[j-nsp] BGP route-reflection question

Hannes Gredler hannes at juniper.net
Thu May 29 20:45:59 EDT 2003

On Thu, May 29, 2003 at 09:14:18AM -0600, Danny McPherson wrote:
| On 5/29/03 2:18 AM, "Hannes Gredler" <hannes at juniper.net> wrote:
| > most of the BGP scaling properties are bound to memory size, you are right:
| > 
| > however, what i fail to see is why path diversity is negatively impacting
| > convergence;
| > what i have seen to far is contrary: a healthy path diversity speeds
| > up convergence; 
| I think you're confusing the issue, what new diversity do you get that
| simple loopback peering wouldn't provide?   The transmission substrate
| doesn't change, you're simply adding lots of overhead unnecessarily,
| subsequently effecting convergence, memory consumption and CPU utilization,
| in _any router.

no doubt simple loopback peering inside the lcuster does do the trick;
however from an administration point of view, SPs in my theatre here,
try to avoid the intracluster full mesh and better
go with diverse cluster IDs in the same RR level; 
| > of course many paths do cost memory; so the main challenge
| > is to convince "the other vendor" to ship proper memory with their boxes and
| > not to tweak the design of the routing mesh to the limitations of a single
| > implementation;
| It's not just about memory, or any particular vendor.  Although memory is
| one factor (in which case by following your recommendation you'll(J) use
| more as well, no?), it's also about the protocol capabilities.  If you send
| 2x or 3x the amount of updates because they can't be packed as efficiently
| that effects the entire routing system -- not just a single box -- although
| every individual box is effected as well.  If receivers now have to pack and
| process twice as many updates, or aggregate Adj-RIBs-In are much larger,
| that eventually effects the characteristics of the entire routing system.

indeed it is; you are assumming that it is double the amount of processing load,
however that entirely depends on the implementation; i.e. how the system internally
maintains its path and prefix structures; 

| > typically the design lives much longer than a single boxes' lifespan ;-)
| Indeed, and that's why you, as well as any other vendor, should be concerned
| with the effects that recommendations you make have on the larger routing
| system.   This isn't about Cisco, Juniper or insert_vendor_here, don't make
| it.  It's about clean network architecture, something that will effect not
| only the local routing system, but distant networks as well.

don't get me wrong;
i did not want to ride the "lets burn memeory, coz we have lots of them" wave
its simply that too often i have seen network architectures being built around the
limitations of a 20K$ box; the extra 10% of memory that diverse cluster IDs do 
cost IMHO outweight the administration cost of maintaining the intracluster
full-mesh; if a box does not stand that extra few MBs then it should not belong
in the core;


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