North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: Emergency backup for a small net
At 09:04 AM 5/18/97 -0400, Bradley Dunn wrote: This brings up a problem I have been trying to solve for a while that I have not found an answer to. A company with an old style Class B (/16) wants to be multihomed and split their incoming load between 2 ISPs (outgoing they can live with going via 1 and if the primary fails they fallback to the secondary conenction). In order to split the load on incoming, one ISP has to announce a /17 and the other ISP has to announce a /17 (or even the entire /16). But since this net is from the 147.x.x.x range, various ISPs around the globe will filter out the /17. This means that having a /16 from the 192.x.x.x range is better (these days), unless someone can show me a solution. Thanks, Hank >Hi, > >We have a small ISP customer that wants to run a circuit to another local >ISP and the ISPs would use that pipe only in the case of primary link >failure. The two ISPs would split the cost, etc. > >The obvious solution would be for both ISPs to set up BGP peering with >their upstreams and not announce anything in normal operation. The >upstreams would continue to statically route the smaller ISPs' blocks and >the smaller ISPs would default to their upstreams. The smaller ISPs would >also put in a default pointing at each other with a higher cost. Then in >the case of primary link failure the ISP who still has a path to the net >would begin announcing the other ISP's block(s) to their upstream. The >upstream would in turn see this as a valid announcement and propagate it >to the world. Therefore specificity should draw all the traffic to the >correct place. > >The problem is both ISPs are small and have /24s from their providers. The >/24s would be filtered by many, leading to only partial connectivity in >the case of failure. (Partial connectivity is better than no connectivity, >I guess...) > >Another possible solution I thought of is to use NAT. The small ISPs would >use RFC1918 internally and use a block from their provider to translate >into. When the primary link fails they switch over to using a block from >the other ISP's provider. They would also have to use very low TTLs for >their DNS zones and be prepared to switch the DNS zones to point to the >other block. Does the NIC consider this efficient utilization >to have a block lying around that only gets used when a link fails? > >An important thing to remember here is that the backup link will not be >used in normal operation. This is not multihoming. They do not want load >balancing. > >I would be interested to hear others' thoughts on this. If you reply >privately I will summarize any interesting replies to the list. > >Thanks! > >pbd >-- >You can make it illegal, but you can't make it unpopular. > > - - - - - - - - - - - - - - - - -
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