[AusNOG] Write up - Big ISP, little ISP, local internet exchanges
mmc at internode.com.au
Mon Sep 15 08:10:02 EST 2008
Edwin Groothuis wrote:
> The solution is a pure technical one: adjust the network to
> reflectwhat you are offering. Or say you are offering. Or what you
> said you were going to be offering.
Ultimately all we're looking for is a way of communicating a single bit
of information as meta data along with each packet. All we need to
know is "did this packet enter our network on a transit or peering
interface?". If a packet enters via a peering point then it shouldn't
leave via peering or transit. If a packet enters via transit it
shouldn't leave via a transit or peering port.
So, you could, assuming your network is MPLS enabled use the MPLS TE
bits (assuming you're not using them for QoS - even if you are I reckon
you probably aren't using all 3 bits). If a packet enters via peering
or transit, set a bit. On exit at a peering or transit bit, use a
policy map or your partitcular router vendor's mechanism to enforce
this. You could also mangle the packets and use the DSCP/ToS bits if
you don't mind doing that.
The great thing about this solution is it doesn't require updating any
filters or creating a whole lot of tunnels or wierd things. It should
be a set and forget on just the external interfaces.
Maybe it's possible to do something more clever with MPLS - maybe
prevent various label paths existing would also prevent the packets even
having to be carried.
A whole lot of our networking issues would probably be a lot easier if
we could carry some meta data with packets and have it interact with the
forwarding policy. I guess TE bits are an example, but a more generic
version would be nice.
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