North American Network Operators Group|
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Hello, Having watched the 'route filtering panel' discussion from the most recent NANOG meeting, I have an idea which I would like to float. One of the concerns raised was that small ISPs are not eligible for provider-independent blocks; unfortunately this forces them to renumber if they change upstream provider. It was pointed out that this in itself is not a good reason for getting PI space, because then everybody would want it. Now, renumbering is tedious but in principle not difficult. The major difficulties are with DNS - in particular, changing the DNS settings in all the clients, which may well have the IP addresses of the ISP's caching nameservers hardcoded in.  My suggestion is that a small amount of unrouted space is allocated for "provider-local" use. For sake of example, let's say 200.0.0/24. Then we can assign say 184.108.40.206 and 220.127.116.11 as well-known addresses for local primary and secondary DNS caches. These are configured as loopback interfaces on the ISP's DNS servers, and static /32 routes injected into the provider's IGP to reach them.  The ISP would not need to divulge the 'real' addresses of its DNS caches, and could thus renumber at will. It would also benefit customers who roam between multiple ISPs, as they wouldn't have to keep changing their client settings. Notice it should work for multiple levels of service-provider hierarchy: sending a packet to 18.104.22.168 would follow defaultroute until it hit the first ISP who implements a server on this address. These addresses might be useful for other services too: e.g. outgoing SMTP relays, NTP servers, etc. In principle all these should have DNS names which customers use, but experience shows that customers _do_ end up hardcoding IP addresses into their configurations, which makes it very difficult to renumber them. The allocation would only need to be a single /24 or smaller, and it could come from any useless bit of 'toxic waste' because it would not actually be routed on the Internet. Does anybody see any value in this proposal? Of course, it's not much help to an ISP with downstream leased-line customers, because the customers will have to renumber as well. Regards, Brian Candler. [this posting is from my personal address and not on behalf of my employer]  There are MS extensions to PPP to negotiate primary/secondary DNS cache, but not everybody uses them.  We can also preallocate space in a way suitable for subnetting: 22.214.171.124 Primary DNS cache 126.96.36.199 Primary NTP server ... 188.8.131.52 Secondary DNS cache 184.108.40.206 Secondary NTP server ... This allows people to implement this proposal by bringing up interface aliases, without messing with host routes in IGP, and still have some resilience by putting the primary/secondary services on different physical networks.