Advanced OSPF & BGP

By Ashlan Chidester

Routing Basics and OSPF

Routing Basics

This track will cover the fundamental concepts of routing, including the role of routing protocols, the differences between static and dynamic routing, and the key components of a routing table. You will learn how routers make forwarding decisions and the importance of routing metrics in determining the best path.

OSPF

This section will provide an in-depth introduction to the Open Shortest Path First (OSPF) routing protocol. You will learn about the OSPF architecture, the different OSPF areas, and the OSPF neighbor and adjacency formation process. You will also explore specific OSPF concepts such as the Dijkstra algorithm, link-state advertisements (LSAs), and the OSPF designated router (DR) election.

Scaling OSPF

As networks grow in size and complexity, it becomes necessary to scale the OSPF protocol. This module will cover techniques for scaling OSPF, including the use of OSPF areas, virtual links, and route summarization. You will learn how to design and implement OSPF networks that can efficiently handle large-scale topologies.

OSPF Troubleshooting

Troubleshooting OSPF networks is a critical skill for network administrators. In this section, you will learn common OSPF troubleshooting techniques, such as analyzing OSPF neighbor relationships, interpreting OSPF debug output, and identifying and resolving OSPF routing issues.

Lab 1: OSPF

This hands-on lab will provide you with the opportunity to configure and troubleshoot OSPF in a simulated network environment. You will practice setting up OSPF, verifying the protocol's operation, and resolving common OSPF-related problems.

BGP Protocol and E-BGP

BGP Protocol

This track will introduce you to the Border Gateway Protocol (BGP), the de facto standard for inter-domain routing on the internet. You will learn about the BGP architecture, the different BGP message types, and the BGP decision process.

Policy Routing Mechanisms

BGP provides a rich set of policy routing mechanisms that allow network administrators to control the flow of traffic through their networks. In this section, you will explore various BGP policy tools, such as route maps, community attributes, and AS-path manipulation.

E-BGP Concepts

The focus will then shift to External BGP (E-BGP), which is used to exchange routing information between autonomous systems (ASes). You will learn about E-BGP peering, route advertisement, and the role of the BGP next-hop attribute.

E-BGP Troubleshooting

Troubleshooting E-BGP networks is essential for maintaining reliable inter-domain connectivity. This module will cover common E-BGP troubleshooting techniques, including analyzing BGP neighbor states, interpreting BGP debug output, and identifying and resolving E-BGP routing issues.

Lab 2: E-BGP

In this hands-on lab, you will configure and troubleshoot E-BGP in a simulated network environment. You will practice setting up E-BGP peering, verifying the protocol's operation, and resolving common E-BGP-related problems.

Review of Tracks 1-2 and I-BGP

Review of Concepts from Tracks 1-2

This section will provide a comprehensive review of the key concepts covered in the first two tracks, including routing basics, OSPF, and E-BGP.

I-BGP

The focus will then shift to Internal BGP (I-BGP), which is used to exchange routing information within an autonomous system. You will learn about the I-BGP architecture, the role of the I-BGP full mesh, and the concept of route reflection.

I-BGP Concepts

In this module, you will explore specific I-BGP concepts, such as the I-BGP decision process, the handling of IBGP-learned routes, and the use of the I-BGP next-hop attribute.

...and much more! 

Thank you,

 

Ashlan

• Language: English
• Publisher: MC Inc
• Release date: Apr 16, 2024
• ISBN: 9798224952625

Ashlan Chidester

Thank you!

Book preview

Image 1

TRANSFORMING COMMUNICATIONS THROUGH BROADBAND INNOVATION

OSPF and BGP

Advanced

Ashlan Chidester

Agenda

Track1: Routing Basics and OSPF

•

Routing Basics

•

OSPF

•

OSPF Introduction

•

-specific OSPF Concepts

•

Scaling OSPF

•

OSPF Troubleshooting

•

Lab 1: OSPF

Track2: BGP Protocol and E-BGP

•

BGP Protocol

•

Policy Routing Mechanisms

•

-Specific E-BGP Concepts

•

E-BGP Troubleshooting

•

Lab 2: E-BGP

2

Agenda

Track3: Review of tracks 1-2 and I-BGP

•

Review of concepts from tracks 1-2

•

I-BGP

•

I-BGP Concepts

•

I-BGP Troubleshooting

•

Lab 3: I-BGP Full Mesh

•

Lab 4: I-BGP Route-Reflector

3

Agenda

Track4: I-BGP and -Specific Implementation

•

-specific OSPF Implementation

•

-specific I-BGP Implementation

•

Inter-IP PoP

•

Intra-IP PoP

•

-specific E-BGP Implementation

•

ISP

•

Partner

•

VSO

•

Putting it all together – OSPF/E-BGP/I-BGP Troubleshooting

•

Lab 5: Troubleshooting

•

Routing Futures

•

Backbone

4

Image 2

TRANSFORMING COMMUNICATIONS THROUGH BROADBAND INNOVATION

Routing Basics

Router Basics

•

A router utilizes routing protocol(s) to build the routing table

•

Without a routing protocol, the router cannot forward packets

•

The router’s job is to

1. Determine if the packet's destination is reachable 2. Determine the next hop toward the destination, and the interface through which that next hop is reachable

3. Rewrite the Media Access Control (MAC) header on the packet so it will successfully reach its next hop

•

The routing table and other data structures are used to make forwarding decisions

6

Routing Table

•

A router maintains multiple routing tables

•

Main Routing Table contains the best route information consolidated from all protocols running on the router

• Populates a route cache when the first packet for a specific destination needs to be forwarded

• This consumes memory and processor resources

• Cache maintenance is a demanding task

• Show ip route displays the contents of the main routing table

•

Protocol Tables: some protocols maintain separate tables where the protocol specific information is maintained This information is then merged with the main routing table

• OSPF database (show ip ospf database)

• BGP table (show ip bgp)

7

Routing Table

•

CEF (Cisco Express Forwarding): FIB and Adjacency Table on RP

• Introduced in IOS 111

• De-couples forwarding information from next hop adjacency info

• FIB (Forwarding Information Base) makes IP destination prefix-based switching decisions

• Adjacency table maintains Layer 2 next-hop addresses for all FIB entries

• FIB contains a mirror image of the forwarding information contained in the routing table

• Show ip cef displays the contents of the FIB

8

Routing Table

•

D-CEF (Distributed CEF): Copy of FIB and Adjacency Table on every line card

• Available on 76xx and 75xx platform

• Forwarding decision made locally on D-CEF enabled line cards Protocol

Table

D-FIB

Protocol

D-FIB

Routing Table

FIB

Table

D-FIB

Protocol

Table

9

Routing Table

•

How does the router determine which information to use when there are multiple sources of routing information?

•

Subnet Mask  longest subnet mask is preferred

• 1010100/24 is preferred over 10000/8

•

Administrative distance  lowest administrative distance is preferred

• E-BGP (admin dist=20) is preferred over OSPF (admin dist=110) 10

Administrative Distance

The router will always pick the route whose routing protocol has the lowest administrative distance

Route Source

Default Distance

Connected Interface/Static

0

Route pointing to Outbound

Interface

Static Route pointing to

1

Gateway IP address

External BGP

20

OSPF

110

IS-IS

115

RIP

120

Internal BGP

200

Unknown

255

11

Routing Table

LAB-7609-01#sh ip route

Codes: C - connected, S - static, 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, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2

ia - IS-IS inter area, * - candidate default, U - per-user static route o - ODR, P - periodic downloaded static route Gateway of last resort is 99426 to network 0000

16000/24 is subnetted, 2 subnets

B 16110 [200/5] via 21110, 2w6d

B 16120 [200/5] via 21110, 2w6d

2000/30 is subnetted, 5 subnets

C 2114 is directly connected, FastEthernet2/10

O 2228 [110/101] via 994210, 5d06h, GigabitEthernet3/3

O 2118 [110/110] via 2115, 5d06h, FastEthernet2/10

O 22212 [110/101] via 2115, 5d06h, FastEthernet2/10

O 21112 [110/150] via 99426, 5d06h, GigabitEthernet3/4

[110/150] via 99422, 5d06h, GigabitEthernet5/1

O E1 996615/32 [110/120] via 994210, 5d06h, GigabitEthernet3/3

[110/120] via 2115, 5d06h, FastEthernet2/10

C 99680/29 is directly connected, FastEthernet2/13

Overlapping

S 99680/21 is directly connected, Null0

O 996614/32 [110/101] via 2115, 5d06h, FastEthernet2/10

entries in the

routing table If

destination is

99681, which

entry is used to

forward the

packet?

12

Routing Table

LAB-7609-01#sh ip route | include 99680

C 99680/29 is directly connected, FastEthernet2/13

S 99680/21 is directly connected, Null0

LAB-7609-01#sh ip route 99680 255255255248

Routing entry for 99680/29

Known via connected, distance 0, metric 0 (connected, via interface) Redistributing via bgp 18566

Advertised by bgp 18566 route-map connected->bgp Routing Descriptor Blocks:

* directly connected, via FastEthernet2/13

Route metric is 0, traffic share count is 1

LAB-7609-01#sh ip route 99680 2552552480

Routing entry for 99680/21

Known via static, distance 1, metric 0 (connected) Tag 20

Redistributing via bgp 18566

Advertised by bgp 18566 route-map static->bgp Routing Descriptor Blocks:

* directly connected, via Null0

Route metric is 0, traffic share count is 1

Route tag 20

13

Routing Table vs BGP Table LAB-7609-01#sh ip bgp | include 9968

*> 99680/29 0000 0 120 32768 i

* i99680/21 99667 0 120 0 I LAB-7609-01#sh ip bgp 99680 255255255248

BGP routing table entry for 99680/29, version 7807715

Paths: (1 available, best #1, table Default-IP-Routing-Table) Advertised to update-groups:

3 4

Local

0000 from 0000 (99666)

Origin IGP, metric 0, localpref 120, weight 32768, valid, sourced, best Community: 18566:120 18566:1022

LAB-7609-01#sh ip bgp 99680 2552552480

BGP routing table entry for 99680/21, version 83098

Paths: (2 available, best #2, table Default-IP-Routing-Table) Advertised to update-groups:

1 3 4

Local

99667 (metric 51) from 99667 (99667)

Origin IGP, metric 0, localpref 120, valid, internal Community: 18566:20 18566:120 18566:1022

Local

0000 from 0000 (99666)

Origin IGP, metric 0, localpref 120, weight 32768, valid, sourced, best Community: 18566:20 18566:120 18566:1022

14

BGP Table

LAB-7609-01#sh ip bgp nei 99999921 advertised-routes | include 996

BGP table version is 7747713, local router ID is 99666

*>i8888880/24 996614 0 120 0 i

*> 99600/16 0000 120 32768 i

*> 99610/24 0000 0 120 32768 i