[j-nsp] full table?

[Keegan Holley]

2011/9/20 Pavel Lunin <plunin at senetsy.ru>

>
>  Is it always necessary to take in a full table?  Why or why not?  In light
>> of the Saudi Telekom fiasco I'm curious what others thing.  This question
>> is
>> understandably subjective.  We have datacenters with no more than three
>> upstreams.  We would obviously have to have a few copies of the table for
>> customers that want to receive it from us, but I'm curious if it is still
>> necessary to have a full table advertised from every peering.  Several
>> ISP's
>> will allow you to filter everything longer than say /20 and then receive a
>> default.  Just curious what others think and if anyone is doing this.
>>
>
> 1. If you have downstream ASes, than full table is [most probably] needed
> to be not just received but also used for forwarding (this is by default,
> but you can alter, see below). Otherwise loops/blackholes are possible in
> specific scenarios (split customer's AS, etc). Workarounds exist for this,
> but they are rather too complicated to maintain and make everyone in NOC to
> remember how it works. Some folks (especially DCs) don't care and just send
> full table to customers, not having it in data plane. For DCs with just few
> customers with their own ASes, this approach works well almost always (until
> something breaks). When issues arise, they troubleshot it and rewrite
> policies to accept additional routes. Not very good, but I saw this many
> times.
>

This is very insightful and probably the biggest hurdle to overcome.  I
definitely have downstreams that require the full table.  The combination of
full tables and skinny tables opens the possibility for routing loops,
suboptimal paths and confusion.  Then there's the NOC factor.

>
> 2. You must remember (people forget these basics surprisingly often), that
> full table, you receive from upstreams or IX-peer, is used to _send_
> traffic. So when you think it's useful to have full table to analyze or
> somehow intellectually influence traffic balancing across uplinks, you must
> remember that it only relates to traffic going _out_ your AS. Every couple
> of weeks I talk to someone who believes, he needs to receive full table,
> since he wants to "balance traffic". When I ask them, how much traffic they
> send out, it usually turns out to be not more than 10% of a single link
> capacity, and they don't experience any problem with it at all. And yes,
> most of them need to balance incoming traffic, but full table has nothing to
> do with this.
>

I often field this question myself.



>
> 6. If, after checking rules 1-5, you are still not sure if you need full
> table -- you definitely don't.
>

> Having this said, I'd say, full table is needed because of the downstream
> ASes. Playing the games described above does not worth it.


Wishful thinking I suppose.  Thanks all for humoring me.


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