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
