>MPLS:-The evolution of MPLS was Cisco’s TAG Switching however as it seems
it was Cisco’s proprietary so it must be used in Cisco world only,to make it
open standard IEEE made a similar kind of Protocol not as similar as Cisco’s
Tag switching however the idea was the same and they named it MPLS.MPLS is a
forwarding mechanism in which packets are forwarded based on labels,it means
no more routing lookups only labels are looked and forwarded in the ISP cloud,
so the movement becomes faster and the security enhanced.
As it was the new idea so the new terms are also attached with the logic behind
>LER :-Label Edge Router,is the router who is imposing or disposing the labels on
the each individual routes coming in or going out of the ISP cloud.LER is
commonly known as PE or Provider Edge Router.
>Ingress LER :-It is the PE router who is imposing the label in front of the IP
>Egress LER :-It is the PE router who is disposing the label and forwarding the IP
packet without label.
>LSR :-Label Switch Router,is a router that is doing forwarding of the packets
based on labels,also swapping the labels and tagging them with a new label,
commonly known as P or Provider router.
>CE :-Customer Edge router , is client site router connected to the ISP’s
>Label :-It is 4-byte(32 bit,same bit as in IP packet) identifier used in MPLS to
make forwarding decisions.
>Label Binding :-Mapping a label to a FEC.
>FEC :-It is a group of packets forwarded in the same manner,over the same path,
or with same forwarding treatment.
>LSP :-Label Switch Path , is series of LSR’s that forward labeled packets based
on the FEC.
>PHP :- Penultimate-Hop-Popping,it is a mechanism where the popping(removing) of
label is done one hop before the Egress PE router.
>RIB :- (Routing Information Base)It is like the Datacentre of all the routes
available in the router,that is further transferred into FIB for further forwarding.
>LIB :- (Label Information Base)It is like the Datacentre of all the labels bound to
networks available in the router,the labels are further move from LIB to LFIB for
You can check the LIB with the “Show mpls ldp bindings”
>FIB :- (Forwarding Information Base)Is a CEF(Cisco Express Forwarding) build table
from the information in the RIB,used for forwarding.
You can check the FIB with the “Show ip route”
>LFIB :- (Label Forwarding Information Base)Is a CEF table used for forward labeled
packets,the LFIB only stores the labels used to forward packets.
You can check LFIB with the “sh ip mpls forwarding-table”
>Control Plane :-Uses the configured routing protocols to build a routing table,
called the RIB,uses a label exchange protocol to maintain labels internally in a
table called the LIB.Is also responsible for building two tables in the Forwarding
Plane,the FIB and the LFIB tables.
>Data/Forwarding Plane :-It consists of two tables,the FIB and LFIB which is
responsible for forwarding incoming packets either based on IP(unlabeled)or
using the label.It is also responsible to push/pop/swap of labels.
>LDP:- Label Distribution Protocol used for transporting labels into MPLS cloud,IEEE standard.
>TDP:- Tag Distribution Protocol it is also used for transporting labels into MPLS
cloud however it is Cisco’s proprietary.
Will be discussing the above topics scenario-wise in coming posts, so do watchout 🙂