[c-nsp] T3 or Ethernet delivery?

[Jon Lewis]

On Wed, 8 Apr 2009, Jeffrey Ollie wrote:

>> How do you detect a "down" condition on Ethernet? My experience is that
>> the interface could be up/up because Ethernet doesn't know about
>> anything further down the line and ends up throwing packets into a
>> magical black hole. Or worse, secret packet loss.
>
> There's nothing unique to Ethernet about that...

No, but with ethernet, it's more likely that there's going to be a layer 2 
"local device" (i.e. a switch) which you connect to, but the layer 3 next 
hop is somewhere off on the providers network in another building.  When 
the network breaks somewhere between the provider's L3 next hop and your 
location, you'll still be up/up, but have no connectivity.  With BGP, you 
might tune the timers shorter than default so that such a break gets 
noticed sooner.  With a T3, BGP would find out about the break as soon as 
the interface went down.

With ethernet, it's also somewhat easier for your provider to screw things 
up.  I've dealt with several instances where a carrier managed to combine 
multiple customer VLANs and mix traffic to/from unrelated customers.  I've 
seen similar things once on a DS3 though, so it's not impossible 
there...just much less likely.

Ethernet is generally much cheaper for interfaces.

----------------------------------------------------------------------
  Jon Lewis                   |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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