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Alcatel-Lucent Routing Protocols
Module 1 — Introduction
Module 2 — Static Routing and Default Routes
Module 3 — Routing Information Protocol
Module 4 – Link-State Protocols
Module 5 — Open Shortest Path First
Module 6 — Intermediate System–to–Intermediate System
Module 7 — Border Gateway Protocol
Alcatel-Lucent Routing Protocols
Module 1 — Introduction
IP Addressing — Basic Subnetting
 Subnetting allows a network to be subdivided into smaller
networks with routing between them.
 With basic subnetting, each segment uses the same subnet
mask.
 Potential for wasting IP addresses on links that do not require
high client density
 Easiest to implement
 Required for classful routing protocols
 VLSM allows the use of different subnet masks for different
parts of the network.
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IP Addressing — VLSM
 Different subnet masks per network
 Routing protocols must advertise the subnet mask with
updates
 More efficient use of IP addressing than basic subnetting
 Requires a good understanding of subnetting
 RFC 1878 defines VLSM
 Routing protocols that support VLSM are:
 RIPv2
 OSPF
 IS-IS
 BGP
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IP Addressing Review
 IP addresses are broken into classes: A, B, C, and D
Class A: 255.0.0.0 or /8
Network
Host
Host
Host
Class B: 255.255.0.0 or /16
Network
Network
Host
Host
Class C: 255.255.255.0 or /24
Network
Network
Network
Host
Class D: 255.255.255.255 or /32
Multicast
Multicast
Multicast
Multicast
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Section Objectives
 Introduction to IP routing
 Review of IP forwarding
 Control plane vs. data plane functions
 Common layer 3 routing protocols
— Distance vector
— Link state
 Classful and classless addressing
 Variable length subnet masking
 Classless interdomain routing
 Private IP addresses
 Network address translation (NAT/PAT)
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Movement of Data
1.1.1.2
(MAC address = A)
2.2.2.2
(MAC address = D)
1.1.1.1
(MAC address = B)
2.2.2.1
(MAC address = C)
3.3.3.2
3.3.3.1
Source
Dest.
S
D
1.1.1.2
2.2.2.2
A
B
F
C
Data
S
Source
Dest.
WAN
1.1.1.2
2.2.2.2
PPP
F
C
Data
S
Source
Dest.
S
D
1.1.1.2
2.2.2.2
C
D
F
C
Data
S
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Packet Forwarding
 When a router receives a packet, it:
 Compares the destination IP address of the packet to the FIB
 Looks for the longest (most specific) match
 If no match is found, the packet is dropped.
 If the packet is to be forwarded, the next hop and egress
interface must be known.
 If a match is found, the packet is sent to the next-hop
address via the interface specified in the FIB.
 The next-hop is the next router in the path toward the
destination.
 The egress interface is required for encapsulation.
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Common IP Routing Protocols
 Legacy routing protocols:
 RIP version 1
 RIP version 2
 Modern routing protocols:
 OSPF
 IS-IS
 BGP
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Distance Vector Protocols
 Distance = How far away
 Vector = What direction (interface)
 RIPv1, RIPv2, and BGP are distance vector protocols
Int 1/1/2
Int 1/1/2
IP – 1.1.1.1
IP – 2.2.2.1
Int 1/1/1
IP – 3.3.3.1
Routing Table:
1.1.1.0 – Direct 1/1/2
3.3.3.0 – Direct 1/1/1
2.2.2.0 – 1 hop via 1/1/1
Alcatel-Lucent Interior Routing Protocols and High Availability
Int 1/1/1
IP – 3.3.3.2
Routing Table:
2.2.2.0 – Direct 1/1/2
3.3.3.0 – Direct 1/1/1
1.1.1.0 – 1 hop via 1/1/1
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Link-State Protocols







Link = An interface
State = Active or inactive interface
OSPF and IS-IS are link-state protocols
More complex than distance vector
Faster convergence
Triggered updates
Three databases:
 Adjacency — Neighbor database
 Topology — Link-state database
 Routing — Forwarding database
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Link-State Protocols (continued)
 Adjacency database
 Link-state database
 Forwarding database
RTR - C
Network
1/1/2
2.2.2.0/24
RTR - A
RTR - B
1/1/1
Adjacency Database
RTR-B – on 1/1/1
RTR-C – on 1/1/2
LSDB
2.2.2.0/24
– via 1/1/1 cost 20
– via 1/1/2 cost 40
Alcatel-Lucent Interior Routing Protocols and High Availability
Routing Table:
2.2.2.0/24 – via 1/1/1
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Routing Table Management
 Each routing protocol populates its routes into its RIB.
 Each protocol independently selects its best routes
based on the lowest metric.
 The best routes from each protocol are sent to the
RTM.
OSPF
RIP
RIB
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RIB
RTM
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Preference




The RTM may have a best route from multiple protocols.
Selection is based on lowest preference value.
The RTM sends its best route to the FIB.
This route is the active route and is used for forwarding.
RIP
RIB
OSPF
OSPF
RIB
RTM
FIB
BGP
OSPF
BGP
RIB
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Default Preference Table
Route type
Direct attached
Static
OSPF internal
IS-IS Level 1 internal
IS-IS Level 2 internal
RIP
OSPF external
IS-IS Level 1 external
IS-IS Level 2 external
BGP
Alcatel-Lucent Interior Routing Protocols and High Availability
Preference
0
5
10
15
18
100
150
160
165
170
Configurable
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
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IP Addressing — Classful and Classless
Classful
10.1.1.0/24
10.0.0.0
10.1.1.0
10.1.2.0/24
12.1.0.0/16
Routing Table:
12.1.0.0 – direct 1/1/2
192.1.1.0 – direct 1/1/1
10.0.0.0 – 1 hop via 1/1/1
192.1.1.0/24
Classless
10.1.1.0/24
10.1.1.0/24
10.1.1.0/24
10.1.2.0/24
Alcatel-Lucent Interior Routing Protocols and High Availability
10.1.2.0/24
192.1.1.0/24
12.1.0.0/16
Routing Table:
12.1.0.0/16 – direct 1/1/2
192.1.1.0 /24 – direct 1/1/1
10.1.1.0/24 – 2 hops via 1/1/1
10.1.2.0/24 – 1 hop via 1/1/1
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IP Addressing — VLSM
 Different subnet masks per network
 Routing protocols must advertise the subnet mask with
updates.
 High-order bits are not reusable.
 Routing decisions are made based on the longest match.
 A more efficient use of IP addressing than basic subnetting
 Requires a good understanding of subnetting
 RFC 1878 defines VLSM.
 Routing protocols that support VLSM are:
 RIPv2
 OSPF
 IS-IS
 BGP
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IP Addressing — VLSM Example
172.16.0.0 –
172.16.1.0 –
….
172.16.254.0 –
255.255.255.0 –
10101100.00010000.00000000.00000000 – Reserved for WAN segments
10101100.00010000.00000001.hhhhhhhh – First Ethernet segment
172.16.0.4 –
172.16.0.252 –
255.255.255.252 –
10101100.00010000.00000000.000001 hh – First WAN segment
10101100.00010000.00000000.111111 hh – Last WAN segment
11111111.11111111.11111111.111111 00 – WAN mask
10101100.00010000.11111110.hhhhhhhh – Last Ethernet segment
11111111.11111111.11111111.00000000 – Ethernet mask
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Alcatel-Lucent Routing Protocols
Module 2 — Static Routing and Default Routes
What a Router Needs to Know
1.1.1.0/24
1.1.1.1
2.2.2.0/24
R1
3.3.3.0/30
3.3.3.1
Routing Table:
1.1.1.0/24 – Direct
3.3.3.0/30 – Direct
2.2.2.0/24 – static via 3.3.3.2
2.2.2.1
R2
3.3.3.2
Routing Table:
2.2.2.0/24 – Direct
3.3.3.0/30 – Direct
1.1.1.0/24 – static via 3.3.3.1
• Routers need to know where networks are located and how best to
access them.
• This can be accomplished statically with administrative commands.
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Static Routes — Basic Static Routes
static-route 0.0.0.0/0 next-hop 3.3.3.1
R1
Corporate
Headquarters
3.3.3.1
2.2.2.0/24
R2
3.3.3.2
static-route 2.2.2.0/24 next-hop 3.3.3.2
• Configuration of static routes between stub
networks and corporate locations
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Static Routes — Configuration Example
2.2.2.0/24
Corporate
Headquarters
R1
3.3.3.1
R2
3.3.3.2
config>router> static-route 2.2.2.0/24 next-hop 3.3.3.2
config>router> static-route 0.0.0.0/0 next-hop 3.3.3.1
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Default Routes — Basic Default Route
2.2.2.0/24
R1
R2
Corporate
Headquarters
3.3.3.1
3.3.3.2
R2# show router route-table
============================================================================
Route Table
============================================================================
Dest Address
Next Hop
Type Protocol
Age
Metric
Pref
---------------------------------------------------------------------------3.3.3.0/24 System
Local Local
01d02h
0
0
2.2.2.0/24
System
Local Local
08d03h
0
0.0.0.0/0 3.3.3.1
Remote Static
01d02h
1
5
----------------------------------------------------------------------------
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Static Routes — Floating Static Routes
Backup
2.2.2.0/24
1.1.1.2
1.1.1.1
R1
Corporate
R2
Primary path
Headquarters
3.3.3.1
3.3.3.2
config>router> static-route 2.2.2.0/24 next-hop 3.3.3.2
config>router> static-route 2.2.2.0/24 next-hop 1.1.1.2 preference 200
• Configuration of a floating static route between stub
networks and corporate locations
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Static Route Verification — Show Command
 The command below shows static routes configured in
the routing table.
Context:
show>router>
Syntax: static-route [[ip-prefix [/mask]] | [preference preference] | [next-hop ip-addr] | tag tag
Example:
R1# show router route-table protocol static
==============================================================================
Route Table (Router: Base)
==============================================================================
Dest Address Next Hop
Type
Proto
Age
Metric
Pref
------------------------------------------------------------------------------2.2.2.0/24
3.3.3.2
Remote Static
00h01m34s
1
5
2.2.2.0/24
1.1.1.2
Remote Static
00h01m15s
1
200
------------------------------------------------------------------------------No. of Routes: 1
==============================================================================
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Static Route Verification — Show Command (continued)
2.2.2.0/24
Corporate
Headquarters
R1
3.3.3.1
R2
3.3.3.2
R1# show router route-table 2.2.2.0/24
==============================================================================
Route Table (Router: Base)
===============================================================================
Dest Address
Next Hop
Type
Proto
Age
Metric
Pref
------------------------------------------------------------------------------2.2.2.0/24
3.3.3.2
Remote
Static 00h02m54s
1
5
------------------------------------------------------------------------------No. of Routes: 1
==============================================================================
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Static Routes — Ping Command
2.2.2.2
2.2.2.0/24
Corporate
3.3.3.1
3.3.3.2
Headquarters
R1# ping 2.2.2.2 detail
PING 2.2.2.2: 56 data bytes
64 bytes from 2.2.2.2 via fei0: icmp_seq=0 ttl=64 time=0.000 ms.
64 bytes from 2.2.2.2 via fei0: icmp_seq=1 ttl=64 time=0.000 ms.
64 bytes from 2.2.2.2 via fei0: icmp_seq=2 ttl=64 time=0.000 ms.
64 bytes from 2.2.2.2 via fei0: icmp_seq=3 ttl=64 time=0.000 ms.
64 bytes from 2.2.2.2 via fei0: icmp_seq=4 ttl=64 time=0.000 ms.
---- 2.2.2.2 PING Statistics ---5 packets transmitted, 5 packets received, 0.00% packet loss
round-trip min/avg/max/stddev = 0.000/0.000/0.000/0.000 ms
R1#
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Static Routes — Traceroute Command
2.2.2.2
2.2.2.0/24
Corporate
Headquarters
R1
R2
3.3.3.2
3.3.3.1
R1# traceroute 2.2.2.2
traceroute to 2.2.2.2, 30 hops max, 40 byte packets
1 3.3.3.2
<10 ms
<10 ms
<10 ms
2 2.2.2.2
<10 ms
<10 ms
<10 ms
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Learning Assessment
1. Do static routes have a higher or lower preference value
than dynamic routes?
2. What is the command syntax to create a static route in
the 7750 SR?
3. A router has a default route, a static route to
10.10.8.0/24, and a route to 10.8.0.0/14 learned from
RIP. Which route is used for a packet with destination
address 10.10.10.10?
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Alcatel-Lucent Routing Protocols
Module 3 — Routing Information Protocol
Section Objectives
 Distance vector overview
 Split horizon
 Route poisoning
 Poison reverse
 Hold-down timers
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Distance Vector Overview
 Routers send periodic updates to physically adjacent
neighbors
 Updates contain the distance (how far) and vectors
(direction) for networks
RTR-B
RTR-A
100 Mb/s
1 Gb/s
1 Gb/s
1 Gb/s
RTR-C
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RTR-D
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Distance Vector Overview (continued)
 The router processes and compares the information
contained in the routing update received with what is in its
routing table.
Process
and compare
with routing
table
Periodic update
Update from neighbor
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Sent to neighbor
routers
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Split Horizon
 An adjacent router does not advertise networks back to the
source of the network information.
10.0.0.0 – 2 hops
RTR-A
Routing Table:
10.0.0.0 – 2 hops
via 1/1/1
Alcatel-Lucent Interior Routing Protocols and High Availability
10.0.0.0 – 1 hop
RTR-B
X
10.0.0.0
RTR-C
Routing Table:
10.0.0.0 – 1 hop
via 1/1/1
Routing Table:
10.0.0.0 – 0 hops
via 1/1/1
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Route Poisoning
 When a network goes away, the sourcing router sets the
hop value to infinity and sends a triggered update to its
neighbors.
10.0.0.0 – 16 hops
10.0.0.0 – 16 hops
10.0.0.0
X
RTR-A
Routing Table:
10.0.0.0 – 16 hops
via 1/1/1
Routing Table:
10.0.0.0 – 2 hops
via 1/1/1
Alcatel-Lucent Interior Routing Protocols and High Availability
RTR-B
RTR-C
Routing Table:
10.0.0.0 – 16 hops
via 1/1/1
Routing Table:
10.0.0.0 – 1 hop
via 1/1/1
Routing Table:
10.0.0.0 – 16 hops
via 1/1/1
Routing Table:
10.0.0.0 – 0 hops
via 1/1/1
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Poison Reverse
 Poison reverse is the only time that split horizon is violated.
This helps to avoid loop creation when a network fails.
10.0.0.0 — 16 hops
10.0.0.0 — 16 hops
Poison reverse
Poison reverse
10.0.0.0 — 16 hops
10.0.0.0 — 16 hops
10.0.0.0
X
RTR-A
Routing Table:
10.0.0.0 — 16 hops
via 1/1/1
Routing Table:
10.0.0.0 — 2 hops
via 1/1/1
Alcatel-Lucent Interior Routing Protocols and High Availability
RTR-B
RTR-C
Routing Table:
10.0.0.0 — 16 hops
via 1/1/1
Routing Table:
10.0.0.0 — 1 hop
via 1/1/1
Routing Table:
10.0.0.0 — 16 hops
via 1/1/1
Routing Table:
10.0.0.0 — 0 hops
via 1/1/1
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Hold-Down Timers
 Hold-down timers provide time for other routers to
converge and reduce loops from being created when a
network fails.
10.0.0.0 — 16 hops
10.0.0.0 — 16 hops
10.0.0.0
X
RTR-A
RTR-B
RTR-C
Routing Table:
10.0.0.0
162 hop
10.0.0.0–—
hops–
Via
via 1/1/1
Routing Table:
10.0.0.0– —
hop–
10.0.0.0
161hop
via 1/1/1
Via
1/1/0
Hold-down timer
180 seconds
Hold-down timer
180 seconds
Alcatel-Lucent Interior Routing Protocols and High Availability
Routing Table:
10.0.0.0–—
hops–
10.0.0.0
160 hop
via 1/1/1
Via
1/1/1
Module 0 |
Hold-down timer
180 seconds
37
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Combined Loop Avoidance Techniques
 Combined, all attributes function as follows:
10.0.0.0 — 16 hops
10.0.0.0 — 16 hops
Poison reverse
Poison reverse
10.0.0.0 — 16 hops
10.0.0.0 — 16 hops
10.0.0.0
X
RTR-A
RTR-B
RTR-C
Routing Table:
10.0.0.0
162 hop
10.0.0.0–—
hops–
Via
1/1/0
via 1/1/1
Routing Table:
10.0.0.0– —
hop–
10.0.0.0
161hop
via 1/1/1
Via
1/1/1
Routing Table:
10.0.0.0–—160 hop
hops–
10.0.0.0
via 1/1/1
Via
1/1/0
Hold-down timer
180 seconds
Hold-down timer
180 seconds
Hold-down timer
180 seconds
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RIP Overview






Uses a hop-count metric
Sends updates of the routing table to neighbors
Maximum of 15 hops; 16 hops equals infinity
30-second advertisement interval by default
Authentication is available in RIPv2
VLSM is supported by RIPv2
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RIP Overview (continued)
100 Mb/s
RTR-A
RTR-B
1 Gb/s
1 Gb/s
RTR-C
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1 Gb/s
RTR-D
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RIPv1 vs. RIPv2
RIPv1
RIPv2
Defined in RFC 1058
Defined in RFCs 1721, 1722, and 2453
Classful routing protocol
Classless routing protocol
No subnet mask in updates
Sends subnet mask in updates
Does not support VLSM
Supports VLSM and CIDR
No manual route summarization
Manual route summarization
Does not support authentication
Supports authentication
Broadcast updates
Multicast or broadcast updates
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RIP – Major Component Configuration
 Router
 Interface (assumed to be already complete)
 Route policies
 RIP
 Group
 Neighbor
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Alcatel-Lucent Routing Protocols
Module 4 – Link-State Protocols
Distance Vector vs. Link State
Distance vector
•Views the network topology
from the neighbor’s
perspective
•Adds distance vectors
from router to router
•Frequent, periodic updates:
slow convergence
•Passes copies of the routing
table to neighbor routers
Alcatel-Lucent Interior Routing Protocols and High Availability
Link state
•Has a common view of the
entire network topology
•Calculates the shortest
path to other routers
•Event-triggered updates:
faster convergence
•Passes link-state routing
updates to other routers
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Link State Overview
Link state-driven updates, periodic hellos
Classless routing protocol
Sends subnet mask in update
Supports VLSM, CIDR, and manual route summarization
Supports authentication
Maintains multiple databases
Sends updates using multicast addressing
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Link State Overview (continued)







Link = An interface
State = Active or inactive interface, cost
IS-IS and OSPF are link-state protocols
More complex than distance vector
Faster convergence
Triggered updates
Three databases:
 Adjacency – neighbor database
 Topology – link-state database
 Routing – forwarding database
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Link State Overview (continued)
 Adjacency database
 Link-state database
 Forwarding database
RTR - C
Network
1/1/1
RTR - A
2.2.2.0/24
1/1/2
Adjacency database
RTR-B – on 1/1/2
RTR-C – on 1/1/1
Alcatel-Lucent Interior Routing Protocols and High Availability
RTR - B
LSDB
2.2.2.0/24
via 1/1/2 cost 20
via 1/1/1 cost 40
Routing table
2.2.2.0/24 via 1/1/2
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Link State Overview (continued)
2.2.2.0/30
.1
10.0.0.0/8
.2
.2
Step 1 – Updates received
from peers
.1
3.3.3.0/30
Routing table
10.0.0.0/8 via 2.2.2.1
…
Step 2 – Topology database
created
10.0.0.0/8
Via 2.2.2.1 Cost 10
Via 3.3.3.1 Cost 20
…
Alcatel-Lucent Interior Routing Protocols and High Availability
Step 3 – SPF algorithm
determines the best
path to destination networks
Step 4 – Routing
table created
10.0.0.0/8
Via 2.2.2.1 Cost 10 – BEST
Via 3.3.3.1 Cost 20
…
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Exchanging Link-State Information
R1
A
R2
B
R1 Link-state packet
R3
C
R2 Link-state packet
D
R3 Link-state packet
A
10
B
10
C
10
B
10
C
10
D
10
Routers exchange LSPs with each other. Each begins with directly connected
networks for which it has direct link-state information.
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Building a Topological Database
R1
A
R2
B
R1 Link-state packet
R3
C
R1 Link-state packet
D
R1 Link-state packet
A
10
A
10
A
10
B
10
B
10
B
10
R2 Link-state packet
R2 Link-state packet
R2 Link-state packet
B
10
B
10
B
10
C
10
C
10
C
10
R3 Link-state packet
R3 Link-state packet
R3 Link-state packet
C
10
C
10
C
10
D
10
D
10
D
10
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Calculating the SPF Tree and Populating the Routing Table
R1
A
R2
B
R3
C
D
R1 Link-state packet
A
10
B
10
SPF
1
R2 Link-state packet
B
10
C
10
R3 Link-state packet
C
10
D
10
Alcatel-Lucent Interior Routing Protocols and High Availability
2
SPF tree
3
R1
Routing
table
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51
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SPF Algorithm
R1 LSDB
R3
10
10.0.0.0/8 (net1)
100
R1
5
R1,
R1,
R2,
R2,
R3,
R3,
R3,
R2, 5
R3, 10
R1, 5
R3, 100
R1, 10
R2, 100
net1, 0
R2
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SPF Algorithm (continued)
Step
R3
10
10.0.0.0/8 (net1)
100
Candidate
Cost to root
1
—
—
R1, R1, 0
2
R1, R2, 5
R1, R3, 10
5
10
R1, R1, 0
3
R1, R3, 10
10
R1, R1, 0
R1, R2, 5
4
R1, R3, 10
R2, R3, 100
10
105
R1, R1, 0
R1, R2, 5
5
R3, net1, 0
10
6
—
—
R1,
R1,
R1,
R1,
R1,
R1,
R3,
R1
5
R2
Alcatel-Lucent Interior Routing Protocols and High Availability
SPF tree
Module 0 |
53
R1, 0
R2, 5
R3, 10
R1, 0
R2, 5
R3, 10
net1, 0
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Link State – Topology Change
 Link-state updates are driven by topology changes.
Run SPF
Update
routing
table
Topology
change
Link-state information
Alcatel-Lucent Interior Routing Protocols and High Availability
Run SPF
Update
routing
table
Run SPF
Update
routing
table
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54
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Sequence Numbers
 Sequence numbers must be included in the link-state
information.
 Without sequence numbers, the link-state information could be
flooded indefinitely.
 The sequence number remains the same, router-to-router,
during the flooding process.
 In a link-state environment, routers use the sequence
numbers for the following decisions when they receive linkstate updates:
 If the sequence number is lower than the one in the database,
the link-state information is discarded.
 If the sequence number is the same as the one in the database,
an ACK is sent. The link-state information is then discarded.
 If the sequence number is higher, the link-state information is
populated in the topological database, an ACK is sent, and the
link-state information is forwarded to its neighbors.
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Sequence Numbers (continued)
A
R1
B
R2
R3
C
D
R1 Link-state packet
R1 Link-state packet
R1 Link-state packet
Seq=2
Seq=1
Seq=1
A
R1
B
R2
R3
C
D
R1 Link-state packet
R1 Link-state packet
R1 Link-state packet
Seq=2
Seq=2
Seq=1
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Sequence Numbers (continued)
 R1 receives 2 copies of the link-state information for
network Z.
— R1 must decide what to do with the second copy of the linkstate information it receives.
R1
B
R2
Cost 10
R3
C
Cost 10
Cost 10
A
Cost 10
F
R6
Cost 20
Alcatel-Lucent Interior Routing Protocols and High Availability
D
E
Z
Cost 20
R5
R4
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Link-State Information Aging
 Link-state information includes an age field.
 The age of newly created link-state information is set to 0 for
OSPF and 1200 for IS-IS. It is incremented by every hop during
the flooding procedure for OSPF and is decremented for IS-IS.
The link-state age is also incremented for OSPF and
decremented for IS-IS as it is held in the topological database.
 Maximum age
 When the link-state information reaches its maximum age, it is
no longer used for routing. The link-state information is
flooded to the neighbors with the maximum age, and the linkstate information is removed from the topological database.
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IS-IS – Packet Processing
 A router deals with topology changes as follows:
LSU/LSA
Is entry in
Yes
LSDB?
Ignore
same?
No
No
Add to LSDB
Send ACK
Yes
Sequence No.
Yes
Is sequence
number higher
than one in
LSDB?
No
Flood LSA
Send LSU back
with newer
information
Run SPF
End
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Hierarchy in Link-State Networks
 Scalability issues exist for link-state networks:
 The size of the link-state database increases exponentially with
the size of the network.
 The complexity of the SPF calculation also increases
exponentially.
 A topology change requires complete recalculation of the
forwarding table on every router.
 Hierarchy allows a large routing domain to be split into
several smaller routing domains.
 IS-IS and OSPF both implement hierarchy but use different
techniques.
 Hierarchy results in suboptimal routing.
 Hierarchy is less common than in the past due to the
increased capacity of routers.
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IS-IS – Hierarchical View
Integrated IS-IS Network
L1
L2
Area 2
L1/L2
L1
L1/L2
Area 3
L1/L2
L1
Area 1
Alcatel-Lucent Interior Routing Protocols and High Availability
L1
L2
L1/L2
Backbone (Level 2) links
Level 1 links
Level 1
Level 2
Level 1/Level 2
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OSPF – Hierarchical View (continued)
OSPF Hierarchical Routing
Area 0.0.0.0
Area 0.0.0.1
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Area 0.0.0.2
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Alcatel-Lucent Routing Protocols
Module 5 — Open Shortest Path First
OSPF — RFC History
1987
OSPF
workgroup
formed
OSPF v1
RFC 1131
defined
OSPF v2
RFC 1247
defined
OSPF v2
Updated
RFC 1583
OSPF v2
Updated
RFC 2178
OSPF v2
Updated
RFC 2328
OSPF
work in
progress
OSPF for
IPv6
RFC 2740
1989
1991
1994
1997
1998
1999
Present
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OSPF — Protocol Overview
Link state-driven updates, periodic hellos
Classless routing protocol
Subnet mask sent in update
Support for VLSM, CIDR, and manual route summarization
Support for authentication
Maintenance of multiple databases
Multicast addressing – 224.0.0.5 and 224.0.0.6
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OSPF — Key Features
 Key OSPF features are:
 Backbone areas
 Stub areas
 NSSAs
 Virtual links
 Authentication
 Support for VLSM and CIDR
 Route redistribution
 Routing interface parameters
 OSPF-TE extensions
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OSPF — Protocol Comparison
Feature
RIPv2
IS-IS
OSPF
Updates
Periodic
Incremental
Incremental
Update type
Broadcast/Multicast
L2 Multicast
L3 Multicast
Transport
UDP
Layer 2
IP
Authentication
Simple and MD5
Metric
Hops
Cost
Cost
Metric type
Distance vector
Link-state
Link-state
VLSM / CIDR support
Yes
Yes
Yes
Topology size
Small/Medium
Large
Large
Convergence
Slow
Fast
Fast
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Simple and MD5 Simple and MD5
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OSPF — Link-State Protocol Comparison
Feature
IS-IS
OSPF
Updates
Incremental
Incremental
Multicast layer
Layer 2
Layer 3
Authentication
Simple and MD5
Simple and MD5
Metric
Default: all ports cost 10
Auto-calculation on interface
Metric type
Link-state
Link-state
LSA types
L1 and L2
Multiple types
Area hierarchy
Not required
Backbone area
Area boundaries
On segment
At interface
Convergence
Fast
Fast
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OSPF — Path Determination
 OSPF uses SPF for path determination.
 SPF uses cost values to determine the best path to a
destination.
RTR-C
10.0.0.0
Cost 125
Cost 125
Cost 0
Cost 10
RTR-A
RTR-B
Cost 125
RTR-A
10.0.0.0 – Cost 260 via RTR C
*10.0.0.0 – Cost 135 via RTR B
* = Best path
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Calculating Link Cost
 Cost = reference-bandwidth ÷ bandwidth
 The default reference-bandwidth is 100 000 000 kb/s or
100 Gb/s.
 The default auto-cost metrics for various link speeds are as
follows:
— 10-Mb/s link default cost of 10 000
— 100-Mb/s link default cost of 1000
— 1-Gb/s link default cost of 100
— 10-Gb/s link default cost of 10
 The cost is configurable.
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Configuration Basics
 Interfaces must be configured in an OSPF area.
 By default, interfaces in an area are advertised by OSPF.
 Routes received through OSPF are advertised by OSPF.
 No other routes are advertised by default.
 Verify that adjacencies are formed with neighbors.
 Verify that routes are in the routing table.
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OSPF — Multicast Addressing
 OSPF uses class D multicast addresses in the range
224.0.0.0 to 239.255.255.255.
 Specially reserved addresses for OSPF:
 224.0.0.5: All routers that speak OSPF on the segment
 224.0.0.6: All DR/BDRs on the segment
 IP multicast addresses use the lower 23 bits of the IP
address as the low-order bits of the MAC multicast address
01-005E-XX-XX-XX.
 224.0.0.5 = MAC 01-00-5E-00-00-05
 224.0.0.6 = MAC 01-00-5E-00-00-06
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OSPF — Generic Packet
 OSPF packets use protocol number 89 in the IP header.
 OSPF is its own transport layer.
Link header
IP header
OSPF packet
types
Link trailer
IP header protocol
ID 89 = OSPF
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OPSF — Packet Types





OSPF
OSPF
OSPF
OSPF
OSPF
hello
database descriptor
link-state request
link-state update
link-state ACK
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74
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OSPF — Link Topology Types
Multi-access
Point-to-point
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OSPF — Router ID
 Each router must have a router ID, the ID by which the
router is known to OSPF.
 The default RID is the last 32 bits of the chassis MAC address.
 Configuring a system interface overrides the default.
— Using a system interface is easier to document.
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OSPF — Point-to-Point Segments




On point-to-point links, there is no need for a DR or BDR.
All packets are sent via IP multicast address 224.0.0.5.
Usually a leased-line (i.e., HDLC, PPP) segment
Can be configured on point-to-point Ethernets
RTR - C
Network
2.2.2.0/24
RTR - A
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RTR - B
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OSPF — LAN Communication
 Election of the DR and BDR in multi-access networks:
A
B
1.1.1.5
1.1.1.4
RTR-A
RTR-B
Has the highest
Has the second highest
RID, so it will be
RID, so it will be the BDR
the DR
C
D
E
1.1.1.1
1.1.1.2
1.1.1.3
 Each router sends hellos.
 The router with the highest priority is the DR.
 If all priorities are the same, the DR is the router with the
highest RID.
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OSPF — Exchanging Updates in a LAN
 Election of the DR and BDR in multi-access networks:
RTR-A (DR)
RTR-B (BDR)
1.1.1.5
1.1.1.4
RTR-C sends update to
RTR-A sends update to
All DRs using IP address
All OSPF routers using
224.0.0.6
IP address 224.0.0.5
RTR-C
D
E
1.1.1.1
1.1.1.2
1.1.1.3
 Routers use the 224.0.0.6 IP address to send updates to the
DRs.
 The BDR monitors the DR to ensure that it sends updates.
 The DR uses 224.0.0.5 to send updates to all OSPF routers.
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Alcatel-Lucent Routing Protocols
Module 6 — Intermediate System–to–Intermediate System
IS-IS — Protocol Overview
 Development began prior to that of OSPF.
 The U.S. government required ISPs to use IS-IS for early
stages of the Internet.
 IS-IS supports IPv6.
 Many large enterprise networks and ISPs use IS-IS due to the
scalability and stability of the protocol.
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IS-IS — RFC History
1990
RFC 1142
Original
RFC
RFC 1195
TCP/IP
support
1990
1992
ISO 10589
released
1994
…..
2002
RFC 1629
NSAP and
Internet
Other IS-IS
RFCs
released
Present
RFC 33509
TLV
code points
IS-IS
work in
progress
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IS-IS — Protocol Overview (continued)
Link-state driven updates, periodic hellos
Classless routing protocol
Subnet mask sent in update
Support for VLSM, CIDR, and manual route summarization
Support for authentication
Maintenance of multiple databases
Layer 2 multicast addressing
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IS-IS — Key Features
 Key IS-IS features are:
 Area hierarchy
 Authentication
 Support for VLSM and CIDR
 Route redistribution
 Routing interface parameters
 IS-IS TE extensions
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IS-IS — Protocol Comparison
Feature
RIPv2
OSPF
IS-IS
Updates
Periodic
Incremental
Incremental
Update type
Broadcast/Multicast
L3 Multicast
L2 Multicast
Authentication
Simple and MD5
Metric
Hops
Cost
Cost
Metric type
Distance vector
Link-state
Link-state
VLSM / CIDR support
Yes
Yes
Yes
Topology size
Small
Very large
Very large
Summarization
Manual
Manual
Manual
Convergence
Slow
Fast
Fast
Alcatel-Lucent Interior Routing Protocols and High Availability
Simple and MD5 Simple and MD5
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85
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IS-IS — Link-State Protocol Comparison
Feature
IS-IS
OSPF
Updates
Incremental
Incremental
Multicast layer
Layer 2
Layer 3
Authentication
Simple and MD5
Simple and MD5
Metric
Default: all ports cost 10
Auto-calculation on interface
Metric type
Link-state
Link-state
Update types
L1 and L2
Multiple types
Area hierarchy
Not required
Backbone area
Area boundaries
On segment
At interface
Convergence
Fast
Fast
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IS-IS — Frequently Used Terms
 Area — Corresponds to the level 1 subdomain
 End system — Typically a computer, printer, or other attached
device
 Intermediate system — Router in an IS-IS network
 Neighbor — A physically adjacent router
 Adjacency — A separate adjacency is created for each neighbor
on a circuit and for each level of routing (level 1 and level 2)
on a broadcast circuit.
 Circuit — A single locally attached network
 Link — The communication path between 2 neighbors
 CSNP — Complete sequence number PDU
 PSNP — Partial sequence number PDU
 PDU — Protocol data unit
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IS-IS — Frequently Used Terms (continued)
 Designated IS — The intermediate system in a LAN that is
designated to generate updates on behalf of the nodes in the
LAN
 Pseudo node — When a broadcast subnetwork has n connected
intermediate systems, the broadcast subnetwork itself is
considered to be a pseudo node.
 Broadcast subnetwork — A multi-access subnetwork (such as
Ethernet) that supports the capability of addressing a group of
attached systems with a single PDU
 General topology subnetwork — A topology that is modeled as a
set of point-to-point links, each of which connects 2 systems
 Routing subdomain — A set of intermediate systems and end
systems that are located within the same routing domain
 Level 2 subdomain — The set of all level 2 intermediate
systems in a routing domain
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IS-IS — Protocol Overview
 IS-IS uses SPF for path determination.
 SPF uses cost values to determine the best path to a
destination.
RTR-C
10.0.0.0
Cost: 10
Cost: 10
Cost: 10
Cost: 10
RTR-A
RTR-B
Cost: 10
RTR-A
10.0.0.0: cost 30 via RTR-C
Packet flow
*10.0.0.0: cost 20 via RTR-B
* = Best path
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IS-IS — ISO Network Addressing
 IS-IS uses unique addressing (OSI NSAP addresses) compared
to that of other IP routing protocols.
 Each address identifies the area, system, and sector.
 Routers with common area addresses form L1 adjacencies.
 Routers with different area addresses form L2 adjacencies, if
capable.
 2-layer hierarchy:
 Level 1: Builds the local area topology and forwards traffic to
other areas through the nearest L1/L2 router
 Level 2: Exchanges prefix information and forwards traffic
between areas
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IS-IS — ISO Network Addressing (continued)
 Layer 2 multicast addressing is implemented to support ISIS.
 On Ethernet, the following multicast addresses are
reserved:
 L1 updates use 01-80-C2-00-00-14.
 L2 updates use 01-80-C2-00-00-15.
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IS-IS — Link-State Overview
L1
L2
Area 49.0002
L1/L2
L1/L2
L1
Area 49.0003
L1/L2
L1
Area 49.0001
Alcatel-Lucent Interior Routing Protocols and High Availability
L1
L2
L1/L2
Backbone (level 2) link
Level 1 link
Level 1
Level 2
Level 1/level 2
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92
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IS-IS — NSAP Addressing
IDP
AFI
IDI
DSP
High Order-DSP
System ID
SEL
6
1
variable
Area ID
System Address NSEL
NSAP — Network service access point
IDP — Initial domain part
DSP — Domain specific part
AFI — Authority and format indicator
IDI — Initial domain identifier
(e.g., 49 is local assigned, binary)
High Order-DSP — High Order Domain Specific Part
SEL — N-selector (NSEL)
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IS-IS — Protocol Characteristics
Item
Value
Maximum metric value assignable to a link
Maximum metric value for a path
All L1 IS multicast address
All L2 IS multicast address
SAP for IS-IS on 802.3 LANs
Protocol discriminator for IS-IS
NSAP selector for IS-IS
Sequence modulus
Size of LSP, which all IS routers must be able to handle
Maximum age
Zero life age
Maximum number of area addresses in a single area
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16 777 215
4 261 412 864
01-80-C2-00-00-14
01-80-C2-00-00-15
FE
83
00
232
1492
1200
60
3
94
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IS-IS — Packet Format
 IS-IS packets use layer 2 encapsulation of the media.
 The Ethernet type field is set to 0xFEFE to denote an IS-IS
packet instead of an IP packet.
 The TLV identifies the type of information in the IS-IS
packet.
 IS-IS packets are called PDUs.
Ethernet
header
Type = 0xFEFE
IS-IS header
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IS-IS TLV
Link trailer
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IS-IS — Packet Format Details
 Ethernet destination address:
 01-80-C2-00-00-14 – L1 updates
 01-80-C2-00-00-15 – L2 updates
 Ethernet source address: source router interface MAC
address
 802.3 LLC DSAP and SSAP = FE:FE
 Layer 3 protocol discriminator: 83
Ethernet
header
Type = 0xFEFE
IS-IS header
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IS-IS TLV
Link trailer
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IS-IS — Packet Format Details (continued)
 IS-IS sends PDUs.
 PDUs are encapsulated directly into the layer 2 frame.
 There are 4 types of PDUs:
 Hello (ESH, ISH, and IIH) — Maintain adjacencies
 LSP (link-state packet) — Information about neighbors and
links, generated by all L1 and L2 routers
 PSNP (Partial Sequence Number PDU) — Specific requests and
responses about links, generated by all L1 and L2 routers
 CSNP — Complete list of LSPs exchanged to maintain database
consistency
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Alcatel-Lucent Routing Protocols
Module 7 — Border Gateway Protocol
BGP Scope
 Enables the exchange of routing information between
autonomous systems (AS)
 An AS is a collection of routers that are under a single
administration, which presents a consistent routing
policy.
 Enables the implementation of administrative policies
 BGP has already scaled to:
Large number of ASs
Large number of neighbors
Large volume of table entries
High rate of change
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Autonomous Systems in BGP
AS-65002
AS-65003
• An AS is a group of networks and network equipment under
a common administration.
AS-65001
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• IGP protocols such as OSPF, IS-IS, and RIP run in an AS.
• BGP is used to connect ASs.
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Autonomous Systems in BGP (continued)
 Public autonomous systems:
 Assigned by ARIN or another authority
 Must be used when connecting to other ASs on the Internet.
 Range from 0 to 64 511
 Private autonomous systems:
 Assigned by ISPs (for some clients) and local administrators
 Not allowed to be advertised to other ISPs or on the Internet
 Range from 64 512 to 65 535
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BGP Features
 Path vector protocol:
 Neighbor is any reachable device
 Unicast exchange of information
 Reliability using TCP
 Uses well-known TCP port 179
 Periodic keepalive for session management
 Event-driven
 Robust metrics
 Authentication
 Similar behavior as other TCP/IP applications
 Because BGP peers are not always directly connected, BGP
relies on IGP to route between peers.
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eBGP vs. iBGP Overview
 2 types of BGP sessions are possible.
 The routers may be in different ASs:
 Called external BGP or eBGP
 Typically directly connected, but not mandatory
 Different administrations
 The routers may be in the same AS:
 Called internal BGP or iBGP
 Typically remote, but could be directly connected
 Same administration
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www.alcatel-lucent.com
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