1. Advanced Juniper Networks Routing
Module 1: Open Shortest
Path First (OSPF)
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

2. Advanced Juniper Networks Routing
Module Objectives
Review the basic components of the OSPF Protocol
Discuss the OSPF neighbor hello protocol and adjacency formation process
Examine the function of the Link-State Database (LSDB) and how it contributes routes to the routing table
Look at the different kinds of OSPF packet types
Configure OSPF on a Juniper Networks router
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

3. Link-State Update Packets
Advanced Juniper Networks Routing
Link-State Update Packets
Carry one or more link-state advertisements
Link-state update packets consist of:
OSPF header
(4-byte) Number of advertisements
Link-state advertisements
# of LSAs
LSA Header
LSA Data …
Field length, in bytes 1 2 4 8
Variable
Data
Authentication
Authent- ication type
Check- sum
Area ID
Router ID
Packet length
Type
Version number
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

4. Advanced Juniper Networks Routing
LSA Packet Types
Link-state advertisement packet types:
Router LSAs - Type 1
Network LSAs - Type 2
Summary LSAs - Types 3 and 4
AS external LSAs - Type 5
Group membership LSAs - Type 6
NSSA LSAs - Type 7
External attributes LSAs - Type 8
Opaque LSAs - Types 9, 10, and 11
Each LSA type describes a portion of the OSPF routing domain
Types 6, 8, 9, and 11 are not supported
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

5. Advanced Juniper Networks Routing
LSA Packet Header
Information to uniquely identify the LSA
The 20-byte LSA header consists of:
(2-byte) LS Age
(1-byte) Options
(1-byte) LS Type
(4-byte) Link-State ID
(4-byte) Advertising Router
(4-byte) LS Sequence Number
(2-byte) LS Checksum
(2-byte) Length
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

6. Advanced Juniper Networks Routing
Router LSA (Type 1)
Originated by each router in an area
Describes the state and cost of the router’s interfaces
Router LSAs consist of LSA header plus:
(1-byte) Five 0 bits followed by the V, E and B bits
(1-byte) 0 bits
(2-byte) Number of Links
(4-byte) Link ID
(4-byte) Link Data
(1-byte) Link Type
(1-byte) Number of TOS Metrics
(2-byte) Metric
(4-byte) Additional TOS Data
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

7. Advanced Juniper Networks Routing
Router LSA Example
show ospf database router extensive
OSPF link state database, area
Type ID Adv Rtr Seq Age Opt Cksum Len
Router * x x2 0xd45b 60
bits 0x3, link count 3
id , data , type PointToPoint (1)
TOS count 0, TOS 0 metric 1
id , data , type Stub (3)
id , data , type Stub (3)
TOS count 0, TOS 0 metric 0
Gen timer 00:30:56
Aging timer 00:44:13
Installed 00:15:47 ago, expires in 00:44:13, sent 00:15:47 ago
Ours
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

8. Advanced Juniper Networks Routing
Network LSA (Type 2)
Originated by designated routers (DR)
Describes all routers attached to a network segment
Network LSAs consist of LSA header plus:
(4-byte) Network Mask
(4-byte) Attached Router
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

9. Advanced Juniper Networks Routing
Network LSA Example
show ospf database network extensive
OSPF link state database, area
area
Type ID Adv Rtr Seq Age Opt Cksum Len
Network x x2 0x
mask
attached router
attached router
Aging timer 00:46:27
Installed 00:13:32 ago, expires in 00:46:27, sent 1w5d 01:07:09 ago
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

10. Advanced Juniper Networks Routing
Summary LSA (Type 3)
Originated by area border routers (ABR)
Describes all routers attached to a multiaccess segment
Summary LSA (Type 3) consists of LSA header plus:
(4-byte) Network Mask
(1-byte) 0 bits
(3-byte) Metric
(1-byte) TOS
(3-byte) TOS Metric
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

11. Advanced Juniper Networks Routing
Summary LSA Example
show ospf database netsummary extensive
OSPF link state database, area
Type ID Adv Rtr Seq Age Opt Cksum Len
Summary x x2 0x
mask
TOS 0x0, metric 1
Aging timer 00:43:08
Installed 00:16:49 ago, expires in 00:43:09, sent 1w5d 01:08:42 ago
Summary x x2 0x49f9 28
mask
Aging timer 00:37:25
Installed 00:22:33 ago, expires in 00:37:25, sent 1w5d 01:08:42 ago
Summary * x x2 0x87c6 28
TOS 0x0, metric 2
Gen timer 00:14:18
Aging timer 00:34:33
Installed 00:25:27 ago, expires in 00:34:33, sent 00:25:27 ago
Ours
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

12. Advanced Juniper Networks Routing
Summary LSA (Type 4)
Originated by area border router (ABR)
Describes the destination of an ASBR
Summary LSA (Type 4) consists of LSA header plus:
(4-byte) Network Mask
(1-byte) 0 bits
(3-byte) Metric
(1-byte) TOS
(3-byte) TOS Metric
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

13. ASBR Summary LSA Example
Advanced Juniper Networks Routing
ASBR Summary LSA Example
show ospf database asbrsummary extensive
OSPF link state database, area
Type ID Adv Rtr Seq Age Opt Cksum Len
ASBRSum * x x2 0x
mask
TOS 0x0, metric 1
Gen timer 00:48:43
Aging timer 00:58:43
Installed 00:01:16 ago, expires in 00:58:44, sent 00:01:16 ago
Ours
ASBRSum x x2 0x3b07 28
Aging timer 00:35:22
Installed 00:24:35 ago, expires in 00:35:23, sent 1w5d 01:10:44 ago
ASBRSum * x x2 0x79d3 28
TOS 0x0, metric 2
Gen timer 00:14:36
Aging timer 00:32:30
Installed 00:27:29 ago, expires in 00:32:31, sent 00:27:29 ago
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

14. Advanced Juniper Networks Routing
AS External LSA (Type 5)
Originated by AS boundary routers (ASBR)
Describes destination external to the OSPF network
Two types of external destinations (Type 1 external and Type 2 external)
AS external LSAs consist of LSA header plus:
(4-byte) Network Mask
E-bit (0 = Type 1 external; 1 = Type 2 external) followed by seven 0 bits
(3-byte) Metric
(4-byte) Forwarding Address
(4-byte) External Route Tag
(4-byte) Optional TOS fields
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

15. Advanced Juniper Networks Routing
External LSA Example
show ospf database extern extensive
OSPF external link state database
Type ID Adv Rtr Seq Age Opt Cksum Len
Extern * x x2 0x
mask
Type 1, TOS 0x0, metric 20, fwd addr , tag
Gen timer 00:00:32
Aging timer 00:28:01
Installed 00:31:59 ago, expires in 00:28:01, sent 00:31:58 ago
Ours
Extern x x2 0x
Aging timer 00:28:42
Installed 00:31:15 ago, expires in 00:28:42, sent 00:31:15 ago
Extern x x2 0xcc54 36
Aging timer 00:38:33
Installed 00:21:25 ago, expires in 00:38:33, sent 00:21:25 ago
Extern x x2 0x
Aging timer 00:31:34
Installed 00:28:25 ago, expires in 00:31:32, sent 00:28:25 ago
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

16. NSSA External LSA (Type 7)
Advanced Juniper Networks Routing
NSSA External LSA (Type 7)
Similar to AS external LSAs, but NSSA LSAs have only area flooding scope
Selectively translated into AS external LSAs (Type 5) at the NSSA border
N/P bit in the Type-7-LSA’s option field indicates whether the Type-7-LSA should be translated
N/P = 1 translate (propagate)
N/P = 0 do not translate
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

17. Advanced Juniper Networks Routing
NSSA LSA Example
show ospf database nssa extensive
OSPF link state database, area
area
Type ID Adv Rtr Seq Age Opt Cksum Len
NSSA x x8 0x7c19 36
mask
Type 1, TOS 0x0, metric 20, fwd addr , tag
Aging timer 00:32:47
Installed 00:27:12 ago, expires in 00:32:41, sent 1w5d 01:13:35 ago
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

18. Advanced Juniper Networks Routing
Opaque LSA (Types 9 – 11)
Allows for the future extensibility of OSPF
Opaque LSAs consist of a standard LSA header followed by application-specific information
The information field can be used directly by OSPF or by other applications
Consists of a standard LSA header followed by a 32-bit application-specific information field
The difference is in flooding scope
Type 10 are used for MPLS Traffic Engineering
Types 9 and 11 are not currently supported
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

19. Advanced Juniper Networks Routing
Sample OSPF Database
show ospf database
OSPF link state database, area
Type ID Adv Rtr Seq Age Opt Cksum Len
Router * x x2 0xc
Router x f x2 0x3bfd 72
Router x x2 0xd3db 48
Network x x2 0x5e7b 32
Summary * x x2 0xd31c 28
Summary * x x2 0xc
Summary * x x2 0x24a2 28
Summary * x x2 0x
Summary * x x2 0xe56d 28
Summary * x x2 0xaba2 28
ASBRSum * x x2 0x1a41 28
ASBRSum * x x2 0xd77a 28
ASBRSum * x x2 0x9fae 28
OSPF external link state database
Extern * x x2 0x
Extern x x2 0xe
Extern x x2 0xa
Extern x x2 0x
Extern x x2 0xc
Extern x x2 0x
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

20. Copyright © 2001, Juniper Networks, Inc.
LSA Flooding Scopes
External
Routes
Backbone
( )
Area 0
LSA 2
Area 0
LSA 5
Area 0
LSA 1
Area 3
LSA 5
Area 1
LSA 3
Area 2
LSA 3
Area 3
LSA 3
Area 3
LSA 4
Area 1
LSA 1
Area 1
LSA 2
Area 2
LSA 1
Area 2
LSA 2
Area 3
LSA 1
Area 3
LSA 2
Area 0
LSA 3
Area 0
LSA 3
Area 0
LSA 4
Area 0
LSA 3
Area 0
LSA 4
Area 0
LSA 4
Area 1
LSA 3
Area 2
LSA 3
Area 3
LSA 4
Area 1
LSA 3
Area 3
LSA 4
Area 0
LSA 5
Area 2
LSA 3
Area 3
LSA 3
Area 0
LSA 5
Area 3
LSA 3
Area 0
LSA 5
Area 3
LSA 5
Area 3
LSA 5
Area 3
LSA 5
External
Routes
Area 1
Area 2
Area 3
Copyright © 2001, Juniper Networks, Inc.

21. Copyright © 2001, Juniper Networks, Inc.
OSPF Router-ID
Each OSPF router selects a 32-bit value to use as its Router-ID
The Router-ID is populated within the LSAs that each router sends out
The link-state database uses this information for run the SPF algorithm
When RPD initiates, the primary interface of the router is chosen as the Router-ID
A value can be permanently set within [edit routing-options]
[edit routing-options]
set router-id
Copyright © 2001, Juniper Networks, Inc.

22. Copyright © 2001, Juniper Networks, Inc.
OSPF Cost
Cost, or metric, of an interface indicates the overhead required to send packets out a particular interface
Default OSPF cost for all links is 10**8/bandwidth (bps)
All links with a bandwidth greater than 100M will have a cost of 1
Cost calculation results in a value <1, so it is rounded
Cost can be set on a per interface basis
[edit protocols ospf]
show
area {
interface so-0/0/0.0 {
metric 12; }
interface at-1/0/1.100 {
metric 73;
Copyright © 2001, Juniper Networks, Inc.

23. Copyright © 2001, Juniper Networks, Inc.
Reference Bandwidth
The 10**8 value in the cost calculation can be changed
Automatically alters the cost of interfaces
Allows for a consistent change across all interfaces
Use the reference-bandwidth command within [edit protocols ospf]
[edit protocols ospf]
set reference-bandwidth 1g
show
reference-bandwidth 1g;
area {
interface so-0/0/0.0 {
metric 12; }
interface at-1/0/1.100;
Copyright © 2001, Juniper Networks, Inc.

24. Effects of Altering Metrics
Advanced Juniper Networks Routing
Effects of Altering Metrics
Metric values are advertised in Type 1 or Type 2 LSAs and populate link-state database
As each router runs SPF algorithm, each LSA is examined individually for cost of outgoing interface
That cost is used in the final metric calculation
Routers can disagree about the cost on a network link
HongKong sees a cost of 45 to reach Amsterdam
Amsterdam sees a cost of 60 to reach HongKong
HongKong
SanJose
Montreal
Amsterdam 5 10 15 20 25 30
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

25. Copyright © 2001, Juniper Networks, Inc.
OSPF Authentication
Authentication occurs within an individual area
Three types are supported: none, simple, and MD5
By default, the authentication type is set to none
Effectively means no authentication is performed
A plain-text password is used with type simple
Each interface requires an authentication key
Multiple interfaces can use the same key
Keys are always encrypted in the configuration
[edit protocols ospf]
show
area {
authentication-type simple;
interface ge-0/0/0.0 {
authentication-key "$9$-TbwgPfzn6A"; }
Copyright © 2001, Juniper Networks, Inc.

26. Copyright © 2001, Juniper Networks, Inc.
MD5 Authentication
Includes an encrypted checksum with all packets
Provides better security than type simple
Each interface requires an authentication key
Multiple interfaces can use the same key
Keys are always encrypted in the configuration
Each key requires a key-id value
If omitted, a value of 1 is used
[edit protocols ospf]
show
area {
authentication-type md5;
interface so-0/3/1.0 {
authentication-key "$9$ul8b0IcyrvL7VKM" key-id 10; }
Copyright © 2001, Juniper Networks, Inc.

27. Copyright © 2001, Juniper Networks, Inc.
Virtual Links
Virtual links can connect remote OSPF areas together
Often used for an area not physically connected to the backbone
Can also be used for a discontiguous backbone
Configuration always occurs within area
Creates a virtual ABR out of the remote router
“Tunnels” packets through a transit area
Both ends must configure the link towards each other
Virtual Link
Area 0
Area 1
Area 2
Copyright © 2001, Juniper Networks, Inc.

28. Virtual Link Configuration
The area to be “tunneled” through is the transit-area
The router at the far end of the link is the neighbor-id
This is the 32-bit router ID
Once configured, the virtual link appears as an operational OSPF interface
[edit protocols ospf]
show
area {
interface fe-0/2/2.0; }
area {
virtual-link neighbor-id transit-area ;
show ospf interface
Interface State Area DR ID BDR ID Nbrs
vl PtToPt
show ospf neighbor
Address Interface State ID Pri Dead
vl Full
Copyright © 2001, Juniper Networks, Inc.

29. Copyright © 2001, Juniper Networks, Inc.
Overload Bit
Used to advertise information to neighbors, but not be used for transit traffic
Sets metrics to on all transit links
Can be set permanently or with a timeout value
Timer is between 60 and 1800 seconds
Timer only runs after RPD starts
[edit protocols ospf]
show
overload;
area {
interface so-0/0/0.0;
interface ge-0/1/0.0; }
show ospf database router extensive
OSPF link state database, area
Type ID Adv Rtr Seq Age Opt Cksum Len
Router x x2 0x540b 60
id , data , type PointToPoint (1)
TOS count 0, TOS 0 metric 65535
Copyright © 2001, Juniper Networks, Inc.

30. Multi-Area OSPF Configuration
Advanced Juniper Networks Routing
Multi-Area OSPF Configuration
Configured at the [edit protocols] hierarchy level
List each interface and area separately
protocols {
ospf {
area <area-id> {
interface <interface-name>; }
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)

31. Advanced Juniper Networks Routing
Review Questions
During this module we discussed:
The JUNOS software configuration options for BGP.
The default behavior of the BGP routing protocol with regard to the “movement” (use and advertising) of BGP routes through the router.
How the BGP attributes play a role in the process of choosing routes to use and advertise through BGP.
When BGP next hop reachability was an issue and how BGP routes find their next-hops.
The available options for handling IBGP scalability issues such as the number of peer sessions that must be maintained.  
Copyright © 2001, Juniper Networks, Inc.
Module 1: Open Shortest Path First (OSPF)