aads renumbering rumor and implications

Alex Bligh amb at gxn.net
Mon Jan 25 00:13:28 UTC 1999

Randy et al.,
> should this be true and  a real issue,
>   o will folk be happy renumbering at larger exchanges?

There have been some recent presentations by LINX over their renumbering
exercise. I guess there were about 60 members and perhaps 80-90 routers
at the time, but the presentation would be more accurate. Essentially
it was smooth. The main problems (from my POV) were caused by one minor
Cisco bizarreness on BGP router ID, by people reading /23 as /24,
and by people not disabling gacky things such as proxy ARP and other
spawn-of-the-devil type things which AADS, not been MAC based, will
not suffer from.

>   o does anyone see why the exchange address space needs to be globally
>     routable?

Aids debugging (i.e. traceroutes will always give reverse DNS, and every
hop should be reachable somehow; possible to IP source-route for
traceroute -g to the address etc.). I thought the advantages and disadvantages
of reachability of IXP DMZ have been pretty extensively covered,
and the consensus should be:
1. IXPs should set some policy on who should advertise their DMZ, and
   other people should not.
2. ISPs should be wary of accepting IXP DMZ advertisements, or
   more specifics thereof. An obvious way to do this is (for Cisco
   speakers) to set next-hop-self in their IBGP mesh and not introduce the
   DMZ into either the IGP or into iBGP, instead carrying the exit address
   as the loopback interface of the connected router throughout.

More to the point, if you take it as a necessity that people configure
routers on IXPs sensibly for all sorts of other reasons, does anyone
see why the IXP address space should *not* be globally routable? ATM
NAPS such as AADS are better protected against the abuses such as
GRE to IXP connected routers (i.e. the PVC must preexist) than most
common-access exchanges.

My take on the LINX exercise was merely that those who suffered
in some way did so *in general* due to their own cluelessness.
Everything that happened *due solely to renumbering* which caused
anyone else pain would have have been discovered at some point anyhow.

Your router load may vary, of course.

Alex Bligh
GX Networks (formerly Xara Networks)

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