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Traffic Engineering


1. Using MPLS TE in Real Life
2. Compare the RIB and FIB
3. LDP's 4 major function
4. Basic MPLS TE Tunnel Interface
5. Path-option command syntax
6. RSVP path setup

=============1. Using MPLS TE in Real Life ==============
Network engineering is manipulating your network to suit your traffic.v
Traffic engineering is manipulating your traffic to fit your network.
Traffic engineering, at its core, is the art of moving traffic around so that traffic from a congested link is moved onto the unused capacity on another link.

Using MPLS TE in Real Life

1, Optimizing your network utilization

2, Handling unexpected congestion

3, Handling link and node failures

=============>> 2. Compare the RIB and FIB <<================
7200a#show ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR



Gateway of last resort is 7.1.5.1 to network 0.0.0.0

B 171.68.0.0/16 [200/0] via 12.12.12.12, 01:10:44

3.0.0.0/32 is subnetted, 1 subnets

FIB
7200a#show ip cef 171.68.0.0

171.68.0.0/16, version 69, cached adjacency to POS3/0

0 packets, 0 bytes, wccp tag 139

via 12.12.12.12, 0 dependencies, recursive

next hop 10.0.3.5, POS3/0 via 12.12.12.12/32

valid cached adjacency


============> 3. LDP's 4 major function <==============

LDP's Major Functions
LDP has four major functions:

Neighbor discovery

Session establishment and maintenance

Label advertisement

Notification


Neighbor Discovery
Like most other network protocols, LDP has the concept of neighbors. LDP uses UDP/TCP ports 646 for discovery. LDP has two different types of neighbors:

Directly connected neighbors— These neighbors have a Layer 2 connection between them. So, routers that are connected by any Layer 2 link—whether a POS link, an ATM PVC, an Ethernet connection, or a DS-3 interface—are considered directly connected for LDP. Neighbors connected by a logical connection such as GRE tunnel are also considered directly connected. The basic commonality over such connections is the fact that a neighbor is one IP hop away.

Non-directly connected neighbors— These neighbors do not have a Layer 2 connection between them. More importantly, these neighbors are several IP hops away. Routers that are connected to each other by MPLS traffic engineering tunnels and that have LDP enabled on them are considered non-directly connected. Such an LDP session is called a targeted or directed LDP session.


The only difference between directly and non-directly connected neighbors is in how they discover each other. LSRs discover directly connected neighbors by sending LDP hello messages encapsulated in UDP to the 224.0.0.2 multicast address (all routers on a subnet). These packets are known as hello messages.

Non-directly connected neighbors can't be reached through a multicast UDP packet. So, the same hello messages are sent as unicasts (also to UDP port 646). This requires that an LSR know ahead of time who it wants to have as a non-directly connected neighbor. This can be achieved through configuration.


===========< 4. Basic MPLS TE Tunnel Interface >===========
Most commands that modify the behavior of a TE tunnel headend are configured on traffic engineering tunnels, as opposed to physical interfaces or in the global configuration. All the commands configured on a traffic engineering tunnel start with tunnel mpls traffic-eng. Keep this in mind as you learn more about how to configure tunnel interfaces.

interface Tunnel0

ip unnumbered Loopback0

tunnel mode mpls traffic-eng

tunnel destination destination-ip

tunnel mpls traffic-eng path-option 10 dynamic

Explaination:
interface Tunnel0: MPLS Traffic Engineering tunnels are represented as tunnel interfaces in the Cisco IOS Software. From this perspective, an MPLS Traffic Engineering tunnel is no different from a GRE tunnel or any other kind of tunnel you can configure.
ip unnumbered Loopback0: Cisco IOS Software does not forward traffic down an interface without an IP address on it, so you need to assign an IP address to the MPLS Traffic Engineering tunnel you've just created. However, because TE tunnels are unidirectional and don't have the concept of a link neighbor with which to communicate, it's a waste of addresses to put an additional IP address on the interface.
tunnel mode mpls traffic-eng: Tells the Cisco IOS Software that this tunnel interface is an MPLS Traffic Engineering tunnel. Other possible tunnel modes are GRE, DVMRP, and so on.
tunnel destination destination-ip: Tells the Cisco IOS Software what the tunnel's endpoint is. The IP address specified here is the MPLS Traffic Engineering RID (more on that later) of the router to which you want to build a tunnel. The destination-ip in this case is the Loopback0 interface on the tunnel's tailend router.
tunnel mpls traffic-eng path-option 10 dynamic Tells the Cisco IOS Software how to generate the path from the tunnel headend to the tunnel tail. This command is covered in more detail in Chapter 4.


=================== 5. path-optin command syntax ================

Table 4-16. tunnel mpls traffic-eng path-option Command Syntax Explanation Keyword Description
tunnel mpls traffic-eng path-option preference Defines a path-option for this tunnel. preference is a number from 1 to 1000. Different path-option values are tried in preference order from lowest to highest.

dynamic: Tells the router that it is supposed to calculate the best path that fits the configured tunnel constraints, such as band-width and affinity bits.

explicit: Allows you to specify an explicit path (configured separately) across the network that the tunnel will take. The explicit path also has to match the configured tunnel constraints, and the tunnel headend will check the explicit path to make sure that these constraints are met before trying to signal the path.

identifier identifier | name name: When explicit paths are created, they're given names or numbers. This option specifies which path option to consider.

lockdown: Configuring lockdown prevents a TE tunnel from being periodically reoptimized. See the later section "Tunnel Reoptimization."


=========== 6. RSVP path setup ================



1, R1 sends a Path message to R2. R2 receives the path message, checks to make sure that the message is syntactically correct, and checks with the TE Link Manager to make sure that the bandwidth R1 requested is actually available. If anything is wrong (the Path message is incorrectly formed or is asking for more bandwidth than R2 can provide), R2 sends an error message back to R1. Assuming that everything is good, move on to Step 2.

2, R2 sends a Path message to R3. R3 goes through the same verification of the Path message that R2 did.

3, R3 sends a Path message to R5; the same checks happen.

4, R5 sends a Path message to R6; the same checks happen.

5, R6 sends a Path message to R7; the same checks happen.

6, R7, being the tunnel tail, sends a Resv message to R6. This Resv message indicates the label R7 would like to see on the packet for this tunnel; because R7 is the tail, it sends implicit-null.

7, R6 sends a Resv message to R5 and indicates that it wants to see incoming label 42 for this tunnel. This means that when R6 receives label 42, it removes that label (because of implicit-null) and sends the packet toward R7.

8, R5 sends a Resv message to R3, signalling label 10921. When R5 receives a packet with label 10921, it swaps that label for label 42 and sends the packet to R6.

9, R3 sends a Resv message to R2, signalling label 21.

10, R2 sends a Resv message to R1, signalling label 18.

At this point, R1 is done. It has received a Resv message for the tunnel to R7 it set up, and it knows which outgoing label to use. The Tunnel interface on R1 now comes up/up (until this point, the Tunnel interface is up/down).