# Calculator written in route-map

Jennifer Rexford jrex at CS.Princeton.EDU
Tue Apr 1 15:22:08 UTC 2014

```Job,

Fun!  More generally, BGP has the same computing power as a Turing Machine:

Marco Chiesa, Luca Cittadini, Guiseppe Di Battista, Laurent Vanbever, and Stefano Vissicchio
Using routers to build logic circuits: How powerful is BGP? (ICNP'13)
http://vanbever.eu/pdfs/vanbever_turing_icnp_2013.pdf

-- Jen

On Apr 1, 2014, at 11:11 AM, Job Snijders <job at instituut.net> wrote:

> Hi all,
>
> Do you often find yourself in need of a simple calculator, and all you have
> available to you is a Brocade or Cisco IOS router?  No longer will you
> experience the horror and dread of mental arithmetics. The route-map calculator
> is here!
>
> Cisco IOS : http://instituut.net/~job/calculator-route-map.ioscisco.txt
>            (file size ~ 12 megabyte)
>
> In general I don't find route-maps useful to accomplish, well, anything.
> However, this is a striking example of re-usable configuration that has
> a measurable impact on daily operations!
>
> Calculations can be performed with integers between 1 and 256. The
> answer will be presented as a rounded positive integer. In case the
> calculation would result in a negative integer, larger than 2^16
> (65536), an helpful error message is generated: 65000:7777. For
> divisions and substractions the order of the BGP communities is
> relevant, one must always place the operator first!
>
> arithmetic operators:
>
>  'multiply' operator community:   65000:2
>  'substract' operator community:  65000:3
>  'divide' operator community:     65000:4
>
> example output:
>
>  telnet at input-router#show ip bgp routes detail 10.1.1.1 | i COMMUNITIES
>              COMMUNITIES: 65000:2 0:63 0:113    ! calculate 63 * 113
>  telnet at input-router#
>
>  telnet at calculator#show ip bgp routes detail 10.1.1.1 | i COMMUNITIES
>              COMMUNITIES: 0:7119                ! result: 7119
>  telnet at calculator#
>
> Super convenient right?!
>
> WARNING: due to IOS/Ironware architecture this route-map consumes quite
> some memory. Always test in a lab before deploying in production!
>
> Kind regards,
>
> Job
>

```