SDSL vs 8 mb ADSL
Paul Welsh
connections.
For web browsing our users connect via an 8 mb (Max Premium?) ADSL line
which tends to be capable of 4 to 5 mb download speeds.
If the leased line should fail the idea is that the incoming
connections to the web site can be routed (DNS failover) via the ADSL
connection which is in theory capable of 832 kb.
Our monthly ADSL usage varies considerably - between 15 gb and 30 gb in
the last 3 months.
I'd feel happier with a 2 mb SDSL circuit as a backup to the leased
line. Do you think the web browsing speeds would be noticeably worse
with an SDSL service?
Any recommendations? I was thinking about Eclipse.
Keith Wassell
freedom to surf, and gave us uploads in the region of 180k/s twice that
of your MAX ADSL. Only thing was as SDSL is so rare, no one could be
got out to fix it quickly if it went over. unless we paid a ransom in
extra care payments, we were going to be off for 7+ days every time it
went over. after the second event in 6 months, we ceased it and rented
a dedicated server from Pipex. Cheaper too and peace of mind
Regards, Keith ( who thinks SDSL is *** SERIOUSLY *** overpriced !!!)
Spack
DNS failover isn't a great backup solution - in order for it to work you
have to use really low caching times, which means that you then increase the
DNS traffic. If you use longer caching times then when you have a failure
some customers may not be able to get to your servers due to their ISP or
local DNS caches still having the address that is no longer working.
We're using Easynet 2Mbps SDSL here and it's great, it actually feels faster
than the 2Mbps ADSL I have at home (I'm on MaxDSL now but due to congestion
at the exchange I'm still only getting 2Mbps instead of the BRAS value of
5500kbps). We used to have a 2Mbps leased line, the SDSL has been just as
reliable and a lot cheaper. We've currently got only ISDN backup on it, but
we're looking at moving this to ADSL or SDSL (both options are quite
expensive unfortunately) - the advantage this has over DNS failover is that
we can keep our DNS TTLs high to keep DNS traffic low, and re-routing to the
backup line is done by the ISP so our IP addresses don't change and the
process is transparent from the customer point of view (albeit somewhat
slower over ISDN, but it's better than nothing). The other option I'm
looking at is co-location, up till recently it wasn't possible for us to do
this but it's now a definite contender, and means that local connection
problems will only cause small delays in order processing rather than
potential loss of customers, and our sites would be on a much faster
connection.
Dan
Muxton
We do a very popular 2Mbps leased line with ADSL/SDSL failover that
*isn't* dependent on DNS changes, it's done with OSPF, so you don't
have to faff around with fiddly changeovers. The whole lot probably
costs less than your leased line alone :-) You don't have to make any
phyiscal changes either as it's all presented to you as Ethernet on
one router, all you have to do is plug your firewall in.
Drop me a line, jake dot perks at entagroup dot com, if it's of
interest.
Jake
--
Address munged but valid - remove mungbeans.
NoNeedToKnow
>when you have a failure some customers may not be able to get to your
>servers due to their ISP or local DNS caches still having the address
>that is no longer working.
Although I'm not a customer, it might be worth mentioning AAISP (aa.nu)
which has certainly offered a backup connection (in the past) where the
backup would get the same fixed IP as the "main" connection. SDSL might
be very expensive, however, but if they offered SDSL as first link and a
DSL Max Premium as the backup (so not usually available, of course) the
cost might be low enought to be considered, and it shouldn't have many
of the DNS change/cache problems that might otherwise be the case.
It was on their old price list (still worth checking, I'd have thought,
to see if they can offer an Office Max as a backup):
Extra line £20.00 £23.50 - 2M/250K
Additional office grade circuits at the same site on the same base login.
http://aa.nu/aa/aaisp/oldprices.html
I'm assuming the "same base login" means this 'extra line' would be given
the same IP (and of course only one connection could be active at a time,
so they'd route the traffic to/from whichever of them was 'live'). They
also have a unit called the Firebrick which I think will handle two WAN
connections and switch as needed :-) (NB Firebrick is not cheap!)
Paul Welsh
Spack wrote:
> DNS failover isn't a great backup solution - in order for it to work you
> have to use really low caching times, which means that you then increase the
> DNS traffic. If you use longer caching times then when you have a failure
> some customers may not be able to get to your servers due to their ISP or
> local DNS caches still having the address that is no longer working.
>
> We're using Easynet 2Mbps SDSL here and it's great, it actually feels faster
> than the 2Mbps ADSL I have at home (I'm on MaxDSL now but due to congestion
> at the exchange I'm still only getting 2Mbps instead of the BRAS value of
> 5500kbps). We used to have a 2Mbps leased line, the SDSL has been just as
> reliable and a lot cheaper. We've currently got only ISDN backup on it, but
> we're looking at moving this to ADSL or SDSL
Points taken but we'd use a third party to provide the DNS failover so
low TTLs not really an issue. I considered Easynet but quite honestly
we were going from a v. expensive leased line from UUNET / MCI and so
the BT leased line we now have represented a substantial saving (they
do various special offers etc). Easynet was cheaper still but since we
already had fibre it seemed a shame to waste it.
The advantage with having 2 separate lines and IP address ranges is
that usually connectivity problems arise because of routing issues with
the ISP. The service degrades rather than stops. Having 2 independent
connections with different ISPs helps get around this issue.