Re: [Ila] [5gangip] ILA forwaring [Was Re: Problem Statement]

Dino Farinacci <> Tue, 01 May 2018 17:33 UTC

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From: Dino Farinacci <>
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Date: Tue, 01 May 2018 10:31:52 -0700
Cc: "Joel M. Halpern" <>,, Tom Herbert <>, 5GANGIP <>
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Subject: Re: [Ila] [5gangip] ILA forwaring [Was Re: Problem Statement]
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> I think you've misunderstood my position. Caches are _very_ important
> to eliminate the cost triangular routing (latency, average path load).
> This reduces latency and reduces average load on ILA-Rs. But, and this
> is the critical part, caches are only an _optimization_ in ILA. That
> means if the cache is rendered ineffective (like by a well crafted DOS
> attack) then the only effect is that the optimization is loss (i.e.
> greater latency due to triangular router)-- this is quantitively the
> worst effect of the attack on an ILA cache. This can be contrasted
> that to LISP where the worst case effects of a DOS attack on the cache
> is loss of service for users (infinite latency since packets can be
> dropped or indefinitely blocked on a cache miss).

Note in LISP, most of the time, prefixes are put in the cache. For ILA its mostly /128 host routes. And note, when an LISP ITR gets a Map-Reply, it can elect to put coarser EID-prefixes in the cache versus more specifics. Or, not elect to put anything in the cache and forward to PETRs (the same as your ILA-R routers) at the expense of suboptimal paths.

There are many options in LISP prevent DoS attack cache attacks. I don’t think that is true when caches are used in ILA.


> Tom
>> Yours,
>> Joel
>> On 5/1/18 12:37 PM, Tom Herbert wrote:
>>> On Tue, May 1, 2018 at 9:10 AM, Joel M. Halpern <>
>>> wrote:
>>>> Three reactions, all personal opinion (in case someone thinks my having
>>>> helped chair the BoF is in any way relevant; it isn't):
>>>> 1) If ILA-Ns do not have caches, the ILA-Rs will become hot-spots in the
>>>> network.  Yes, you have provision for multiple of them sharing load.
>>>> However, if that sharing gets to be a significant percentage of teh
>>>> routers
>>>> in the network, then there is no point in having bothered with ILA, you
>>>> are
>>>> just routing on the SIR.
>>> Joel,
>>> If you provision a network (or any system really) based on an
>>> assumption that caches will always attain some hit rate this is a
>>> fundamental mistake. One of the goals of a DOS attack would be to
>>> drive the hit rate to zero in which case someone will be in a world of
>>> hurt. Caches and DOS are a hard mix to contend with in nearly any
>>> context, that's why it's much better to view caches as an optimization
>>> rather than a requirement. They can be used to alleviate load, but
>>> that cannot be relied upon.
>>> I would also point out that caches only make sense as internal devices
>>> for intra domain communications. This does not make sense for edge
>>> routers that would need to create a working set cache for any
>>> aribtrary load of traffic from the Internet.
>>>> 2) As far as I can tell, when some ILA-N have caches, the ILA-R have no
>>>> way
>>>> of knowing whether the ILA-N have caches or not.  I can understand what
>>>> happens if all ILA-N in a network have the same cache state (either they
>>>> all
>>>> have caches or they all do not have caches).  But I do not know what
>>>> behavior you expect of an ILA-R if the ILA-N are not uniform. Given the
>>>> hot-spot issue above, I think you need to really explain why ILA-N would
>>>> not
>>>> ahve caches.
>>> ILA-Rs and ILA-Ns communicate via ILAMP protocol. That can include
>>> capabilities description.
>>>> 3 - Minor) Your usage of "sharding" seems odd.  You are simply dividing
>>>> the
>>>> domain into address blocks, and distributing responsibility for those
>>>> blocks
>>>> separately.  In other contexts, sharding seems to be used more generally
>>>> for
>>>> having subcollections of the data which can be moved around.
>>> Sharding is a database term that describes partitioning of the
>>> database into smaller chunks for manageablibilty. That is what is
>>> happening here (literally in the implementation since we are use a
>>> database backend).
>>> Tom
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