routing table go boom

Wed Mar 20 11:42:26 UTC 2013

Hi Masataka,

On 20 Mar. 2013, at 00:23 , Masataka Ohta <mohta at necom830.hpcl.titech.ac.jp> wrote:

> David Conrad wrote:
> 
>> One of the advantages I see in LISP(-like) solutions is that it
>> allows multi-homing without having to do BGP...
> 
> By having a lot larger table than BGP.
> 
> http://datatracker.ietf.org/doc/draft-ietf-lisp-architecture/?include_text=1
> 
>   It should be noted that the caching spoken of here is likely not
>   classic caching, where there is a fixed/limited size cache, and
>   entries have to be discarded to make room for newly needed entries.
>   The economics of memory being what they are, there is no reason to
>   discard mappings once they have been loaded (although of course
>   implementations are free to chose to do so, if they wish to).

LISP will not have huge caches:

(1) http://www.ietf.org/proceedings/69/slides/RRG-4.pdf

and more recently:

(2) https://www.net.t-labs.tu-berlin.de/papers/KIF-ADDITLCAWISKAI-11.pdf

> 
> Worse, the table is updated so frequently.
> 

FIrst of all the table a cache is filled on-demand, so you update only what you need, secondly (1) shows that this refresh traffic is in the same order of magnitude of DNS requests. If you are able to support DNS you are able to deal with LISP cache update traffic.

> http://datatracker.ietf.org/doc/draft-ietf-lisp-introduction/?include_text=1
> 
>   A node may have more than one
>   RLOC, or its RLOC may change over time (e.g. if the node is mobile),
>   but it keeps the same EID.
> 
> Assuming that there are 4G mobile devices in the world, the
> mapping table has more than 4G entries each updated every
> minute or second.

This is true in a push model like BGP not in LISP, which is a pull model (on-demand).

> 
> The problem of LISP is that it breaks the end to end principle
> to introduce intelligent intermediate entities of ITR and ETR.

true

> 
> Mobility can best be handled end to end by end systems of MN,
> HA and, optionally, CN.
> 

which rely on intelligent anchor nodes spread in the network, where is the difference? 

Luigi

> 						Masataka Ohta
> 
> PS
> 
> Considering that the Internet is connectionless because all the
> routers have routing tables covering all the IP addresses in
> realtime, LISP won't be operational unless most of routers
> in DFZ have full mapping table in realtime.
> 