P routers have no knowledge of the customer prefixes, they just Label switch the packets based on their LFIB

Unanswered Question
Mar 1st, 2010

Here is a scenrio,

(1.1.1.0)CE1-PE1-P-PE2-CE2(2.2.2.0)

P router has no customer routes in its routing table, since it is not participating in iBGP.. thats perfect....


but P routers are meant to label switch packets between CE-1 & CE-2 through PE1 & PE2.. but i cannot see any labels for customer routes in P LFIB:

/* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin-top:0in; mso-para-margin-right:0in; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0in; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin;}

P#sh mpls for

Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop

tag    tag or VC   or Tunnel Id      switched   interface

16     Pop tag     10.10.10.11/32    6703       Se0/1      point2point

17     Pop tag     10.10.10.10/32    2140       Se0/0      point2point

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Loading.
Chetan Kumar Ress Mon, 03/01/2010 - 01:59

Hi Mukarramjahraheel 

You are right . P will not participating in iBGP. He is not aware of any Customer router of BGP VPNv4 route..

P Router know only internal IGP. Please go through the below points.

The JOB of Core router is to propogate the route As Fast As Possible without delay.

Don't Get confuse in MPLS . MPLS is used for only  Fast switching . Whouth MPLS also you can RUN  VRF kown as VRF - Lite , BGP - AF & use CEF for fast switching.

Before Going Further Please check you Design = Whether You want to Create Full Mesh IBGP  or Go With  BGP Route Reflector.

Communication from CE to PE

PE routers translate into VPN-V4 route

Assigns an RD, SOO (if configured) and RT based on configuration

Re-writes Next-Hop attribute  (to PE loopback ) -- When PE Re-Write the Next HOP , That next hop will  IBGP VPNv4 Neighbore PE and that is reachable through internal IGP. MPLS work only for Internal IGP to forward the packet AFAP without delay .

Assigns a label based on VRF and/or interface

Sends MP-BGP update to all PE neighbors

Receiving PE routers translate to IPv4

Insert the route into the VRF identified by the RT

attribute (based on PE configuration)

The label associated to the VPN-V4 address will be set on

packets forwarded towards the destination

Attachment: 
Mukarram Jah Raheel Mon, 03/01/2010 - 02:07

Hi,

thanks for ur reply......

to summarize, P will only have Labels in LFIB for label switching of traffic between the PEs, P will only have routes to PEs and Ps.. ?/

Regards

MukarraM

Mukarram Jah Raheel Mon, 03/01/2010 - 02:10

"Don't Get confuse in MPLS . MPLS is used for only  Fast switching . Whouth MPLS also you can RUN  VRF kown as VRF - Lite , BGP - AF & use CEF for fast switching."

in case MPLS is not configured, P routers will have to participate in routing between CEs and multiple contexts of IGP will be required to seperate their VPNs and overlapping address space..

MukarraM

Mukarram Jah Raheel Mon, 03/01/2010 - 02:30

Hi,

thanks for ur reply......

to summarize, P will only have Labels in LFIB for label switching of traffic between the PEs, P will only have routes to PEs and Ps.. ?/

Regards

MukarraM

Chetan Kumar Ress Mon, 03/01/2010 - 08:03

If you perform Summarization at P router then it Break the LSP .

And then P router will not use the existing Label . He will assign new label.

For Example :  If PE router is assign the label 50 & the same announce to all LDP neighbore then all

Other neighbore will work on same network but when P router summarlize that route then it is asume as a new network , So it will assign New Label for that Network. And fro Reverse traffic router will perform IP lookup for same & the Forward towards orignal network.

But in Cell Mode it can create issue , So while Deploying  be carefully !!!

Regards

Chetan Kumar


Actions

This Discussion