Re: [bess] comment on draft-ietf-bess-ir

[Lucy yong <[e-mail]>]

Jeff,

RR does not change BGP next hop on the update. N1 and N2 can determine P-tunnel neighbor based on BGP next hop.

Lucy

-----Original Message-----
From: Jeffrey (Zhaohui) Zhang [mailto:[e-mail]] 
Sent: Wednesday, September 23, 2015 9:36 AM
To: Lucy yong; Eric Rosen; [e-mail]
Cc: [e-mail]
Subject: RE: [bess] comment on draft-ietf-bess-ir

Lucy, 

Perhaps you can elaborate the following then?

There is no BGP session between N1/N2 and N3. RR does not understand "upstream/downstream" neighbor.
Even on N1/N2/N3, upstream/downstream are wrt different flows. How do you configure such policies?

> > [Lucy] If each BGP session keeps track of P-tunnel neighbor state: 
> > 1) the downstream neighbor, 2) the upstream neighbor, or 3) N/A. A 
> > simple policy can suppress a lot distribution: redistribute a Leaf 
> > A-D route if and only if it is sent by a downstream neighbor. This 
> > ensures that ingress PE receives all the Leaf A-D routes from all the egress PEs.

Jeffrey

> -----Original Message-----
> From: Lucy yong [mailto:[e-mail]]
> Sent: Wednesday, September 23, 2015 10:31 AM
> To: Jeffrey (Zhaohui) Zhang <[e-mail]>; Eric Rosen 
> <[e-mail]>; [e-mail]
> Cc: [e-mail]
> Subject: RE: [bess] comment on draft-ietf-bess-ir
> 
> Hi Jeff,
> 
> As I said before, RR always need to distribute Leaf A-D routes.
> 
> Lucy
> 
> -----Original Message-----
> From: Jeffrey (Zhaohui) Zhang [mailto:[e-mail]]
> Sent: Wednesday, September 23, 2015 9:28 AM
> To: Lucy yong; Eric Rosen; [e-mail]
> Cc: [e-mail]
> Subject: RE: [bess] comment on draft-ietf-bess-ir
> 
> Lucy,
> 
> The point is that we rely on BGP distribution mechanism, and we cannot 
> expect RRs to do more than basic route distribution.
> 
> Jeffrey
> 
> > -----Original Message-----
> > From: Lucy yong [mailto:[e-mail]]
> > Sent: Wednesday, September 23, 2015 10:26 AM
> > To: Jeffrey (Zhaohui) Zhang <[e-mail]>; Eric Rosen 
> > <[e-mail]>; [e-mail]
> > Cc: [e-mail]
> > Subject: RE: [bess] comment on draft-ietf-bess-ir
> >
> > Hi Jeff,
> >
> > We seem across each other. Two potential optimizations I proposed: 
> > 1) suppress unnecessary redistribution; 2) method for child to 
> > change its patent. I am not clear which one example illustrates. 
> > Both need to work with and without RR.
> >
> > -----Original Message-----
> > From: Jeffrey (Zhaohui) Zhang [mailto:[e-mail]]
> > Sent: Wednesday, September 23, 2015 9:17 AM
> > To: Lucy yong; Eric Rosen; [e-mail]
> > Cc: [e-mail]
> > Subject: RE: [bess] comment on draft-ietf-bess-ir
> >
> > Lucy,
> >
> > Let's use this example to illustrate the points we tried to get through:
> >
> >         N1        N2
> >           \      /
> >            \    /
> >              RR
> >               |
> >               |
> >              N3
> >
> >
> > N3 originates a Leaf AD route. Originally the parent is N1 so the 
> > Leaf AD route has RT(N1). Then the parent changes to N2 so N3 sends 
> > an update with new RT(N2). There is no withdraw from N3 at all.
> >
> > The route and its update is sent by N3 to only the RR.
> >
> > If Constraint Route Distribution (RFC 4684) is used, only N1 will 
> > get the initial route, and when N3 sends the update, RR will 
> > withdraw it from N1 and send the route to N2.
> >
> > If that is not used, then both N1 and N2 will get the original route 
> > and the update. Because the RT(N2) in the update does not match N1, 
> > N1 will treat the update as an implicit withdraw.
> >
> > So, in the first case, N1 will get the withdraw that is controlled 
> > by the RR, which only follows BGP route distribution process and 
> > does not understand MVPN/IR rules at all. In the second case, there 
> > is no explicit withdraw at all. In both cases, N3 only sends an update.
> >
> > Jeffrey
> >
> >
> > > -----Original Message-----
> > > From: Lucy yong [mailto:[e-mail]]
> > > Sent: Wednesday, September 23, 2015 9:58 AM
> > > To: Eric Rosen <[e-mail]>; Jeffrey (Zhaohui) Zhang 
> > > <[e-mail]>; [e-mail]
> > > Cc: [e-mail]
> > > Subject: RE: [bess] comment on draft-ietf-bess-ir
> > >
> > > Hi Eric,
> > >
> > > When non-segmented ingress replication is used, the ingress PE 
> > > needs to see the Leaf A-D routes from all the egress PEs.  (The 
> > > ingress PE is the upstream parent in this case, even if the 
> > > ingress PE is not a BGP peer of the egress PEs.)  This means that 
> > > the RT on the Leaf A-D routes needs to identify the ingress PE.  
> > > However, the Leaf A-D routes may need to travel over multiple BGP 
> > > sessions before they reach the
> > ingress PE.
> > > Some of these BGP sessions may be IBGP sessions, some may be EBGP
> > sessions.
> > > It's rather important that the route not get discarded before it 
> > > reaches the ingress PE, even though it passes through multiple BGP 
> > > speakers.  If one wants to constrain the distribution of the 
> > > routes, one still has to guarantee that the routes will reach their targets.
> > >
> > >
> > > [Lucy] If each BGP session keeps track of P-tunnel neighbor state:
> > > 1) the downstream neighbor, 2) the upstream neighbor, or 3) N/A. A 
> > > simple policy can suppress a lot distribution: redistribute a Leaf 
> > > A-D route if and only if it is sent by a downstream neighbor. This 
> > > ensures that ingress PE receives all the Leaf A-D routes from all 
> > > the
> egress PEs.
> > >
> > > Thanks,
> > > Lucy
> > >
> > >