1. Unicast Routing in IPv6
Babu Ram Dawadi

2. Index What is a unicast routing protocol? Discuss about RIPng
What are the Routing Table Entries of RIPng
Explain RIPng Message Format
What are different timers of RIPng
What is OSPF?
How do OSPF routers on the same link establish adjacencies? What does it mean to be adjacent? GWE.
How do OSPF routers synchronize their Link State Databases? GWE.
How to calculate the best route in OSPF? GWE.
Learn how to see the above processes using ospfd, and ospf6d.

3. Unicast Routing Protocol
Unicast routing is a process that enable sender to send an unicast IP packets to the destination node.
1 router or more intermediate routers may be used, depending to the destination of the node. (Figure 1)
Unicast routing protocol is a set of rules of forwarding unicast traffic from a source to a destination on an internetwork.
The router is using only 1 port to forwards the received unicast packet
Fig. 1. Unicast Routing

4. Unicast Routing Protocol
Unicast Routing Protocol consists of:
RIP (Routing Information Protocol)
OSPF (
BGP
They each serve a different purpose.
Routing
Interior
Exterior
RIP
OSPF
BGP
Fig. 2. Types of Unicast Routing Protocol

5. RIPng (RFC 2080)
Based on Distance Vector algorithm known as bellman ford algorithm
Router keeps the following entries in the routing table
IPv6 Route
Address prefix and prefix length of the destination address
Next Hop Address
The IPv6 Address (link-local) of the first router along the path
Next Hop Interface
The physical interface used to reach the next hop
Metric
Number indicating the total distance to the destination. RIPng advertizes directly connected routes with the configured outgoing metric of 1

6. RIPng routing table Timer Route change flag Route Source
Amount of time since the information about the route was last updated
Route change flag
Set to control triggered routing updates
Route Source
Entity to provide route information eg: Ripng, OSPF etc..

7. RIPng Message Format UDP based protocol using udp port number 521
IPv6 Header
UDP Header
RIPng Header
RTE1
RTE2
RTE3
………
RTEn
20 Bytes/RTE
1: Request
2: Response
Command 1: ask system to send all or part of its routing table
Command 2: sends an update message containing all or parts of the senders routing table.
Command 1B
Version 1B
Unused 2B

8. Routing Table Entry (RTE)
RIPng header is followed by one or more routing table entries (format of Routing table entry)
16 B ….
IPv6 Prefix
2 B
Route Tag
1 B
Prefix Length
1 B
Metric(1-16)

9. RTE..
Route Tag
It may be used to carry additional information about a route learned from another routing protocol eg: BGP
The number of RTEs within single updates depends on the MTU of the medium between two neighboring routers
No of RTEs=[INT(MTU-IPv6 Hdr len-UDP Hdr len -RIPng Hdr len) / RTE-Size]
Timers
RIPng uses different timers to control updates of the routing information
Update timer
By default, every 30 seconds, RIPng process wakesup on each interface to send an unsolicited routing response to the neighboring routers

10. Timer Timeout Timer Garbage collection timer (hold down timer)
Each time a route entry is updated and the timeout timer is reset to zero
If the route entry reaches 180 secs (default), without another update, it is considered to have expired, metric set to 16 and garbage collection process starts
Garbage collection timer (hold down timer)
Set to 120 secs (default) that have timeout or been received with a metric of 16 after expiration, the route entry finally be removed from the routing table.

11. Fig. 3. Interior Routing Protocol
OSPF
The difference between intra-domain and inter-domain (Fig. 2.)
Routing within the same AS (Autonomous System) is referred to as intra-domain.
Routing in the different AS (Autonomous System) is referred to as inter-domain.
OSPF is an interior routing protocol
Intra-domain routing protocol
a) Intra-domain
b) Inter-domain
Fig. 3. Interior Routing Protocol

12. OSPF Header 40Byte 16 Byte IPv6 Header NH: 89 OSPF Header OSPF Message
RouterID 4B
Version 1B
AreaID 4B
Packet Type 1B
Checksum 2B
Packet Length 2B
Instance ID 1B
Unused 1B

13. OSPF Process
Link State routing
Each node within the autonomous system has the information about the entire topology.
Each node in the domain build up the routing table using Dijkstra’s algorithm.
Link State Database (LSDB) contains link state advertisement is send to every router in the same domain.
Each router will be updated with the latest copy of LSDB
Based on the LSDB, router creates a Shortest Path First (SPF) tree
Using Dijkstra’s a Algorithm
A routing table can be derived from the SPF tree which contains the best route to each router.

14. Fig. 4. Types of OSPF Packet
Types of OSPF Packets
OSPF Packets
HELLO
Database
Description
Link State
Request
Update
Acknowledgement
Router Link
0x2001
Network Link
0x2002
Inter-Area-Prefix
LSA
0x2003
Inter-Area-Router
0x2004
AS-External-LSA
0x4005
Type 1
Type 2
Type 3
Type 4
Type 5
Group-
Membership-LSA
0x2006
Type-7-LSA
0x2007
Link-LSA
0x0008
Intra-Area-Prefix
Fig. 4. Types of OSPF Packet

15. How do OSPF routers on the same link establish adjacencies?
What does it mean to be adjacent? GWE.

16. OSPF- Forming Adjacencies
OSPF routers on the same link establish adjacencies
Using Hello packet
An OSPF router need to go through 7 steps from no connection to full adjacency when it is first initialized.
Down State
Init State
Two Way state
Exstart
Exchange State
Loading State
Full Adjacency

17. OSPF- Forming Adjacencies (cont)
Down State
None
No information has yet been exchanged.
Init State
Hello Packet
(Type 1)
Routers send hello packets at regular intervals to establish relationships.
Two-way
State
Hello Packet
(Type 1)
A router sees itself in a hello packet.
Hello Packet
(Type 1)
Exstart
Routers negotiate master/slave relationship by comparing their router id using hello packets.
Exchange
State
Database Description
(Type 2)
Neighbors start communicating their link-state information with the others.
Loading
State
Link State Request
Link State Update
Link State Acknowledgement
(Type 3,4,5)
The router has the initial information of each route, they may request for more complete information.
Full
All
(Type 1,2,3,4,5)
Routers are fully adjacent.

18. OSPF- Forming Adjacencies (cont)
Processing of Hello packet
Fig. 5. Processing a Hello Packet
(Reference: IPv6 Essential Pg.169)

19. OSPF- Forming Adjacencies (cont)
The first OSPF neighbor is Down state. It means that no information (hellos) has been received from this neighbor. But it still can send Hello message to its neighbours
Router 2 has received a hello packet from its neighbor, but the receiving router's ID was not included in the hello packet
Router1 has seen the Router 2’s hello packet which had included its own Router ID within the received hello packet's neighbor field
Router2 also has received the Router 1’s hello packet which had also included its own Router ID within the received hello packet's neighbor field
Forming an adjacency
Phases
Packet type involved
At this state, a router decides whether to become adjacent with this neighbor.
The decision on adjacencies is always depend on the link media. (Types of network)
Point to Point
No DR/BDR is needed or used because
because only 2 neighbour routers.
Broadcast Multiple Access
-DR and BDR are elected.
Non-Broadcast Multiple Access
-DR and BDR are elected
To Be Continue...
Time
Fig. 6. Forming an Adjacencies – Part I
(Reference: IPv6 Essential Pg.170)

20. OSPF- Forming Adjacencies (cont)
Types of Network:
Broadcast Multiple Access
Ethernet, Token Ring
Point to Point
PPP, HDLC
Non Broadcast Multiple Access (NBMA)
X.25, Frame Relay
Fig. 7. Types of Network

21. OSPF- Forming Adjacencies (cont)
When DR and BDR are elected, we can say that the adjacencies was established.
The DR and BDR are elected based on several criteria
DR – with highest router ID
BDR – with second highest router ID
Priority 0 will never be DR or BDR
If priorities are same, the higher Router ID is elected.
If DR fails, BDR becomes DR, and new BDR is elected.
After adjacent, the routers already created reliable channels to their neighbors.
These reliable channels is important for the routers to exchange Link State Database (LSDB) with the neighbors..

22. How do OSPF routers synchronize their Link State Databases?

23. OSPF - Link State Databases
The Router 1 is attempted to start the Exchange because “he” might thought that “he” has the highest Router ID
When the routers have elected DR and BDR, the databases need to get synchronized
Routers enter ExStart
Decide who is the Master and Slave.
Router with the Highest ID will become Master and only this router can increment the sequence number
The Master/Slave election is on a per-neighbor basis
Master/Slave election is irrelevant to DR/BDR election for a network.
But Router 2 will reply “No”. I will start the Exchange State first, because I have a higher Router ID
After the election of Master and Slave, the routers start exchange database descriptor (DBD) packets.
!It might logic to conclude
that the DR/BDR with the
highest Router ID will become
the master during this process of
master/slave election.
!But your DR/BDR
election might be purely
based on the
higher priority
configure
on router
Each DBD packet has a sequence number which can be incremented only by master and explicitly acknowledged by slave
DBD contain link-state advertisement (LSA) headers only and describe the contents of the entire link-state database
In this state, the actual exchange of link state information occurs
Routers are fully adjacent with each other. All the router and network LSAs are exchanged and the routers' databases are fully synchronized.
Based on the information provided by the DBDs, routers send link-state request packets
The neighbor then provides the requested link-state information in link-state update packets
Fig. 7. Forming an Adjacencies-Part II
(Reference: IPv6 Essential Pg.170)

24. OSPF – Database Description (DBD) Packet
OSPF Packet Type 2
Database Description Packet
Database Description fields:
I bit = Init bit
M bit = More bit
MS bit = Master / Slave bit

25. OSPF – Database Description (DBD) Packet
I bit is set to1
Indicate that this is First DBD packet send by this router
This packet contain no data.
M bit is set to 1
Indicate that there are more DBD packets to follow
MS bit is set to 1
Indicate that this router ( ) declares itself to be Master

26. OSPF – Database Description (DBD) Packet
I bit is set to 1
Indicate that this is First DBD packet send by this router
This packet contain no data.
M bit is set to 1
Indicate that there are more DBD packets to follow
MS bit is set to 1
Indicate that this router ( ) declares itself to be Master
Empty

27. OSPF – Database Description (DBD) Packet
I bit is set to 0
Indicate that this is NOT First DBD packet send by this router
It contain database description of router
M bit is set to 0
Indicate that there are no more DBD packets to send
All database descriptions have been sent
MS bit is set to 0
Indicate that this router ( ) declares itself to be Slave

28. OSPF – Database Description (DBD) Packet
I bit is set to 0
Indicate that this is NOT First DBD packet send by this router
It contain database description of router
M bit is set to 1
Indicate that there are more DBD packets to send
The database descriptions will still be sent
MS bit is set to 1
Indicate that this router ( ) is still a Master

29. OSPF – Database Description (DBD) Packet
The router is still sending
a empty packet even it had no data
description to send. This empty packet
is help to keep the DBD sequence number
matched because router
is still sending the DBD packet.
I bit is set to 0
Indicate that this is NOT First DBD packet send by this router
It contain database description of router
M bit is set to 0
Indicate that there are no more DBD packets to send
All database descriptions have been sent
MS bit is set to 0
Indicate that this router ( ) is still a Slave
Empty

30. OSPF – Database Description (DBD) Packet
I bit is set to 0
Indicate that this is NOT First DBD packet send by this router
It contain database description of router
M bit is set to 0
Indicate that there are no more DBD packets to send
All database descriptions have been sent
MS bit is set to 1
Indicate that this router ( ) is still a Master

31. OSPF – Database Description (DBD) Packet
Now, both router has nothing more to send
All the router now enter to the
Loading State
I bit is set 0
Indicate that this is NOT First DBD packet send by this router
M bit is set 0
Indicate that there are no more DBD packets to send
All database descriptions have been sent
MS bit is set 0
Indicate that this router ( ) is still a Slave
Empty

32. OSPF – Link State Request Packet
OSPF Packet Type 2
Link State Request Packet
Multiple requests can be sent
using a single packet.
(Reference IPv6 Essential pg.172)

33. OSPF – Link State Update Packet (0x2001)
OSPF Packet Type 4
Link State Request Packet
Link State Update Packet Type 0x2001
Router-LSA

34. OSPF – Link State Update Packet (0x2002)
OSPF Packet Type 4
Link State Request Packet
Link State Update Packet Type 0x2002
Network-LSA

35. OSPF – Link State Update Packet (0x4005)
OSPF Packet Type 4
Link State Request Packet
Link State Update Packet Type 0x4005
AS-External-LSA

36. OSPF – Link State Update Packet (0x0008)
OSPF Packet Type 4
Link State Request Packet
Link State Update Packet Type 0x0008
Link-LSA
Purpose: List all IPv6 Prefix attached to the link

37. OSPF – Link State Update Packet (0x2009)
Each Link Update Request must be
Link State Acknowledgment Packet
Acknowledged by
OSPF Packet Type 4
Link State Request Packet
Link State Update Packet Type 0x2009
Intra-Prefix-LSA

38. OSPF – Link State Acknowledgement Packet
OSPF Packet Type 5
Link State Acknowledgement Packet
All the router now enter the
Full State
Hello packet is still sending
to keep the adjacency alive

39. How to calculate the best route in OSPF? GWE.

40. Calculate the best route in OSPF
Now every router has a complete Link State Database
They are ready to create their own routing table
From the Link State information, router can compute shortest paths delivery tree.
Using Dijkstra’s Algorithm
Finally, it is time for Dijkstra!

41. OSPF – Dijkstra’s Algorithm
Depicted in Fig. 3.
Set root to local node and
Move it to tentative list
Start
Is tentative
list empty
Among the nodes in the tentative
list, move the one with the
shortest path to permanent list
Add each unprocessed neighbor of last moved node into tentative list
(if the node is not in the list)
If neighbor is in tentative list with larger cumulative cost, replace it
with the new neighbor node
Stop NO
YES
Fig. 3. Dijkstra’s Algorithm

42. OSPF – Dijkstra’s Algorithm
Working example of Dijkstra’s Algorithm A B 5 D 3 E 4 C 2

43. OSPF – Dijkstra’s Algorithm
Move B to permanent list
Working Diagram
Set A as root and move A to tentative list A B 5 B 5
Node
Cost
Next Router A - B 5 C 2 D 3 E 6 C 2 D 3
Move C to permanent list and add node E to tentative list
Move A to permanent list and add node B, C, D to tentative list C 2 E 6
Move D to permanent list D 3 E 6
Move E to permanent list and tentative list is empty. Process Stop

44. Learn how to see the above processes using ospfd, and ospf6d.

45. Example: OSPF Interface Information
This command shows the interface configuration parameter such as costs, priority, DR/BDR for this interface, and Status.

46. Example: Neighbours
This command shows all neighbors connected to the node and their status.

47. Example: Link State Database
The type of LSA can be specify from the command and these is the 8 types of the LSA packet.

48. Example: Link State Database (cont)
This is the LSA database summary.

49. Example: Link State Information

50. Example: Shortest Path Tree
This is the SPF Tree information. The SPF tree is used to calculate the shortest path from each node to all other nodes in the area.

51. OSPF6D - Troubleshooting

52. Case 1 : Unable telnet to OSPF
Where is ospf6d process?
The telnet to OSPF failed because the process
of OSPF6D was not running

53. Case 1 : Successfully Telnet to OSPF
The telnet to OSPF success because
the process of OSPF6D was running
ospf6d process

54. Case 2: Unable to enter Full State with DR in OSPF
Changing the rl0 MTU size to
be 1500 bytes for OSPF6D

55. Case 2: Unable to enter Full State with DR in OSPF
Adjacency always stay at ExStart State
and will never proceed to Full State

56. Case 2: Unable to enter Full State with DR in OSPF
From the ospf6d.log file,
we can see that the
adjacency with DR was
stuck at Exstart State

57. Case 2: Successfully to enter Full State with DR
Changing the rl0 MTU size to
be 1452 bytes for OSPF6D

58. Case 2: Successfully to enter Full State with DR
From the ospf6d.log
we can see that now
the adjacency between
this router and DR can
proceed till Full State

59. Case 2: Successfully to enter Full State with DR
Now it can proceed till Full State

60. Case 3 : Router 172.16.51.3 DOWN The 172.16.51.3 doesn’t send
Hello packet, the router Dead
Timer was counting down.
Router Dead Timer for
was times up.
This router was wiped out
from neighbors list

61. Case 4 : Router 172.16.51.3 UP The 172.16.51.3 send
Hello packet, and received by
this router. Adjacency between
this 2 router running again.
Due to the parameter configuration
of this 2 router, both don’t want
to be DR/BDR, thus they stay at
Twoway/DRother state

62. Thank you