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Re: Latest estimate: Internet Routing table / Memory needed

  • From: Alan Hannan
  • Date: Fri Mar 26 21:33:00 1999

  hi Brandon,

  i'm not sure I can a whole lot of value here, but that doesn't
  seem to stop most people posting to [email protected], so I'll add

  you are correct in your assertion that additional views (where
  view is defined as a table learned from a unique provider) will
  increase the amount of memory required to hold the bgp table.

  but this is only one component of size.

  Without thinking too much, the following is a list of variables
  which can/will influence bgp memory requirements:

  	. number of routes leared from each provider
	. number of unique routes in the routers' view of the internet
	. number of as-paths in the backbone table
	. number of peering sessions, esp. as a function of
	   the peer's routes
	   	- ie - a small peer offers less than a large peer
		- transit provider BGP feeds should be similar in 
		  size and distribution, though not exactly the
		  same, as one's perception of the internet varies
		  based upon the vantage point

	there are neat tricks that bgp programmers do, like storing
	as paths in patricia/radix trees, and referencing the
	as-path from the routes array, etc..

  additionally, on a feature/vendor basis, the following will
  also impact memory requirements:

  	. soft reconfiguration in and out
	. policy instantiations
	. dampening history and policy

  from an fgc perspective, we see gross memory utilization similar
  to yours.

  from a mae-west router w/ approximately 50 peers, we see, on a
  cisco 75xx:

|	61341 network entries and 181983 paths using 11650851 bytes of memory
|	20707 BGP path attribute entries using 2587116 bytes of memory
|	91295 BGP route-map cache entries using 1460720 bytes of memory
|	5670 BGP filter-list cache entries using 90720 bytes of memory
|	Dampening enabled. 380 history paths, 25 dampened paths
|	10553 received paths for inbound soft reconfiguration
|	BGP activity 153132/91791 prefixes, 2990192/2808209 paths
|	1762451 prefixes revised.

  hope this perspective helps.


Thus spake Brandon Applegate ([email protected])
 on or about Fri, Mar 26, 1999 at 03:54:02PM -0500:
> I haven't really seen anything on this in a while, in terms of an up to
> date figure.  Here is what our internet border router reports (with full
> from UUnet and Digex, and a few more (^3561$) directly from CW):
> 58909 network entries (116785/119858 paths) using 10448216 bytes of memory
> 15451 BGP path attribute entries using 1946036 bytes of memory
> 0 BGP route-map cache entries using 0 bytes of memory
> 2 BGP filter-list cache entries using 32 bytes of memory
> Looks like I'm burning about 12 megs.  Lets say I had the whole table (~
> 58/59k networks today), but only one provider.  Rather than turning half
> our Internet feed off to see, could someone tell me how this would affect
> the above 'sh ip bgp summ' result from my router ??  I.e. how much memory
> would be burnt then ??
> Thanks in advance...
> --------------------------------------------------
> Brandon Applegate, CCNA  :  Network Administrator
>       :  [email protected]
> --------------------------------------------------