Basic MPLS - Intro

Basic MPLS

MPLS - Multi-Protocol Label Switching.

Operates at OSI layer 2.5. This position provides additional features for the transport of data across networks.

Traditional IP Networks:

Each router on service provide network, does route lookup (IP routing) to decide next-hop where it needs to forward packets to. Each router performs an independent decision on where to forward packet to. This repeated check happens on every device where the packet has to transverses across.

MPLS Enabled Networks;

Instead of IP lookup, MPLS enabled network rely on label switching which is fast and needs less resources on routers where it transverses.

First router(INGRESS) does IP lookup and all routers within Service provider does Label switching until the packet arrives at the LSR router(which is directly connected to egress PE) where outer label is stripped off (PHP) and the packet together with inner label passed to LSP destination (Egress PE).

MPLS Label:

a). Inner label -- Identifies vrf at which IP lookup will be performed

b). Outer label -- Identifies egress where packet for the label need to be stripped at.

PHP - Penultimate Hop Popping - Egress PE sends a label with a tag of 3 (label known as implicit-null) instructing a LSR to perform PHP on its behalf. This saves a lot of processing on the Edge router.

USES of MPLS:

i). MPLS VPN.

ii). MPLS Traffic Engineering.

iii). Path Protection.

END.