Re: routing between provider edge and CPE routers

[Serge Maskalik]

 My recommendation would be for you to: 

   o redistribute directly connected interfaces via a strict
 filter into BGP and use iBGP to carry it around the local
 AS 

or 

   o use passive interfaces in IGPs to do the same

 Avoid having to run a topology computation everytime a T1/56k 
 links drops. I prefer the first option to the second based on 
 experience UUNET / Global Crossing has w/ option #1. 

- Serge

Thus spake Mike Bernico ([EMAIL PROTECTED]):

> 
> 
> Hi,
> 
> I apologize if this has been asked before.  I work for an ISP that
> started very small (hundreds of T1 and 56k customers) and has grown very
> large in the last few years (thousands of T1 customers, as well as DS3
> customers and OC3 customers).  
> 
> We currently use an IGP to route between our distribution routers and
> the CPE routers we manage.  This has historically worked very well. We
> have recently begun running into scalability issues however.  We have
> some distribution routers that have over 1000 T1 interfaces on them.
> This is causing some problems with stability in that edge IGP.  Does any
> other service provider use an IGP all the way to the customer for non
> BGP customers or are we the only one?  I have a feeling we maybe are.  
> 
> If you do use an IGP, have you had any of the scalability issues we have
> had?  How did you fix them?
> 
> If you use statics/BGP to CPE routers have you had any issues doing
> that?  In particular I'm wondering about the thousands of lines of
> configuration used to make static routes work.  
> 
> 
> Thanks in advance for your advice.
> 
> Mike Bernico

Re: Aggregate traffic management

[Serge Maskalik]

   Stanislav, 

  It depends what control mechanism you are using: 

   o routes learned via an IGP - ECMP would work and if it's a single 
 destination host, per-packet loadbalancing between the outgoing 
 links is your only practical choice; rest of ECMP schemes work 
 by distributing flows or routes amongst links

   o learned via BGP and the traffic consists of a variety of flows 
 that all use the same reachability information (BGP route); you 
 could de-aggregate the announcement locally if you have an idea 
 how the per-flow volume maps into the route; BGP Multipath feature
 set exists in most router implementations, but the distribution 
 methods are statistically different

  For the latter, several systems exist in the market place that try 
  to automate TE for BGP-learned routes, one of which is ours. These 
  system require a closed feedback loop for traffic volume per flow 
  and link mappings; this needs to occur close to real time to be 
  effective. 
  
- Serge  

Thus spake Stanislav Rost ([EMAIL PROTECTED]):

> 
> Dear NANOGers,
> 
> I have a very hands-on question:
> Suppose I am a network operator for a decent-sized ISP, and I decide
> that I want to "divide" aggregate traffic flowing through a router
> toward some destination, in order to then send some of it through one
> route and the remainder through another route.  Thus, I desire to
> enforce some traffic engineering decision.
> 
> How would I be able to accomplish this "division"?  What technologies
> (even if vendor-specific) would I use?  
> 
> I can think of some methods like prefix-matching classification and
> ECMP, but I am still not sure exactly how the latter works in practice
> (at the router level) and how one may set them up to achieve such
> load-sharing.
> 
> Thank you for your expertise and lore,
> 
> -- 
> Stanislav Rost <[EMAIL PROTECTED]>
> Laboratory for Computer Science, MIT