[Sysadmins] DSL -v- Leased Lines

Nick Hilliard nick at netability.ie
Sat Nov 14 22:11:15 GMT 2009


On 14/11/2009 13:05, Harry Duncan wrote:
> Curious to hear thoughts...

For my office ip connectivity, I use multiple DSL accounts with a Cisco 
1800 router with some funky configuration in it to do load-balancing and 
automatic failover between the two.  It has well quantified failure modes, 
but in general provides good quality desktop access to my office users, and 
when both lines are up (they almost always are), I can route just voip 
traffic over one line.

A leased line connection would probably be more reliable, yes.  They also 
have better SLAs if you're interested in ass-covering (although I'm more 
interested in actual reliability than legal ass-covering).  There's also 
the option of using SDSL.

If I had a serious interest in site-to-site connectivity, I would consider 
the following options:

- multiple broadband links at each end, using two selected providers.  This 
will allow you to set up one vpn per provider between each host; you can 
load balance or whatever using ospf / eigrp / whatever routing protocol, 
and this will provide automatic failover.  advantages: cheap. 
disadvantages: getting router configuration working and stable is 
complicated; high latency on DSL (particularly if blocking is used on any 
link); maxes out at 1M connectivity due to asymmetric nature of most 
consumer broadband products (although not Imagine Breeze).

- leased line: advantages: good SLA, complication level is small. 
Disadvantages: slow speed, very expensive per megabit, SLA may not mean a 
whole lot in reality, although they are quantitatively more reliable than 
dsl links.

- service provider vpn: several options here; service providers can prove 
end tail using SDSL/EFM or local leased lines, and tunnel over the 
backbones using a variety of technologies (mpls, other vpn, etc).  If 
you've got enough sites to make it feasible, some providers will even do 
stuff like creating private DSL login groups, so when you log in over DSL, 
you get connected into your own backbone cloud, which has controlled or no 
connectivity to the rest of the internet.  advantages: flexible service can 
be provided by various providers; disadvantages: expensive, can be 
complicated, depending on what you're trying to do.

- fibre: advantages: excellent reliability (and if you have a diversely 
routed ring, almost guaranteed reliability), arbitrarily high speeds. 
disadvantages: is extremely expensive (and imho unnecessarily, as most 
ducts are very sparsely populated), particularly if there's a dig involved.

So, really the question is: how much is this worth to you?  If you want to 
do cheap and cheerful, get a cisco 1800 router, an Imagine Breeze 4Mb or 
6Mb link, with a backup DSL connection from an LLU provider (or cable from 
UPC) and do your fancy inter-site VPN connectivity using this.  If your 
management cares about SLAs, and is prepared to spend more money, get 
something more expensive, as the reliability level is generally higher, and 
there is a lot more legal recourse if something goes wrong.  If you have 
€∞, get fibre.  It's just wonderful.

[As an unrelated side thought, I was working out the other day how much it 
would cost for a 10G connection from dub->ams based on the costs that EUnet 
Ireland was paying for 64k in ~1995.  I figure a little under €1 billion 
per annum, based on the same cost per meg per month.]

Nick



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