Unicast Routing in IPv6 Babu Ram Dawadi.

Unicast Routing in IPv6Unicast Routing in IPv6

Babu Ram DawadiBabu Ram Dawadi

IndexIndexa) What is a unicast routing protocol?

b) Discuss about RIPngc) What are the Routing Table Entries of RIPngd) Explain RIPng Message Format e) What are different timers of RIPngf) What is OSPF?g) How do OSPF routers on the same link establish

adjacencies? What does it mean to be adjacent? GWE.

h) How do OSPF routers synchronize their Link State Databases? GWE.

i) How to calculate the best route in OSPF? GWE.j) Learn how to see the above processes using ospfd,

and ospf6d.

Unicast Routing ProtocolUnicast Routing Protocol Unicast routing is a process that enable sender to send an unicast IP Unicast routing is a process that enable sender to send an unicast IP

packets to the destination node.packets to the destination node.

1 router or more intermediate routers may be used, depending to the 1 router or more intermediate routers may be used, depending to the destination of the node. (Figure 1)destination of the node. (Figure 1)

Unicast routing protocol is a set of rules of forwarding unicast traffic from Unicast routing protocol is a set of rules of forwarding unicast traffic from a source to a destination on an internetwork. a source to a destination on an internetwork.

`

Source (S)

`

Destination (D)

S D S D

SD

S D S D

Fig. 1. Unicast RoutingFig. 1. Unicast Routing

The router is using only The router is using only 1 port to forwards the 1 port to forwards the

received unicast packetreceived unicast packet

Unicast Routing ProtocolUnicast Routing Protocol Unicast Routing Protocol consists of:Unicast Routing Protocol consists of:

– RIP (Routing Information Protocol)– OSPF (– BGP

They each serve a different purpose.They each serve a different purpose.

RoutingRouting

InteriorInterior ExteriorExterior

RIPRIP OSPFOSPF BGPBGPFig. 2. Types of Unicast Routing ProtocolFig. 2. Types of Unicast Routing Protocol

RIPng (RFC 2080)RIPng (RFC 2080)

Based on Distance Vector algorithm known as Based on Distance Vector algorithm known as bellman ford algorithmbellman ford algorithm

Router keeps the following entries in the routing tableRouter 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

RIPng routing tableRIPng routing table

TimerTimer– Amount of time since the information about the route

was last updated

Route change flagRoute change flag– Set to control triggered routing updates

Route SourceRoute Source– Entity to provide route information eg: Ripng, OSPF etc..

RIPng Message FormatRIPng Message Format

UDP based protocol using udp port number 521UDP based protocol using udp port number 521

IPv6 Header

UDP Header

RIPng Header

RTE1 RTE2 RTE3 ……… RTEn

1: Request2: Response

20 Bytes/RTE

Command 1: ask system to send all Command 1: ask system to send all or part of its routing tableor part of its routing table

Command 2: sends an update Command 2: sends an update message containing all or parts of message containing all or parts of the senders routing table.the senders routing table.

Command 1B

Version 1B

Unused 2B

Routing Table Entry (RTE)Routing Table Entry (RTE)

RIPng header is followed by one or more routing RIPng header is followed by one or more routing table entries (format of Routing table entry)table entries (format of Routing table entry)

….16 B IPv6 Prefix

2 B Route Tag

1 B Prefix Length

1 B Metric(1-16)

RTE..RTE..

Route TagRoute 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]

TimersTimers– 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

TimerTimer

Timeout TimerTimeout 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)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.

OSPFOSPF The difference between intra-domain and inter-domain (Fig. 2.)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 protocolOSPF is an interior routing protocol– Intra-domain routing protocol

a) Intra-domaina) Intra-domain

Fig. 3. Interior Routing ProtocolFig. 3. Interior Routing Protocol

Router 1

Router 2

AS 1 AS 2

b) Inter-domainb) Inter-domain

OSPF HeaderOSPF Header

IPv6 Header NH: 89

OSPF Header OSPF Message

Version 1B

16 Byte

Instance ID 1BPacket

Length 2B

40Byte

RouterID 4B

AreaID 4B

Checksum 2B

Unused 1B

Packet Type 1B

OSPF ProcessOSPF Process Link State routingLink 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 Link State Database (LSDB) contains link state advertisement is send to every router in the same domain.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 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 A routing table can be derived from the SPF tree which contains the best route to each router. best route to each router.

Types of OSPF PacketsTypes of OSPF PacketsOSPF PacketsOSPF Packets

HELLOHELLO Database Database DescriptionDescription

Link StateLink StateRequestRequest

Link StateLink StateUpdateUpdate

Link StateLink StateAcknowledgementAcknowledgement

Router LinkRouter Link0x20010x2001

Network LinkNetwork Link0x20020x2002

Inter-Area-PrefixInter-Area-PrefixLSALSA

0x20030x2003

Inter-Area-RouterInter-Area-RouterLSALSA

0x20040x2004AS-External-LSAAS-External-LSA

0x40050x4005

Type 1Type 1 Type 2Type 2 Type 3Type 3 Type 4Type 4 Type 5Type 5

Group-Group-Membership-LSAMembership-LSA

0x20060x2006

Type-7-LSAType-7-LSA0x20070x2007

Link-LSALink-LSA0x00080x0008

Intra-Area-PrefixIntra-Area-PrefixLSALSA

0x20030x2003

Fig. 4. Types of OSPF PacketFig. 4. Types of OSPF Packet

How do OSPF routers on the same How do OSPF routers on the same link establish adjacencies? link establish adjacencies?

What does it mean to be What does it mean to be adjacent? GWE.adjacent? GWE.

OSPF- Forming AdjacenciesOSPF- Forming Adjacencies OSPF routers on the same link establish adjacenciesOSPF routers on the same link establish adjacencies

– Using Hello packet

An OSPF router need to go through 7 steps from no connection to An OSPF router need to go through 7 steps from no connection to full adjacency when it is first initialized.full adjacency when it is first initialized.– Down State– Init State– Two Way state– Exstart– Exchange State– Loading State– Full Adjacency

OSPF- Forming Adjacencies OSPF- Forming Adjacencies (cont)(cont)

Down State No information has yet been exchanged.

NoneNone

Init State Hello PacketHello Packet(Type 1)(Type 1)

Routers send hello packets at regular intervals to establish relationships.

Two-way State

Hello PacketHello Packet(Type 1)(Type 1)

A router sees itself in a hello packet.

ExstartHello PacketHello Packet

(Type 1)(Type 1)Routers negotiate master/slave relationship by comparing their router id using hello packets.

Exchange State

Database DescriptionDatabase Description(Type 2)(Type 2)

Neighbors start communicating their link-state information with the others.

Loading State

Link State RequestLink State RequestLink State UpdateLink State Update

Link State AcknowledgementLink State Acknowledgement(Type 3,4,5)(Type 3,4,5)

The router has the initial information of each route, they may request for more complete information.

Full AllAll(Type 1,2,3,4,5)(Type 1,2,3,4,5)Routers are fully adjacent.


Processing of Processing of Hello packetHello packet

Hello Packets from router neighbour XAuthentication

AreaID(Accepted)

Hello Interval match?

RouterDead Interval Match?

E- and N- bit match

Discard packet

Discard packet

Discard packet

Am I already adjacent to X?

Neighbour X sees me as neighbour?

Neighbour X changes to the 2-

way state

Incoming interface of type?

Is nieghbour X or am I DR/BDR

Neighbour X stays 2 ways

Forming Adjacency with Router X

NO

YES

YES

YES

NO

NO

NOYES

YES

YES

YES

Point to Point

Transit

NO

Reset timer of Neighbour X

NO

Neighbour X changes to the

INIT StateNO

Fig. 5. Processing a Hello PacketFig. 5. Processing a Hello Packet

(Reference: IPv6 Essential Pg.169)(Reference: IPv6 Essential Pg.169)


Forming an adjacencyForming an adjacency– Phases– Packet type involved

Router 2 (R2)Router 1(R1)

Point to Point (No DR,BDR)Transit Link (DR,BDR, or DROther)

Hello (Neighbour = 0)

Hello (Neighbour = R1)


DD (Seq = x, Init, More, Master)

DD (Seq = y, Init, More, Master)

DD (Seq = y, More, Slave)

DD (Seq = y+1, More, Master)

DD (Seq = y+1, More, Slave)

DD (Seq = y+n-1, More, Master) no more to send

DD (Seq = y+n-1, More, Slave)

DD (Seq = y+n, More, Master)

DD (Seq = y+n, More, Slave) no more to send

Link State Request

Link State Update

Link State Acknowledgement

Link State Request

Link State Update


Hello

Init2-Way

2-Way

Ex-StartEx-Start

Exchange Exchange

LoadingLoading

Full Full

TimTimee

The first OSPF neighbor is The first OSPF neighbor is DownDown state. It means that no state. It means that no information (hellos) has been information (hellos) has been received from this neighbor. received from this neighbor.

But it still can send Hello But it still can send Hello message to its neighboursmessage to its neighbours

Router 2 has received a Router 2 has received a hello packet from its hello packet from its

neighbor, but the neighbor, but the receiving router's ID receiving router's ID

was not included in the was not included in the hello packet hello packet

Router1 has seen the Router Router1 has seen the Router 2’s hello packet which had 2’s hello packet which had included its own Router ID included its own Router ID within the received hello within the received hello packet's neighbor field packet's neighbor field

Router2 also has received Router2 also has received the Router 1’s hello packet the Router 1’s hello packet which had also included its which had also included its

own Router ID within the own Router ID within the received hello packet's received hello packet's

neighbor fieldneighbor field

At this state, a router decides whether to At this state, a router decides whether to become adjacent with this neighbor. become adjacent with this neighbor.

The decision on adjacencies is always The decision on adjacencies is always depend on the link media. (Types of depend on the link media. (Types of network)network)

Point to PointPoint to Point-No DR/BDR is needed or used because No DR/BDR is needed or used because because only 2 neighbour routers.because only 2 neighbour routers.

Broadcast Multiple AccessBroadcast Multiple Access-DR and BDR are elected.-DR and BDR are elected.

Non-Broadcast Multiple AccessNon-Broadcast Multiple Access-DR and BDR are elected-DR and BDR are elected To Be

To Be

Continue...

Continue...

Fig. 6. Forming an Adjacencies – Part IFig. 6. Forming an Adjacencies – Part I



Types of Network:Types of Network:

Frame Relay

Broadcast Multiple Access

Ethernet, Token Ring

Point to Point

PPP, HDLC Non Broadcast Multiple Access (NBMA)

X.25, Frame RelayFig. 7. Types of NetworkFig. 7. Types of Network


When DR and BDR are elected, we can say that the adjacencies was When DR and BDR are elected, we can say that the adjacencies was established.established.

The DR and BDR are elected based on several criteriaThe 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 After adjacent, the routers already created reliable channels to their neighbors.neighbors.

These reliable channels is important for the routers to exchange Link These reliable channels is important for the routers to exchange Link State Database (LSDB) with the neighbors..State Database (LSDB) with the neighbors..

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

OSPF - OSPF - Link State DatabasesLink State Databases When the routers have elected DR When the routers have elected DR

and BDR, the databases need to and BDR, the databases need to get synchronized 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.

Router 2 (R2)Router 1(R1)

Point to Point (No DR,BDR)Transit Link (DR,BDR, or DROther)

Hello (Neighbour = 0)



DD (Seq = x, Init, More, Master)

DD (Seq = y, Init, More, Master)

DD (Seq = y, More, Slave)

DD (Seq = y+1, More, Master)

DD (Seq = y+1, More, Slave)

DD (Seq = y+n-1, More, Master) no more to send

DD (Seq = y+n-1, More, Slave)

DD (Seq = y+n, More, Master)

DD (Seq = y+n, More, Slave) no more to send

Link State Request

Link State Update


Link State Request

Link State Update


Hello

Init2-Way

2-Way

Ex-StartEx-Start

Exchange Exchange

LoadingLoading

Full Full

The Router 1 is The Router 1 is attempted to start the attempted to start the

Exchange because Exchange because “he” might thought “he” might thought

that “he” has the that “he” has the highest Router ID highest Router ID

But Router 2 will But Router 2 will reply “No”. I will reply “No”. I will

start the Exchange start the Exchange State first, because State first, because

I have a higher I have a higher Router IDRouter ID

!!But your DR/BDRBut your DR/BDR election might be purelyelection might be purely

based on the based on the higher priority higher priority

configure configure on routeron router

!!It might logic to concludeIt might logic to conclude that the DR/BDR with the that the DR/BDR with the

highest Router ID will become highest Router ID will become the master during this process of the master during this process of

master/slave election.master/slave election.

After the election of Master After the election of Master and Slave, the routers start and Slave, the routers start

exchange database exchange database descriptor (DBD) packets. descriptor (DBD) packets.

DBD contain link-DBD contain link-state advertisement state advertisement (LSA) headers only (LSA) headers only

and describe the and describe the contents of the contents of the entire link-state entire link-state

database database

Each DBD packet has a Each DBD packet has a sequence number sequence number

which can be which can be incremented only by incremented only by master and explicitly master and explicitly

acknowledged by slave acknowledged by slave

In this state, the In this state, the actual exchange of actual exchange of link state information link state information occurs occurs

Based on the Based on the information information provided by the provided by the DBDs, routers DBDs, routers send link-state send link-state request packets request packets

The neighbor The neighbor then provides the then provides the requested link-requested link-state information state information in link-state in link-state update packets update packets

Routers are fully Routers are fully adjacent with each adjacent with each other. All the router and other. All the router and network LSAs are network LSAs are exchanged and the exchanged and the routers' databases are routers' databases are fully synchronized. fully synchronized.

Fig. 7. Forming an Adjacencies-Part IIFig. 7. Forming an Adjacencies-Part II


OSPF – Database Description (DBD) PacketOSPF – Database Description (DBD) Packet

OSPF Packet Type 2OSPF Packet Type 2Database Description PacketDatabase Description Packet

Database Description fields:Database Description fields:I bit = Init bitI bit = Init bit

M bit = More bitM bit = More bitMS bit = Master / Slave bitMS bit = Master / Slave bit


I bitI bit is set to is set to11Indicate that this is First DBD packet send by this router 172.16.51.3Indicate that this is First DBD packet send by this router 172.16.51.3

This packet contain no data.This packet contain no data.

M bitM bit is set to is set to 11Indicate that there are more DBD packets to followIndicate that there are more DBD packets to follow

MS bitMS bit is set to is set to 11Indicate that this router (172.16.51.3) declares itself to be MasterIndicate that this router (172.16.51.3) declares itself to be Master


I bitI bit is set to is set to 11Indicate that this is First DBD packet send by this router 202.249.25.234Indicate that this is First DBD packet send by this router 202.249.25.234

This packet contain no data.This packet contain no data.

M bitM bit is set to is set to 11Indicate that there are more DBD packets to followIndicate that there are more DBD packets to follow

MS bitMS bit is set to is set to 11Indicate that this router (202.249.25.234) declares itself to be MasterIndicate that this router (202.249.25.234) declares itself to be Master

EmptyEmpty


I bitI bit is set to is set to 00Indicate that this is NOT First DBD packet send by this router 172.16.51.3.Indicate that this is NOT First DBD packet send by this router 172.16.51.3.

It contain database description of router 172.16.51.3It contain database description of router 172.16.51.3

M bitM bit is set to is set to 00Indicate that there are no more DBD packets to sendIndicate that there are no more DBD packets to send

All database descriptions have been sent All database descriptions have been sent

MS bitMS bit is set to is set to 00Indicate that this router (172.16.51.3) declares itself to be SlaveIndicate that this router (172.16.51.3) declares itself to be Slave


I bitI bit is set to is set to 00Indicate that this is NOT First DBD packet send by this router 202.249.25.234Indicate that this is NOT First DBD packet send by this router 202.249.25.234


M bitM bit is set to is set to 11Indicate that there are more DBD packets to sendIndicate that there are more DBD packets to send

The database descriptions will still be sent The database descriptions will still be sent

MS bitMS bit is set to is set to 11Indicate that this router (202.249.25.234) is still a MasterIndicate that this router (202.249.25.234) is still a Master


I bitI bit is set to is set to 00Indicate that this is NOT First DBD packet send by this router 172.16.51.3.Indicate that this is NOT First DBD packet send by this router 172.16.51.3.




MS bitMS bit is set to is set to 00Indicate that this router (172.16.51.3) is still a SlaveIndicate that this router (172.16.51.3) is still a Slave

EmptyEmpty

The router 172.16.51.3 is still sendingThe router 172.16.51.3 is still sending a empty packet even it had no dataa empty packet even it had no data

description to send. This empty packetdescription to send. This empty packetis help to keep the DBD sequence number is help to keep the DBD sequence number matched because router 202.249.25.234 matched because router 202.249.25.234

is still sending the DBD packet.is still sending the DBD packet.


I bitI bit is set to is set to 00Indicate that this is NOT First DBD packet send by this router 202.249.25.234Indicate that this is NOT First DBD packet send by this router 202.249.25.234



All database descriptions have been sentAll database descriptions have been sent

MS bitMS bit is set to is set to 11Indicate that this router (202.249.25.234) is still a MasterIndicate that this router (202.249.25.234) is still a Master


I bitI bit is set is set 00Indicate that this is NOT First DBD packet send by this router 172.16.51.3.Indicate that this is NOT First DBD packet send by this router 172.16.51.3.

M bitM bit is set is set 00Indicate that there are no more DBD packets to sendIndicate that there are no more DBD packets to send


MS bitMS bit is set is set 00Indicate that this router (172.16.51.3) is still a SlaveIndicate that this router (172.16.51.3) is still a Slave

EmptyEmpty

Now, both router has nothing more to send

Now, both router has nothing more to send

All the router now enter to the

All the router now enter to the

Loading State

Loading State

OSPF – Link State Request PacketOSPF – Link State Request Packet

OSPF Packet Type 2OSPF Packet Type 2Link State Request PacketLink State Request Packet

Multiple requests can be sentMultiple requests can be sentusing a single packet.using a single packet.

(Reference IPv6 Essential pg.172)(Reference IPv6 Essential pg.172)

OSPF – Link State Update Packet (0x2001)OSPF – Link State Update Packet (0x2001)


Link State Update Packet Type 0x2001Link State Update Packet Type 0x2001Router-LSARouter-LSA



Link State Update Packet Type 0x2002Link State Update Packet Type 0x2002Network-LSANetwork-LSA



Link State Update Packet Type 0x4005Link State Update Packet Type 0x4005AS-External-LSAAS-External-LSA



Link State Update Packet Type 0x0008Link State Update Packet Type 0x0008Link-LSALink-LSA

Purpose: List all IPv6 Prefix attached to the linkPurpose: List all IPv6 Prefix attached to the link



Link State Update Packet Type 0x2009Link State Update Packet Type 0x2009Intra-Prefix-LSAIntra-Prefix-LSA

Each Link Update Request must be

Each Link Update Request must be

Acknowledged by

Acknowledged by

Link State Acknowledgment Packet

Link State Acknowledgment Packet

OSPF – Link State Acknowledgement PacketOSPF – Link State Acknowledgement Packet

OSPF Packet Type 5OSPF Packet Type 5Link State Acknowledgement PacketLink State Acknowledgement Packet

All the router now enter the

All the router now enter the

Full State Full State

Hello packet is still sending

Hello packet is still sending

to keep the adjacency alive

to keep the adjacency alive

Learn how to see the above Learn how to see the above processes using ospfd, and processes using ospfd, and

ospf6d.ospf6d.

Example: OSPF Interface InformationExample: OSPF Interface Information

This command shows the interface configuration parameter such as costs, priority, DR/BDR for this interface, and Status.

Example: NeighboursExample: Neighbours

This command shows all neighbors connected to the node and their status.

Example: Link State DatabaseExample: Link State Database

The type of LSA can be specify from the command and these is the 8 types of the LSA packet.

Example: Link State Database Example: Link State Database (cont)(cont)

This is the LSA database summary.

Example: Link State InformationExample: Link State Information

Example: Shortest Path TreeExample: 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.

OSPF6D - TroubleshootingOSPF6D - Troubleshooting

Case 1 : Unable telnet to OSPFCase 1 : Unable telnet to OSPF

Where is ospf6d process?

The telnet to OSPF failed because the process of OSPF6D was not running

Case 1 : Successfully Telnet to OSPFCase 1 : Successfully Telnet to OSPF

The telnet to OSPF success because the process of OSPF6D was running

ospf6d process

Case 2: Unable to enter Full State with DR in OSPFCase 2: Unable to enter Full State with DR in OSPF

Changing the rl0 MTU size tobe 1500 bytes for OSPF6D


Adjacency always stay at ExStart Stateand will never proceed to Full State


From the ospf6d.log file,we can see that the

adjacency with DR was stuck at Exstart State

Case 2: Successfully to enter Full State with DRCase 2: Successfully to enter Full State with DR

Changing the rl0 MTU size tobe 1452 bytes for OSPF6D


From the ospf6d.logwe can see that now

the adjacency between this router and DR can proceed till Full State


Now it can proceed till Full State

Case 3 : Router 172.16.51.3 DOWNCase 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 172.16.51.3 was times up.This router was wiped out

from neighbors list

Case 4 : Router 172.16.51.3 UPCase 4 : Router 172.16.51.3 UP

The 172.16.51.3 send Hello packet, and received bythis router. Adjacency between

this 2 router running again.

Due to the parameter configurationof this 2 router, both don’t wantto be DR/BDR, thus they stay at

Twoway/DRother state

Thank youThank you

Unicast Routing in IPv6 Babu Ram Dawadi.

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Transcript of Unicast Routing in IPv6 Babu Ram Dawadi.