redundancy [was: something about arrogance]

Tue Jul 30 10:02:12 UTC 2002


On Tue, 30 Jul 2002 03:23:24 -0700, Pedro R Marques wrote:

>All of those are much more frequent than the failure of an entire ISP (a
>transit provider). It is expected, i believe, of a competent ISP to
>provide redudancy both within a POP and intra-POP links/equipment and
>its connections to upstreams/peers.

	Yes, but when the ISP that all your redundant links go to and that you got 
all your IPs from goes out of business, what's the mean time to repair? 30 
days?

>So, my question to the list is, why is multi-homing to 2 different
>providers such a desirable thing ? What is the motivation and why is it
>prefered over multiple connections to the same upstream ?

	You cannot as easily be held hostage. I have consulted for a few ISPs and 
have my share of war stories.

	Here's a (true!) example. One day, a certain head of a fairly large ISP 
decided that he wouldn't route traffic to or from IPs he had assigned that 
didn't reverse resolve because he felt it was imperative that people be able 
to find network contacts in this way (I think he got sick of being the one to 
get the abuse emails). He told my client three days before implementing a 
sweep and filter. He had the equivalent of about 38 /24s from this ISP 
distributed over about 180 customers, they were his sole uplink.

	Here's another good one. A client needed a /22 immediately for a major 
customer about to come online, set it up fast or lost the account. We made 
sure to met all the IP assignment guidelines and our justification was 
impeccable, we had >90% utilization of a /18. The only problem was, the 
client's provider had a screw up in their allocations and justifications and 
their applications were being refused by ARIN until they fixed their 
problems. Now what?

	One more just for kicks. Client had a 100Mbps circuit from their sole 
provider (100Mbps to colocated router, DS3 from this router to their 
premises). The circuit had been in place for several years and the contract 
had long since expired. One day, they got a call -- they had 5 days to agree 
to a new (and MUCH higher) pricing scheme with a much higher minimum paid 
bandwidth amount or their circuit would be turned off. The kicker -- they had 
to agree to a two year term!

	The other issue is provider misconfigurations/meltdowns. They're not common, 
but if you're multihomed, you can just shut down the circuit to the 
misconfigured providers. There have been a few cases of these that I've seem 
where the repair time was several hours.

	If you add cases where just one POP was out, the number goes way up. If 
you're only in one location yourself and only use one provider, all of your 
redundant links will likely go to the same POP.

	DS