TS INE V1:1.1

USEFULL COMMANDS:

sh cdp neighbor
sh int status
sh vlan br
ping
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PROBLEMS FACED:
1) In the output of sh cdp ne cmd some devices are missing based on L2 diag.
- Because, directly connected interfaces were shutdown.
- based on the L2-diag we know the directly connected devices.
- After using no shutdown on  connected interfaces  then only directly connected devices appear in sh cdp neigh cmd.
2) un successful of ping cmd
- some times interfaces were shutdown
- some times switches between source & destination have

• required vlans are not created
• in between source to destination every switch must contain corresponding vlan
• check the required vlans & corresponding interfaces by using sh vlan br
• then create vlans according l3-diag
• create vlan around switches from diagrom
• Some interfaces of switches are connected routers but not showed in L3-dag
• easily identified by a straight line connected to 2 or more devices
• some times simply a straight line
• That inter faces are connected to switches
• 
  

Label Switching Functions

• In label switching, analysis of the layer 3 header is done only once.
• After this analysis, add a fixed length, unstructured value called a label.
• Many different header add to the same label (those headers are have same next hop)
• i.e. a label represents a forwarding equivalence class
• Means a set of packets which are different but they are indistinguishably by the forwarding function.
• The initial choice of label may not depend upon the content of layer 3 packet header
• Ex: Forwarding decisions at subsequent hops can also be based on routing policies.
• The packet header need not be reanalysis  during packet transit through the network.
• Because the label is fixed length and unstructured.
• So the MPLS forwarding table lookup process is straight forward & fast

MPLS BENEFITS

• Highly Scalable
• In VPN(Virtual Private Networks) MPLS support any-to-any communication among VPN sites
• for this no requirement of full mesh of PVCs or sub optimal routing.
• Explicit Routing capabilities. 
• It will be possible due to the MPLS Traffic Engineering.
• MPLS enables an ATM switch to perform virtually all of the functions of an IP router.
• Eliminates the dependence on particular OSI layer technology.
• Eliminate the need for multiple layer-2 networks to satisfy different types of traffic

MPLS terminology

• LSR: Label Switch Routher
• A router forward IP Packets based on the Labels.
• Edge-LSR:
• A router at the end of MPLS network.
• which forward both labeled & unlabeled packets
• Ingress E-LSR:
• A router at an end of MPLS network(Edge-LSR or E-LSR), which add labels to the unlabeled & labeled ip packets.
• Egress E-LSR:
• A router removes the labels of received labeled ip packet & forward as unlabeled.
• CE Router: Customer Edge Router

MPLS

Introduction:

• Generally in ip routing, packets are forward based on the ip address
• But in MPLS, ip packets are assigned with labels.
• Gnerally when forwarding ip packet, whole packet will be read. then forward
• But in MPLS, read only the top label, based on this info ip packet will be forwarded 
• Today MPLS is, for the most part, it is a standardized version of Cisco's proprietary "tag switching".
• Before using the MPLS you must enable the CEF (Cisco Express Forwarding) on the router.