BGP Path Filtering

Sean Donelan sean at
Sat May 17 03:58:45 UTC 2003

On Fri, 16 May 2003, Joe Abley wrote:
> I don't think "start messy and clean up later" is good advice. Do it
> right the first time, and grow smoothly without difficult migrations.

I've found some people can make a mess with any tool you give them.  It
usually not a problem with the tool.

I don't suggest people use powerful tools just for ego gratification.
They should use the tool appropriate for the size of the job.  Don't
use a dynamic routing protocol when a static route will do.  Don't use
an exterior gateway protocol when you are connected to a single network.
Don't use dynamic route prefix tagging when a static filter will do.
Don't use route reflectors when a full mesh will do.  Don't use the
Openview network management suite, when MRTG will do.  Don't use a
GSR 12000, when a 2600 will do.

Each of those tools can be configured "cleanly." When your network
outgrows a particular tool, you need to transition to the next tool.
Of course, some people fail to transition at the appropriate time and
end up pushing a tool past its breaking point. I also don't suggest
people use lots of duct tape or Rube Goldberg contraptions on their
network.  As I said, there are times when there is a reason for using
community tagging in your network.

Are you suggesting that its a bad idea to make things appear "too easy,"
and by suggesting more complex configs we'll scare off the bottom rung
of network engineers.  Maybe.

Barry Greene's & Philip Smith's book "Cisco ISP Essentials: A
comprehensive guide to the best common practices for Internet service
providers" uses static prefix filters almost exclusively in all of its
example "best practices" for ISPs.  Although the ISP book is a useful
reference for network engineers at any size network, the examples
work best for networks of a certain size.

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