MPLS Part 2 Intro || LDP || VRF

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Discovering LDP Neighbors

o Like IGPs , LDP automatically discovers neighbours with Hello Protocol
o Hellos use multicast UDP
   o 224.0.0.2 - " All routers Multicast "
   o UDP SRC & DST Port 646

o Hello include "IPv4 Transport Address"
    o Address to use for the TCP session
    o Defaults to the LDP router-id

o Forming LDP Adjacencies
    o LDP sessions are formed reliably over TCP
         o unicast between transport address
         o TCP port 646


o Implies peers must have routes to each other's transport address
      o e.g their loopbacks

o Transport address could be modified but not normally needed
     o Like IGP , hardcoding router-id is recommended

Advertising Labels:
o Once LDP session is established , label is advertised
   for FEC
     o i.e label to IPv4 prefix mapping

o Label distribution can be implicit or explicit
   o unsolicited downstream vs downstream on demand
   o depends on implementation & config option

o Labels could be advertised for some or all routers
o Cisco default is all IGP routes
o Really only /32 loopback matters

LDP Configuration

Enable CEF
   o Should already be on by default
 
Agree on label protocol
    o MPLS label protocol
    o Should already be LDP by default

Recommended to define router - id
    o MPLS LDP router id

Enable LDP
    o interface mpls ip
    o IGP process : mpls ldp autoconfig

LDP Verification
   o Verify LDP is enabled
   o show mpls interfaces

Verify LDP sessions
   o  show mpls ldp neighbor

Verify LFIB
   o show mpls forwarding-table

Note : need to allow LDP via ACL

ip access-list extended ACL
permit udp any eq 646 host 224.0.0.2 eq 646
permit tcp any any eq 646
permit tcp any any eq 646 any

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VRF : Virtual routers insie IOS

o VRF defines a new instance of the routing table
o Interface assigned to the VRF belong to that routing table.
o Interfaces not in a VRF are in the "global" or "default" vrf

Result in essentially a VPN

o Separate control plan instances
o Separate data plan based on routing
o e.g i cannot reach you if i have no route to you
o addressing can overlap in different VRF

VRF Aware Routing
o Routing inside a VRF can be through .....
o VRF aware static routes
o VRF aware dynamic routes
        o RIP
        o EIGRP
        o OSPF
        o IS-IS
        o MP BGP
o Policy Routing

Creating VRFs
o Specify locally significant VRF name
     . ip vrf [name]
     . IPv4 only
     . vrf Defination [name]
- supports both IPv4 & IPv6

Specify "route distinguisher"
    rd [ASN:nn | ip-address:nn ]
   more on this MP BGP

Applying VRFs
   o Apply VRF to interface
     o ip vrf forwarding [name] | vrf forwarding [name]
    o removes ip address from interfaces

This minimum configuration is called "vrf lite"
     o i.e VRFs without any mpls config
     o VRFs do not always means MPLS
     o MPLS does not always means VRFs

VRF Verification
      o show ip route vrf [vrf]
      o ping vrf [vrf]
      o traceroute vrf [vrf]


upgrade like this :
vrf upgrade-cli multi-af-mode common-policies

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