Re: mpls peering questoin

This is best practice and not an absolute requirement. It's to make sure we donbt use a less specific router from ingress
to egress PE

If you have a /24 configured on the the loopback interface, by default
OSPF advertises the prefix for the loopback as a /32 (host route) regardless
of the subnet mask configured, LDP on the other hand will advertise it
according to the configured subnet mask.

In OSPF If you configure ip ospf network point-to-point ospf will advertise the prefix
according to the configured network mask. If you do this then the FEC advertised
by LDP and the ospf advertised prefix will match. Data plane and control plan with work and traffic will flow.

I would always recommend you configure your PE loopback interfaces using a /32

The reason traffic does not flow when there is a mis-match is because the label switched path is not setup properly because the LDP FEC (/24) and the ospf prefix (/32) donbt match.

--
BR
Tony
> On 30 Aug 2014, at 19:46, Imran Ali <immrccie_at_gmail.com> wrote:
> 
> Hi experts
> 
> Why it  is  necessary  to have  two PE routers  peer  with  a  loopback
> of   subnet mask 32
> 
> ios  gives  a  warning  in case  if  the  addresses  do not have  /32
> subnet mask .
> 
> 
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