Suppose multiple sites end up using the same Site-id (VE-id) but participate in different VPLSs(differnent RTs) then RD will help distinguishing the layer-2 bgp-nlri for the layer2-routes for these sites. Isn't it?
Else (if RD is same or non-existent), advertisement for one site will mask the other's - assuming site-id, block-offset etc are same. Kaliraj On 6/27/07, Monika M <[EMAIL PROTECTED]> wrote: > Thanks for the reply. > As per section 3.1.2, Route target only identifies the VPLS. > Even in Juniper, if I have a configuration like this, > > root# show routing-instances > vplsinst2 { > instance-type vpls; > route-distinguisher 100:4; > vrf-target { > import target:100:3; > export target:100:3; > } > protocols { > vpls { > site-range 15; > site india { > site-identifier 7; > } > } > } > } > vplsinstance { > instance-type vpls; > interface fe-0/3/1.0; > route-distinguisher 100:3; > vrf-target { > import target:100:3; > export target:100:3; > protocols { > vpls { > site-range 10; > site vplsSiteA { > site-identifier 6; > interface fe-0/3/1.0; > } > } > } > } > > If a NLRI is received with RD as 100:3 and RT as 100:3, it is added to both > the VPLS instances. > Route tables vplsinst2.l2vpn.0 and vplsinstance.l2vpn.0 contain an entry for > the single NLRI. > > If the RT configuration is different and RD is same, then the NLRI is > associated only with the VPLS instance which is having the received RT. > Hence VPLS association is basically done with the RT and not with RD. That > is why it looks to me that RD is a redundant field. > > > Another feedback for the multi-homing input. > Having different RDs will lead to duplicate packets and loops (if you don't > run STP) as you treat them as two different prefixes and PWs are established > to both the peers leading to problem. I believe it is similar to having > different VE ID configuration stated in the RFC. > > > -Monika > > On 6/27/07, Guy Davies <[EMAIL PROTECTED]> wrote: > > > > Hi Monika > > > > On 27/06/07, Guy Davies <[EMAIL PROTECTED]> wrote: > > > Hi Monika, > > > > > > I haven't played around much with VPLS but a quick read of RFC 4761 > > > reveals the following... > > > > > > Section 3.5 of RFC 4761 appears to be the key. It refers to > > > multihoming mechanisms for VPLS and states the following... > > > > > > In the case where the PEs connected to the same site are assigned the > > > same VE ID, a loop-free topology is constructed by routing > > > mechanisms, in particular, by BGP path selection. When a BGP speaker > > > receives two equivalent NLRIs (see below for the definition), it > > > applies standard path selection criteria such as Local Preference and > > > AS Path Length to determine which NLRI to choose; it MUST pick only > > > one. If the chosen NLRI is subsequently withdrawn, the BGP speaker > > > applies path selection to the remaining equivalent VPLS NLRIs to pick > > > another; if none remain, the forwarding information associated with > > > that NLRI is removed. > > > > > > Two VPLS NLRIs are considered equivalent from a path selection point > > > of view if the Route Distinguisher, the VE ID, and the VE Block > > > Offset are the same. If two PEs are assigned the same VE ID in a > > > given VPLS, they MUST use the same Route Distinguisher, and they > > > SHOULD announce the same VE Block Size for a given VE Offset. > > > > > > In section 3.3, it states (paraphrasing) that you MAY configure an RD > > > on a PE for each VPLS. If you choose not to configure one manually > > > then one will be automatically created for each VPLS. > > > > > > So, (taking 3.3 and 3.5 together) if you want to do multihoming, you > > > MUST manually configure the same RD for the same VPLS on all the PE to > > > which multihomed sites in that VPLS are connected (so it makes sense > > > to configure the same RD on all PE for that VPLS). > > > > Sorry, I should say the following... > > > > So, (taking 3.3 and 3.5 together) if you want to do multihoming *and > > not use STP*, you MUST manually configure the same RD for the same > > VPLS on all the PE to which multihomed sites in that VPLS are > > connected (so it makes sense to configure the same RE on all PE for > > that VPLS). > > > > It has been pointed out to me that using the same RD will have an > > impact on the speed of convergence. Because the two prefixes are > > viewed as identical, the receiving PE will discard/ignore the other > > 'identical' advertisements. It must see a withdrawal of the first > > prefix and then an advertisement of the originally discarded/ignored > > prefix before the new prefix will be used. If the RDs (and hence the > > prefixes) are different, then only the withdrawal of the preferred > > prefix is required to trigger the use of the other prefix. > > > > > > Rgds, > > > > Guy > > > _______________________________________________ > juniper-nsp mailing list juniper-nsp@puck.nether.net > https://puck.nether.net/mailman/listinfo/juniper-nsp > _______________________________________________ juniper-nsp mailing list juniper-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/juniper-nsp