR adjacency. This is really only a problem when the network growths. When you have link-failure, you do not reassign bits, you just need to update the bitstrings on the BFIR for packets to take alternative paths. > How often does the mapping of a destination IP > address to intermediate paths to be followed hold? IN BIER-TE you don't see the path in the bitstring, and it changes automatically because of routing. In BIER-TE its fully or partially visible. Its really just a matter of your policy when/how you want to change it. Because of varying load ? Link/node failures, network expansion... > Is this something a user-mode BIER utility > library, or a host stack, would > have to be involved with? If a BIER packet is created by an application level entity then it needs to insert the right bitstring, but as suggested above it might consult an external entity like a PCE controller or BIER-TE controller to get this information. Such interactions have not been defined yet. But likewise in normal BIER, you'd today need manual config or be able to retrieve IGP information to map from IP-address to BFR-id. > What portion of the bitmap would be needed for the "derived" bits? > > What is a reasonable ratio between true destination bits and > intermediate forwarding bits? See one of my last emails. Depends on how much traffic engineering you want/need. I think most deployment should be able to use less than 50% of bits. > How does this compare to using a TRILL-style encapsulation with the > outer-BIER header containing > *only* the forwarding bits and an inner BIER header containing only > the ultimate destination bits? Depends really on what you want to achieve. Easier to answer based on an explicit example if you have one... Cheers Toerless > _______________________________________________ > BIER mailing list > BIER@ietf.org > https://www.ietf.org/mailman/listinfo/bier
- [Bier] Questions on draft-eckert-bier-te-arch-01 Eric C Rosen
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Toerless Eckert
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Toerless Eckert
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Antoni Przygienda
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… IJsbrand Wijnands
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… IJsbrand Wijnands
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… IJsbrand Wijnands
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Antoni Przygienda
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Eric C Rosen
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Eric C Rosen
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Antoni Przygienda
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Antoni Przygienda
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Toerless Eckert
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Toerless Eckert
- [Bier] DISCUSS? SI vs. sub-domains - draft-ietf-b… Toerless Eckert
- Re: [Bier] DISCUSS? SI vs. sub-domains - draft-ie… Antoni Przygienda
- Re: [Bier] DISCUSS? SI vs. sub-domains - draft-ie… Caitlin Bestler
- Re: [Bier] DISCUSS? SI vs. sub-domains - draft-ie… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Eric C Rosen
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Toerless Eckert
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Caitlin Bestler
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Toerless Eckert
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Eric C Rosen
- Re: [Bier] Questions on draft-eckert-bier-te-arch… Toerless Eckert