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
