nanog mailing list archives
Re: minimum IPv6 announcement size
From: William Herrin <bill () herrin us>
Date: Fri, 27 Sep 2013 16:10:23 -0400
On Fri, Sep 27, 2013 at 2:11 PM, William Herrin <bill () herrin us> wrote:
On Fri, Sep 27, 2013 at 1:04 PM, Randy Carpenter <rcarpen () network1 net> wrote:Therefore, I don't see any reason to artificially inflate the routing table by conserving, and then making orgs come back for additional allocations.I'm not convinced of that. Suppose the plan was: you start with a /56. When you need more you get a /48. Next is a /40. Next a /32. Next a /28. You can hold exactly one of each size, never more. And the RIRs tell us all which address banks each size comes from. In such a scenario, the RIR doesn't have to reserve a /28 for expansion every time the allocate a /32. 'Cause, you know, that's what they've been doing. And you can easily program your router to discard the TE routes you don't wish to carry since you know what the allocation size was. That means you only have to carry at most 5 routes for any given organization. You'd want to allow some TE for the sake of efficient routing, but you get to choose how much. As things stand now, you're going to allow those guys with the /19s and /22s to do traffic engineering all the way down to /48. You don't have a practical way to say "no."
Point is: there are a number of address management practices which significantly impact the routing table size. The ones that jump to mind are: 1. Receiving discontiguous blocks from the registry on subsequent requests. If the blocks can't aggregate then they consume two routes even if they don't need to. Registry-level mitigations: allocate in excess of immediate need. Reserve additional space to allow subsequent allocations by changing the netmask on the same contiguous block. 2. Registry assignments to single-homed users. Registry assignments can't aggregate, even if their use shares fate with another AS's routes. Registry-level mitigations:minimize allocations to organizations which are not multihomed. 3. Traffic engineering. Fine tuning how data flows by cutting up an address block into smaller announced routes. Registry-level mitigations: Standardize allocation sizes and allocate from blocks reserved for that particular allocation size. Do not change a netmask in order to reduce or enlarge an allocation. This allows the recipients of TE advertisements to identify them and, if desired, filter them. 4. ISP assignments to multihomed users. In other networks, assignments to end users from your space are likely to be indistinguishable from traffic engineering routes. TE filtering is impossible if some of the announcements are multihomed customers whose fate is not shared with the ISP to whom the space was allocated. Registry-level mitigations: Direct assignment to all multihomed networks. Discourage ISPs from assigning subnets to multihomed customers. Note the contradictory mitigations. Standardized block sizes increases the number of discontiguous blocks. Netmask changes defeat standardized block sizes. So, it's a balancing act. Does more route bloat come from filterable TE? Or from discontiguous allocations? The customer lock-in from being the organization who assigns the customer's IP addresses turns around and bites you in the form of unfilterable traffic engineering routes. Regards, Bill Herrin -- William D. Herrin ................ herrin () dirtside com bill () herrin us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004
Current thread:
- Re: minimum IPv6 announcement size, (continued)
- Re: minimum IPv6 announcement size joel jaeggli (Sep 26)
- Re: minimum IPv6 announcement size bmanning (Sep 26)
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- Re: minimum IPv6 announcement size Ryan McIntosh (Sep 27)
- Re: minimum IPv6 announcement size Brandon Ross (Sep 27)
- Re: minimum IPv6 announcement size Joe Abley (Sep 27)
- Re: minimum IPv6 announcement size William Herrin (Sep 27)
- Re: minimum IPv6 announcement size Randy Carpenter (Sep 27)
- Re: minimum IPv6 announcement size joel jaeggli (Sep 27)
- Re: minimum IPv6 announcement size Randy Carpenter (Sep 27)
- Re: minimum IPv6 announcement size William Herrin (Sep 27)
- Re: minimum IPv6 announcement size William Herrin (Sep 27)
- Re: minimum IPv6 announcement size Matt Palmer (Sep 27)
- Re: minimum IPv6 announcement size Owen DeLong (Sep 27)
- Re: minimum IPv6 announcement size Randy Bush (Sep 26)
- Re: minimum IPv6 announcement size William Herrin (Sep 30)
- Re: minimum IPv6 announcement size TJ (Sep 30)
- Re: minimum IPv6 announcement size William Herrin (Sep 30)
- Re: minimum IPv6 announcement size bmanning (Sep 30)
- Re: minimum IPv6 announcement size bmanning (Sep 26)
- Re: minimum IPv6 announcement size Ben (Sep 30)
- Fwd: minimum IPv6 announcement size Alexander Neilson (Sep 30)