MPLS labels

[Malik222]

Hello!

I'm preparing a small MPLS L3VPN lab to study for SPCORE. I got stuck at LDP - label filtering and advertising... Having difficulties understanding where the label filtering is supposed to be enabled in my lab... And what labels do I need to advertise? I deployed OSPF between the loopbacks of all of my routers and enabled LDP. But now I'm confused:
1. ) If I want to deploy an L3VPN service is it enough if I advertise only the PE loopback prefixes/label bindings? Or do all the loopbacks have to be advertised + all the other links?
2.) If I want to filter labels where is the most appropriate place? on the P? or on all devices?

BR,
Malik

[Giuseppe Larosa]

Hello @TangoAlfa ,

>> NOTE: its not L3VPN and loop back ip is /24 prefix.

if the loopback is not a /32 and your IGP is OSPF you need :

int loop x
ip ospf network point-to-point

the default behaviour of OSPF is to advertise loopbacks as /32 regardless of their effective subnet mask.

This causes a subnet mask , prefix lenght mismatch between OSPF route that is /32 and the LDP binding prefix that is /24.

using the command in loopback config makes OSPF to advertise the true subnet mask and it fixes the issues with LDP

Hope to help

Giuseppe

[TangoAlfa]

@Giuseppe Larosa Thanks its solved

[MHM Cisco World]

PE2 will exchange LDP with P1, 
Now PE2 want to know only about PE1"loopback", but P1 will send label for PE1<->P1 and label of PE1 loopback. 
But PE2 want only PE2 loopback for L3VPN, here we will use INBOUND FILTERING. 
INBOUND FILTERING to make PE2 only use the label of PE1 loopback.

IF you want to do LAB, 
before the INBOUND FILTERING do show mpls ldp binding, there is label for all Prefix 
after the INBOUND FILTERING do show mpls ldp binding, there is no label for filter prefix

NOTE INBOUND FILTERING:-
Neighbor is P1 ip address .

[Harold Ritter]

Hi Mahmood,

You could advertise only the Loopback interface addresses (/32) in your IGP if you wanted and this would still work. The advantage  of only advertising the /32 prefixes is that you can scale the IGP to a level that you would never reach if you advertise all core links in the IGP. 

Regards,

[TangoAlfa]

@Harold Ritter Hi the problem solved after making loopback as /32. now its showing PoP Label for other.