Hi Jorge, Ali, > [JORGE2] In VPWS DF election is needed for single-active. The NDF will > block the AC for the service.
> [JORGE] This is single active, so only one can transmit/receive to/from > the CE. So only that one should send P=1. If I understand it correctly, the draft should specify the following: - Use of DF election to determine primary/backup (curious how it is done for plain old EVPN), including backup DF concept - Only the current DF should set the P-bit - Only the current BDF should set the B-bit - P=B=1 is invalid - There could be transient situations where multiple P=1 and/or multiple B=1 routes co-exist. Some heuristic should be used to pick which one to use to avoid traffic discard at the other end. For the P=B=0 case - the receiving router can't use it anyway until its P/B is changed, right? If you want to use it as 2nd backup, the spec needs to point it out. Thanks. Jeffrey > -----Original Message----- > From: Rabadan, Jorge (Nokia - US) [mailto:[email protected]] > Sent: Thursday, May 12, 2016 2:28 PM > To: Jeffrey (Zhaohui) Zhang <[email protected]>; BESS <[email protected]> > Subject: Re: [bess] FW: WG Last Call (including implem status & shepherd) > for draft-ietf-bess-evpn-vpws-03 > > HI Jeffrey, > > > On 5/12/16, 8:13 PM, "BESS on behalf of EXT Jeffrey (Zhaohui) Zhang" > <[email protected] on behalf of [email protected]> wrote: > > >Hi Jorge, > > > >> >If a PE sends a route w/o setting P-bit, wouldn't that indicate it is > a > >> backup? Why would it bother sending the route if it does not want to be > >> the backup? > >> > >> [JORGE] Let’s assume you have 3 PEs in ES-1 (PE1/2/3) that is a single- > >> active ES. PE4 is a remote PE doing backup function. > > > >I assume PE4 is not "doing backup function" but is just one end of the PW. > Or perhaps you mean it needs to decide which of PE1/2/3 is the > primary/backup. > > [JORGE2] by “doing backup function” I mean that PE4 sets up a destination > to PE1 with a backup to PE2. Aliasing and Backup functions are effectively > done by the remote PEs based on the information advertised by the PEs in > the ES, right? > > > > >> - PE1 is the primary - the winner of the DF election. PE1 sends P=1 > >> - PE2 is the backup - the winner of the DF election (without PE1). PE2 > >> sends B=1. > > > >Hmm ... DF election is for BUM in RFC 7432 and never mentioned in this > draft. If it is used for VPWS, it needs to be specified. > > [JORGE2] In VPWS DF election is needed for single-active. The NDF will > block the AC for the service. For all-active there is no DF, of course, > since there is no BUM ;-) > > > > >The draft says multiple PEs could all set the P/B bits: > > > > In multihoming single active scenario, a remote PE receiving P=1 from > > more than one PE will select only one primary PE when forwarding > > traffic. A remote PE receiving B=1 from more than one PE will select > > only one backup PE. A remote PE MUST receive P=1 from at least one PE > > before forwarding traffic. > > > >And the decision is based on the receiving PE, not on DF election? > > [JORGE] This is BGP, there are always transient situations, so it may > happen that even in single active you get more than one P=1 or B=1, so you > need to say what to do in that case, right? In a steady situation, in > single-active MH, only the DF MUST send the P=1 since it is only the DF > the one unblocking the AC in the ES. > > > > >> - PE3 then sends P=B=0. This indicates that PE3 is neither primary nor > >> backup, but the AC is active (if it was oper-down, it would withdraw > the > >> route). > > > >What purpose does the route from PE3 serve? > > [JORGE] since the AC is oper-up on PE3, PE3 needs to send the route. At > PE4 you know that PE3’s AC in the ES is good, but simply neither primary > nor backup. > > > > >> - In case of a failure on PE1, PE2 will activate its AC on ES-1 since > he > >> wins the new DF election. > > > >What does "activate" involve exactly? Just re-advertise the route with P- > bit set and B-bit cleared? > > [JORGE] unblock Tx/Rx on the AC… and later readvertise the route with the > new bits. > > > > >> At the same time, PE4 can immediately send > >> traffic to PE2 as soon as PE1 withdraws the AD routes. PE4 does not > even > >> need to wait for the confirmation that PE2 is the new DF. This backup > >> mechanism speeds up convergence big time. > >> - The mechanism above does not work if PE2 and PE3 send both the same > >> P=B=0, since it case of PE1 failure, PE4 could not send any traffic (it > >> does not know who is the active one in the ES) and would need to wait > for > >> PE2 to send P=1. > > > >I don't see any use of the route from PE3. The draft seems to say that > both PE1 and PE2 can set the P bit initially and PE4 will pick one to send > traffic to. If it picks PE1 and then PE1 withdraws the route, PE4 will > then pick PE2? > > [JORGE] This is single active, so only one can transmit/receive to/from > the CE. So only that one should send P=1. > > > > >Jeffrey > >_______________________________________________ > >BESS mailing list > >[email protected] > >https://www.ietf.org/mailman/listinfo/bess _______________________________________________ BESS mailing list [email protected] https://www.ietf.org/mailman/listinfo/bess
