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Question about mulitple connections
| Posted by mchosted, 12-24-2002, 07:58 PM |
| If a data center is suppose to have mulitple or redundant connections to the internet, then why would a problem with just one of those connections result in down time? Shouldn't one of the other connections take the place of the connection having problems?
Thanks
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| Posted by TheTech, 12-25-2002, 12:05 AM |
| Good question mchosted, I'd like to know that myself..
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| Posted by Luxore, 12-25-2002, 02:35 AM |
| suppose you are a host and you are sitting in some wonderful carrier neutral datacenter surrounded by 50 connectivity providers.
and let's say that you buy a connection from cogent, cause it's really reasonably priced. so cogent gives you a link, and some IP addresses from a block of addresses that arin gave them to use.
you are single homed
traffic finds you because other networks listen to cogent's bgp routing announcements about those blocks of IPs.
traffic finds it's way out from you to other people by you having a default route to a machine on cogent's network.
so you do some advertising and visit webhosting talk and get some customers and pretty soon you have about 500 ip addresses from cogent all in use on your box.
and you like what you are doing, but you don't like all the trash talk about cogent so you decide you need another connection.
so now you talk to williams and buy a line from them. they give you some IPs to use from a larger block that arin gave them. they make bgp announcements of their blocks.
you have redundant connections.
traffic now reaches inbound on both lines. traffic for the cogent addresses comes in on their line. traffic for the williams addresses comes in that their line.
how does traffic get out?
that's up to you. you can dump it one way, or the other way, or split it up.
a month ago most people would send it to cogent because that would have been decent connectivity and usually cost less than the williams. this week aol users have trouble reaching cogent, so lots of people would send aol traffic to williams and the rest to cogent
so are you multi-homed?
technically yes, but not really.
you are using addresses which belong to your upstreams. you do not yourself run bgp and announce these addresses. even if you did run bgp and announce the addresses, it is likely that most people in the world would not hear those routing announcements because your address blocks are so small. they would be filtered from the global routing tables by someone like, oh, let's say sprint.
so if one of your connections went completely down, people out in the big world would not know that they could reach YOUR block of cogent addresses through your williams connection, or your williams addresses through your cogent connection.
So no incoming page requests would reach the server for sites using ip addresses from the provider whose link was down. which means no outgoing pages would reach anyone. ack! sites are down! you've got mail!
you as a company are multi-homed, but your individual customers are not.
you can be really clever and do name based hosting and make sure that every virtual server has an ip from each provider and make multiple nameserver on each network.
but it starts getting messy, both technically and ethically.
Last edited by Luxore; 12-25-2002 at 02:42 AM.
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| Posted by mchosted, 12-25-2002, 05:03 AM |
| wow....thanks for the info... not sure I understand it all, but thanks... sounds like everything is set up all wrong... internet community needs to get their act together and make some changes
So basically the way it is set up, it does little good to have multiple connections from the data center to the internet?
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| Posted by Luxore, 12-25-2002, 02:43 PM |
| Multiple connections can be much better, but they aren't ALWAYS much better.
Sometimes they are only a little better. Sometimes they are quite a bit better.
I guess mostly what I'm saying is that it's easy to be misled when a sales blurb gives you only part of the story and you don't ask enough questions to find out the rest of the story.
I could say more about this, and maybe I will, but I have to go do a bit of Christmas now
Merry merry!
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| Posted by virtualdennis, 12-25-2002, 11:51 PM |
| A properly designed multi-homed network can do exactly what most want- failover or find an alternate path if the primary path goes down or is saturated with traffic..
However is most hosts/ISP's like this? No.. Why? Because its expensive for the hardware/software to implement this properly. If they designed their network correctly and have paid out the cash to implement it properly, the result would be exactly what you're talking about..
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