Date: Sun, 18 Mar 2012 16:09:31 +0000
From: James Condron <james@...o-internet.org.uk>
To: Valdis.Kletnieks@...edu
Cc: full-disclosure@...ts.grok.org.uk
Subject: Re: is my ISP lying or stupid?

 Sorry, I don't mean to be rude but none of that made any sense, especially from an ISP perspective.

You will never have a switch per area; it doesn't work like that, you'll have a series of distribution routers for routing to customers. Mail, www, shell, SIP, whatever will be other services which of course are on one to a milloin switches.  Really doesn't matter as this has nothing to do with anything.

The routers of an ISP are sorta DHCP in the sense that the IPs are dynamic- DHCP really works as one network whereas an ISP switch will have a series of /30 vlans for obvious reasons. Getting an IP and connection is more complex than that but already we're down to a series of routers.

Somewhere in a datacenter (Lets keep it simple for now) is a cabinet with a bunch of servers in; one will do customer web space and so on. This cabinet will have a switch in and either this went or the router it is connected to.

They're not using teaming. They're not using loadbalancers. 17^39 is a bit of a weird one to even have to type out.

Somewhere someone pulled the wrong cable or someone broke a route. These are the two things which cause (In my experience) almost all of ISP issues. That or a switch died.

And whether they meant switch or not they said switch. Chances are they lost a blade or an SFP or whatever.

On 18 Mar 2012, at 15:47, Valdis.Kletnieks@...edu wrote:

> On Sun, 18 Mar 2012 12:49:49 -0000, Peter Maxwell said:
>> On 16 March 2012 19:11, Dave <iryshman@...il.com> wrote:
>>> Your ISP probably has their users are on different networks than their
>>> servers.  Sounds like maybe they meant the switch you are on, not the
>>> servers switch.  Need to troubleshoot, use a smart phone or some other OOB
>>> capable device to test access to the ISP servers.  If you can access OOB,
>>> then maybe they aren't lying.  Just a guess, you didnt provide much detail.
> 
>> Unlikely, usually these switches are quite large and when a user has OOB it
>> usually means console access to the server, i.e. nothing to do with network
>> topology.
> 
> I strongly suspect that what Dave meant was:
> 
> 1) There's a switch at the ISP's central site that the services live on.
> 2) There's *another* switch that you and the other subscribers in your
> area are connected to.
> 3) If you can reach the mail server via other means (IP-capable cellphone,
> wireless from the local McDonalds, etc), it's more likely switch (2) than (1).
> 
> The real troubleshooting fun starts when you throw things like load balancers
> and ethernet bonding into the the config.  Nice things if they work, but can be
> a bear to diagnose.  If they're doing round-robin, they can end up hosing every
> N'th connection (which is loads of fun when N is in the hundreds).  The other
> common failure mode is hashing each inbound's address to determine which back
> end to go to and certain hash values end up in the bit bucket - so it all works
> great unless your DHCP-supplied IP address is (when treated as a 32-bit number)
> equal to 17 mod 39 or some siimilarl wierdness.  The troubleshooting fun gets
> even worse if the hash contains both the IP and the ephemeral port number - this
> can result in intermittent issues that will take *month* to find and diagnose, because
> most users will just hit reload, and since the ephemeral port on their end changed,
> it works for them and they never report it...
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
> Hosted and sponsored by Secunia - http://secunia.com/

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/

Powered by blists - more mailing lists