BCP38 making it work, solving problems

Daniel Senie dts at senie.com
Tue Oct 12 02:50:44 UTC 2004

At 07:51 PM 10/11/2004, Richard A Steenbergen wrote:

>On Mon, Oct 11, 2004 at 06:03:08PM -0400, Daniel Senie wrote:
> >
> > I've removed the rest of your message, talking about which vendors do or
> > don't have what capabilities. While I agree it'd be nice if more vendors
> > offered automated tools for implementing ingress filtering, such tools are
> > unnecessary in most corporate network cases, thus the lack of corporate
> > customers asking for the feature. In reality every device offering access
> > control lists capable of filtering on source IP address can and does have
> > sufficient capability to implement BCP38.
> >
> > While I appreciate the desire to have a single switch solution, like was
> > possible with BCP34, it's a bit more complex to do in this case. It is,
> > however, disingenuous to say that devices don't support BCP38 because they
> > don't have an automated widget to implement it. Keep in mind that uRPF is
> > an implementation of BCP38 capability, and other implementations are
> > entirely possible.
> >
> > This was probably obvious to you, but others reading might find the
> > clarification useful.
>Yes if a box has source address packet filtering capabilities you can
>filter packets by source address ("Duh"). This doesn't mean that it is
>going to be sane or easy to implement the filtering by manually
>maintaining an acl of every prefix/host on every interface where you could
>have a customer or corporate box injecting spoofed packets into the
>network. I believe there are plenty of corporate networks out there that
>are far too complex to maintain with manual ACLs, I believe the reason
>that no one cares is simply because... no one cares. :)

One of your arguments presented was that corporate customers weren't asking 
for unicast RPF, and I responded that corporate customers are not in need 
of automated mechanisms to implement BCP38, since in most cases their 
networks are EDGE networks, and it's quite simple to filter your egress 
points to ensure you don't send out any spoofed packets.

You laid out a complaint against the equipment makers claiming they weren't 
implementing automated mechanisms BECAUSE the corporate customers were not 
asking for such tools, and I simply pointed out they shouldn't be expected 
to do so. If network operators need features, they need to ask for them 
when talking with potential vendors.

Network operators need to ensure downstreams don't advertise AS's they're 
not supposed to. Last I looked, that required some custom work (whether 
done by scripting or whatever, it's done off the router and pushed in). At 
the same time you're building those lists, you could be building ACLs. Some 
border routers will do this just fine, others won't. Next time you're 
qualifying routers for possible use, maybe the ability to handle wire speed 
acls might be worth testing?

>If you expect people to be able to maintain these filters on any scale,
>they need tools.

Why do those tools need to be built into the router? Are your tools for 
maintaining AS path filteirng built into the routers? Are the tools to 
archive and compare router configurations most of you use built into the 

>  Certainly uRPF is a good tool to do this, and certainly
>someone could implement some others that are different, but the complete
>lack of any tool, especially on the boxes where you should be doing this
>filtering, counts as a failure in my book.

I disagree that the tools must be an integral part of the router software. 
Perhaps it's time to think outside the (router) box?

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