Yes, you are correct about the source of confusion :) I was gng through various sites in trying to prepare for the written exam. However, I am not sure if Implicit Null be advertised for any other prefix apart connected & summary. Thanks
________________________________ From: Nicola Arnoldi <[email protected]> To: Narendra Naukwal <[email protected]> Cc: "[email protected]" <[email protected]> Sent: Sunday, 7 April 2013 9:41 PM Subject: Re: [OSL | CCIE_RS] MPLS - PHP http://cciebible.com/ccie-rs-350-001-qas-implement-mpls-layer-3-vpns-1-5/ On Sun, Apr 7, 2013 at 5:00 PM, Nicola Arnoldi <[email protected]> wrote: Yes, re-reading your problem clearly shows that I was wrong, and your assumption is totally correct. >You advertise an implicit-null whenever you have to perform an IP lookup at >the E-LSR. > > >After a bit of Googling, I can guess your question comes from the various exam >dumps you can find on the Internet, which claim that the statement "PHP is >used only for directly connected subnets or aggregate routes" is wrong. > > >That's a good spot, however. > > > > > >On Sun, Apr 7, 2013 at 4:49 PM, Nicola Arnoldi <[email protected]> >wrote: > >try reading this >>http://blog.ioshints.info/2011/07/penultimate-hop-popping-php-demystified.html >> >> >> >> >>On Sun, Apr 7, 2013 at 4:15 PM, Narendra Naukwal <[email protected]> >>wrote: >> >>Hi, >>> >>>Thanks for looking into, however, I am not sure if i understand it completly. >>>My question is For what routes will a PE advertise an IMPLICIT NULL label? >>>I know it does advertises Implicit null (LDP value 3 or TDP Value 1) for >>>prefixes that need an IP lookup on the PE itslef. >>>The only route types that come to my mind are route 'Connected'on PE & >>>Routes 'Aggregated'for PE. >>> >>>By the way a router will generate a MPLS label for every prefix installed in >>>RIB via IGP. This I beleive has nothing to do with implicit null. >>> >>>For Example: >>>R3----mpls----R1---R2 (2.2.2.2) >>>| | >>>(3.3.3.3) (1.1.1.1) >>> >>>MPLS is not enabled on the link between R1 & R2 & OSPF is the configured >>>IGP. R1 learns about 2.2.2.2 via OSPF >>> >>>R1#sh ip route ospf >>> 2.0.0.0/32 is subnetted, 1 subnets >>>O 2.2.2.2 [110/11] via 12.0.0.2, 00:20:44, FastEthernet0/0 >>> 3.0.0.0/32 is subnetted, 1 subnets >>>O 3.3.3.3 [110/11] via 13.0.0.3, 00:20:13, FastEthernet0/1 >>> >>>Although MPLS is not enabled between R1 & R2, however, R1 still genarates & >>>advertises a label to R3 (100 in this case). >>> >>>R1#sh mpls forwarding-table >>>Local Outgoing Prefix Bytes tag Outgoing Next Hop >>>tag tag or VC or Tunnel Id switched interface >>>100 Untagged 2.2.2.2/32 0 Fa0/0 12.0.0.2 >>>101 Pop tag 3.3.3.3/32 0 Fa0/1 13.0.0.3 >>> >>>R1 advertises this to R3 & R3 uses 100 as otugoing label: >>>R3#sh mpls forwarding-table >>>Local Outgoing Prefix Bytes tag Outgoing Next Hop >>>tag tag or VC or Tunnel Id switched interface >>>300 100 2.2.2.2/32 0 Fa0/0 13.0.0.1 >>>301 Pop tag 1.1.1.1/32 0 Fa0/0 13.0.0.1 >>> >>>So the question remains, is there a scenario in IPv4 or VPNv4 when an EDGE >>>router will advertise an Implicit label aprt for connected & aggregated >>>routes? >>> >>>Thank You. >>>From: Nicola Arnoldi <[email protected]> >>>To: Narendra Naukwal <[email protected]> >>>Cc: "[email protected]" <[email protected]> >>>Sent: Sunday, 7 April 2013 7:10 PM >>>Subject: Re: [OSL | CCIE_RS] MPLS - PHP >>> >>> >>> >>>It is used as well for every route the Edge LSR learns from a PE to CE >>>routing protocol. No MPLS=PHP. >>> >>> >>> >>>On Sun, Apr 7, 2013 at 8:16 AM, Narendra Naukwal <[email protected]> >>>wrote: >>> >>>Experts, >>>> >>>>Is there a scenario wherein an Edge LSR signals an Implicit Null label to >>>>its directly connected Upstream neighbor for a subnet other which is not >>>>Connected or Summarized on the Edge LSR? >>>> >>>>Thank You. >>>>Naren >>>>_______________________________________________ >>>> For more information regarding industry leading CCIE Lab training, please visit http://www.ipexpert.com/ >>>> >>>>Are you a CCNP or CCIE and looking for a job? Check out >>>>http://www.platinumplacement.com/ >>>> >>>>http://onlinestudylist.com/mailman/listinfo/ccie_rs >>>> >>> >>> >>> >> > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com Are you a CCNP or CCIE and looking for a job? Check out www.PlatinumPlacement.com http://onlinestudylist.com/mailman/listinfo/ccie_rs
