Agree; but do not forget that you can alwys add direct connections between clients (if I am not forgotten something). If 2 clients have direct link between them, it may be a good practice to add direct iBGP connection.
It means that iBGP topology should reflect (more or less) network one. Else you can have non-optimal (but still consistant and correct) routing. ----- Original Message ----- From: "David Barak" <[EMAIL PROTECTED]> To: <nanog@merit.edu> Sent: Wednesday, January 12, 2005 4:20 AM Subject: Re: IBGP Question --- Router Reflector or iBGP Mesh > > > --- Alexei Roudnev <[EMAIL PROTECTED]> wrote: > > > > > Are you sure? RR should just distribute routes. > > > > RR do not make any route decisions, and (btw) iBGP > > do not make route > > decisions - they are mostly based on IGP routing. > > All iBGP + RR are doing > > is: > > - tie external routes to internal IP; > > - distribute this information using iBGP mesh, RR's > > etc. > > - receive this information and set up routing using > > internal IP (which are > > routed by IGP protocls). > > > > End routers receives iBGP routes and uses IGP (OSPF > > or EIGRP or anything you > > use) for route decisions (of course, we can image > > exceptions, but normally , > > it works so that all decisions are based on IGP > > routing). Most important > > decisions are done , where routes are emitted from > > EBGP into iBGP, others - > > by iGP; which decisions are done by RR's themself? > > The primary decision made by a route-reflector is the > same decision which would be made by multiple routers > in an iBGP full-mesh: which exit point should this > router use to reach a specific netblock. > > Leaving aside for the moment any manipulation of > multipath, each router will run the BGP route > selection algorithm on each route learned. If > multiple routes are learned to a given destination, > only one will be inserted into the RIB. The standard > behavior for a router is to only pass on those routes > which have been accepted into the RIB. > > So if you have this network > > C1 -R1--R2-C2 > | | > C1 -R3--R4-C3 > > And R1 is the only route-reflector (yeah, yeah, bad > design - it's just an example), R4 will only learn > about the path to C1 through R1, and might route > traffic along the R4->R2->R1->C1 path rather than > along the R4->R3->C1 path which would be preferred by > an iBGP full-mesh. > > The upshot of this is the following (drumroll): > route reflectors are a wonderful thing, but make sure > that their topology reflects and respects your > underlying IP network topology. If you don't, you can > get unpleasant consequences. > > > > ===== > David Barak > Need Geek Rock? Try The Franchise: > http://www.listentothefranchise.com > > > > __________________________________ > Do you Yahoo!? > Yahoo! Mail - Helps protect you from nasty viruses. > http://promotions.yahoo.com/new_mail
