ospfv3 primer

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OSPFv3 Differences with IPv2

IntroductionIf you plan to use OSPF for IPv6 in a dual stack network you will run two protocols: OSPFv2 for IPv4 and OSPFv3 for IPv6. If you want an integrated routing protocol which will manage both routing tables, use IS-IS.

Differences with IPv4In IPv6, an interface may have many IP addresses. Thus OSPFv3 runs per link and not per subnet.In OSPFv3, the Option field in Hello and Database Description have been expanded to 24 bits.The Hello packet does not contain any address but an Interface-id.There are two new bits: the R-bit and the V6-bit. If the R-bit is set the router participate will forward traffic. The options bit ‘R-bit” and “V6-bit’ have been added. If the R-bit is cleared, the router is not used for forwarding transit traffic. To forward IPv6 traffic, the V6-bit must be set.The OSPF packet header now includes an “Instance ID” that allows multiple independent instance of OSPF to run on the same protocol.

Option bitsDC R N x E V6OSPFv2 and OSPFv3 are running as Ships in the night

• OSPFv2 and OSPFv3 are running as Ships in the night

• Authentication has been Removed

• OSPFv3 run per link and not per subnet

• It is now possible to run multiple instances of OSPF on the same media

• The Option bits have been expanded to 24 bits. Two new bit “R-bit’, “V6-bits. If the R-bit is clear, the router does not forward traffic. To forward IPv6 Traffic IPv6-bit must be set.

• Permit to run 256 instances on the same shared media.

•• Security is managed by IPSec and is

no longer part of OSPF Process.

• As many addresses can be configured on each link, OSPFv3 run per link and not per subnet.

• OSPF Database has been redesigned with 2 new LSAs. One LSA to

http://www.ipv6forlife.com

OPSFv3 is a new Routing Protocol independent from OSPFv2 for IPv4.


http://tools.ietf.org/html/rfc5340#appendix-A.2



LengthLink State ChecksumLink State Sequence NumberAdvertising RouterLink State IDLS TypeLS age

OSPFv3 http://www.ipv6forlife.com

Area did not changeWe still have regular, area, stub, or NSSA Areas.

Please note that if Authentication has been removed it is that it is assumed that all nodes run IPSec.

www.ipv6forlife.com

In IPv6, an interface may have many IP addresses. Thus OSPFv3 runs per link and not per subnet.In OSPFv3, the Option field in Hello and Database Description has been expanded to 24 bits.The Hello packet does not contain any address but an Interface-id.There are two new bits: the R-bit and the V6-bit. If the R-bit is set the router participate will forward traffic. The options bit ‘R-bit” and “V6-bit’ have been added. If the R-bit is cleared, the router is not used for forwarding transit traffic. To forward IPv6 traffic, the V6-bit must be set.The OSPF packet header now includes an “Instance ID” that allows multiple independent instances of OSPF to run on the same protocol.

Option bitsDC R N x E V6OSPFv2 and OSPFv3 are running as Ships in the night Permit to run 256 instances on the same shared media.

HELLO PROTOCOL

With OSPF exchanges start with Hello and all OSPF packets starts with a common headers.They are 5 types of packets in OSPF.

Two routers are sending Hellos using the AllOspfRouters Multicast address ff02::5.

The Finite State Machine for the interface goes:DOWN -> INIT

During the INIT state they check that the parameters found in Hello are compatible. For instance if they are not in the same Area or do both not send hello every 10 seconds, they will not form Neighbour relationship.

When a router sees its Router-ID in a Neighbour advertisement, their states becomes TWO-WAY

OSPFv3 run per link and not per SubnetAs many addresses can be configured on the same interface, OSPF run per link and not per Subnet.

Still the same Architectiure







HELLO Messages

No 1

Page � - OSPFv34

DR/BDR Election. In addition, they will elect a Designated Router and a Backup Designated Router on Multipoint, Broadcast or Not, interface. They start waiting 40 seconds listening if there are already a DR/BDR on this link. Then they compare their Router Priority with the Priority of the others received. This is not preemptive, if a DR is elected you would not replace it either should you have a better priority. With the same priority, highest Router ID wins. Priority 0 is ineligible.

The next state is Database synchronisation with Adjacent routers. On a Point-to-Point you should be systematically adjacent. On a multiaccess you only become adjacent with the DR/BDR. This is to avoid that everybody need to synchronise with everybody!

It is important to notice that there is no MTU check during these steps, it will be verified next. In IS-IS Hellos are sent at MTU to check that they can support the same length.

OSPF Initialisation (To be Continued) No need for DR/BDR on a Point-to-Point

EXSTART Once, routers are neighbours, they may become adjacent.Each router send a DBD with the Master bit set (MS) pretending it is the Master. Highest Router-ID wins.

DBD other bits are: I-bit The Init bit. When set to 1, this packet is the first in the sequence of Database Description packets.

M-bit The More bit. When set to 1, it indicates that more Database Description packets are to follow.

MS-bit The Master/Slave bit. When set to 1, it indicates that the router is the master during the Database Exchange process. Otherwise, the router is the slave.The Master will then be responsible to synchronise the communication. This exchange looks like a TFTP File Transfer. Each router sends its database, JSA Headers only to heck it has the latest version.

During the DBD Exchange the Routers are in the EXCHANGE State.

EXLOADIf a LSA is not up to date, the router will send a Link State Request. It's neighbour should now reply with a Link-State Reply which will be Acked with a Link State Acknowledgement. When both Databases are up to date, the status is now FULL.

Packet Length3 2

Router-ID

Area-ID

Checksum Instance ID 0

Database Description Packet

0 Options

Interface MTU 0 0 0 0 0 0 I M MS

DD Sequence Number

An LSA Header

Packet Length3 3

Router-ID

Area-ID


Link State Request

0 LS Type

Link-State ID

Advertising Router

Link-State ID....

Packet Length3 4

Router-ID

Area-ID


Link State Update

# Link State

LSAs....

Packet Length3 5

Router-ID

Area-ID


Link State Acknowledgement

An LSA Header

LS Age LS Type

Link State ID

Advertising Router

LS Sequence Number

LS Checksum Length

LSA Header

LSA Type

U S2 S1 LSA Function CodeU=0 Treat the LSA as if it had link-local flooding scopeU=1 Store and Flood the LSA as if the type is understood

S2 S1 Flooding Scope0 0 Link-Local Scoping0 1 Area Scoping1 0 AS Scoping1 1 Reserved

LSA Function Code LS-Type1 0x2001 Router-LSA2 0x2002 Network-LSA3 0x2003 Inter-Area-Prefix-LSA4 0x2004 Inter-Area_Router-LSA5 0x2005 AS-External-LSA6 Deprecated7 0x2007 NSSA-LSA9 0x2009 Intra-Area-Prefix-LSA

RID 10.0.0.1 RID 10.0.0.2

10.0.0.1 DBD I, M, MS==1

10.0.0.2I. M, MS=1

10.0.0.1DBD

EXSTART

10.0.0.2 > 10.0.0.1 so 10.0.0.2 becomes the mater

EXCHANGE

10.0.0.2DBD Seq=X

10.0.0.1DBD Ack X

If a LSA is missing or not up to date, then request it10.0.0.1LS Req

10.0.0.2LS Upd

10.0.01!LS Ack

EXLOAD

EXFULL

10.0.0.2DBD MS=1, M=0

OSPF Initialisation on (Continued)

On

With OSPF, we see the networks in different categories.

Point-to-point or Multipoint. The Multipoint uses a DR/BDR to optimise the Exchanges and to generate a single LSA on the behalf of all neighbours instead having each node generating an LSA to list all neighbours on the multi access networks.

The GigabitEthernet are configured by default are broadcast for OSPF which is bad for Point-to-Point Link.We are going to go through the DR /BDR Election, start waiting 40 seconds just listening for an existing active DR. If we configure the interface as point-to-point, it will go faster as it will not wait and start the DBD Exchange faster.

On a CISCO Router we can see that ll OSPFv3 Gigabit Interface are BROADCAST by default which is no good for convergence. When the interface goes up it wait 40 seconds just listening the network.You can change the network type with the command “ip ospf network-type poit-to-point”.

R2>sh ipv6 ospf ne

Neighbor ID Pri State Dead Time Interface ID Interface 10.0.0.4 1 FULL/DROTHER 00:00:39 5 GigabitEthernet0/0 10.0.0.3 1 FULL/BDR 00:00:32 6 GigabitEthernet0/0 10.0.0.3 1 FULL/BDR 00:00:31 5 GigabitEthernet2/0 10.0.0.5 1 FULL/BDR 00:00:33 6 GigabitEthernet1/0

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Different types of OSPF Networks

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Case Study of a Network: R5, R2 area in AREA 0. R2 is an ABR and connect R3 in Stub AREA 2.R4 is an ABR and connect R6 in AREA 1. R6 is an ASBR.

Database of an ASBR R6.

R6#sh ipv6 ospf data

OSPFv3 Router with ID (10.0.0.6) (Process ID 1)

Router Link States (Area 1)

ADV Router Age Seq# Fragment ID Link count Bits 10.0.0.4 301 0x80000003 0 1 B 10.0.0.6 587 0x80000005 0 1 E

Net Link States (Area 1)

ADV Router Age Seq# Link ID Rtr count 10.0.0.6 192 0x80000002 5 2 Inter Area Prefix Link States (Area 1)

ADV Router Age Seq# Prefix 10.0.0.4 301 0x80000002 2001:DB8::2/128 10.0.0.4 301 0x80000002 2001:DB8::3/128 10.0.0.4 301 0x80000002 2001:DB8:1::/64 10.0.0.4 1512 0x80000001 2001:DB8:1000::/64

Link (Type-8) Link States (Area 1) ADV Router Age Seq# Link ID Interface 10.0.0.4 307 0x80000002 8 Gi0/0 10.0.0.6 473 0x80000002 5 Gi0/0

Intra Area Prefix Link States (Area 1)

ADV Router Age Seq# Link ID Ref-lstype Ref-LSID 10.0.0.6 227 0x80000002 5120 0x2002 5

Type-5 AS External Link States

ADV Router Age Seq# Prefix 10.0.0.6 629 0x80000001 2001:DB8:AAA1::/48 10.0.0.6 629 0x80000001 2001:DB8:AAA2::/48 10.0.0.6 629 0x80000001 2001:DB8:AAAA::/48

Let’s take a closer look at another router, R2 and check its Router LSA. Router LSA Type 1:

R2>show ipv6 ospf database router adv 10.0.0.2



LS age: 781 Options: (V6-Bit, E-Bit, R-bit, DC-Bit) LS Type: Router Links Link State ID: 0 Advertising Router: 10.0.0.2 LS Seq Number: 80000011 Checksum: 0x492B Length: 72 Number of Links: 3

Link connected to: a Transit Network Link Metric: 1 Local Interface ID: 5 Neighbor (DR) Interface ID: 5 Neighbor (DR) Router ID: 10.0.0.2



And now addresses are advertised by the new Intra-Area-Prefix-LSA

R2>show ipv6 ospf database prefix adv 10.0.0.2



Routing Bit Set on this LSA LS age: 1919 LS Type: Intra-Area-Prefix-LSA Link State ID: 0 Advertising Router: 10.0.0.2 LS Seq Number: 80000003 Checksum: 0xA2D6 Length: 52 Referenced LSA Type: 2001 Referenced Link State ID: 0 Referenced Advertising Router: 10.0.0.2 Number of Prefixes: 1 Prefix Address: 2001:DB8::2 Prefix Length: 128, Options: LA, Metric: 0

Routing Bit Set on this LSA LS age: 910 LS Type: Intra-Area-Prefix-LSA Link State ID: 5120 Advertising Router: 10.0.0.2 LS Seq Number: 80000003 Checksum: 0xDDCC Length: 44 Referenced LSA Type: 2002 Referenced Link State ID: 5 Referenced Advertising Router: 10.0.0.2 Number of Prefixes: 1 Prefix Address: 2001:DB8:1:: Prefix Length: 64, Options: None, Metric: 0

Routing Bit Set on this LSA LS age: 925 LS Type: Intra-Area-Prefix-LSA Link State ID: 6144 Advertising Router: 10.0.0.2 LS Seq Number: 80000005 Checksum: 0xB7EB Length: 44 Referenced LSA Type: 2002 Referenced Link State ID: 6 Referenced Advertising Router: 10.0.0.2 Number of Prefixes: 1 Prefix Address: 2001:DB8:1:: Prefix Length: 64, Options: None, Metric: 0

On R4 the Inter-Area-Router LSA which has a new name. It is advertised by the ABR R4 to find the ASBR R6:

R2>show ipv6 ospf data inter-area router


Inter Area Router Link States (Area 0)

Routing Bit Set on this LSA LS age: 312 Options: (V6-Bit, E-Bit, R-bit, DC-Bit) LS Type: Inter Area Router Links Link State ID: 167772166 Advertising Router: 10.0.0.4 LS Seq Number: 80000003 Checksum: 0x6C69 Length: 32 Metric: 1 Destination Router ID: 10.0.0.6

R2>show ipv6 ospf data link


Link (Type-8) Link States (Area 0)

LS age: 1285 Options: (V6-Bit, E-Bit, R-bit, DC-Bit) LS Type: Link-LSA (Interface: GigabitEthernet0/0) Link State ID: 5 (Interface ID) Advertising Router: 10.0.0.2 LS Seq Number: 80000005 Checksum: 0xC57F Length: 44 Router Priority: 1 Link Local Address: FE80::C801:2FF:FE69:8 Number of Prefixes: 0

Let’s take a look at a Backbone router Database now:

R2>sh ipv6 ospf database



ADV Router Age Seq# Fragment ID Link count Bits 10.0.0.2 1202 0x80000016 0 3 None 10.0.0.3 1169 0x80000015 0 3 B 10.0.0.4 1813 0x80000018 0 2 B 10.0.0.5 294 0x80000012 0 3 None


ADV Router Age Seq# Link ID Rtr count 10.0.0.2 1202 0x80000009 5 3 10.0.0.2 1454 0x80000008 6 2 10.0.0.2 1712 0x80000008 7 2 10.0.0.3 1169 0x80000008 7 2 10.0.0.5 1047 0x80000008 5 2

Inter Area Prefix Link States (Area 0)

ADV Router Age Seq# Prefix 10.0.0.3 927 0x80000007 2001:DB8:1000::/64 10.0.0.4 1814 0x80000007 2001:DB8:2::/64

Inter Area Router Link States (Area 0)

ADV Router Age Seq# Link ID Dest RtrID 10.0.0.4 325 0x80000007 167772166 10.0.0.6


ADV Router Age Seq# Link ID Interface 10.0.0.2 1969 0x80000008 5 Gi0/0 10.0.0.3 1685 0x80000008 6 Gi0/0 10.0.0.4 1087 0x80000009 5 Gi0/0 10.0.0.2 1969 0x80000008 7 Gi2/0 10.0.0.3 1685 0x80000008 5 Gi2/0 10.0.0.2 707 0x80000009 6 Gi1/0 10.0.0.5 548 0x8000000C 6 Gi1/0


ADV Router Age Seq# Link ID Ref-lstype Ref-LSID 10.0.0.2 1969 0x80000008 0 0x2001 0 10.0.0.2 950 0x80000008 5120 0x2002 5 10.0.0.2 951 0x8000000A 6144 0x2002 6 10.0.0.3 1686 0x80000008 0 0x2001 0

Type-5 AS External Link States

ADV Router Age Seq# Prefix 10.0.0.6 158 0x80000007 2001:DB8:AAA1::/48 10.0.0.6 158 0x80000007 2001:DB8:AAA2::/48 10.0.0.6 158 0x80000007 2001:DB8:AAAA::/48

If we change the Network type to Point-to-Point for the Gigabit Interfaces, the Net Link State will disappear and the convergence will be optimized since there will be no DR/BDR Election. Let’s go!We can check on R2, only one network remains BROADCAST with 2 neighbors:

R2(config-if)#do sh ipv6 ospf neighbor

Neighbor ID Pri State Dead Time Interface ID Interface 10.0.0.4 1 FULL/DR 00:00:30 5 GigabitEthernet0/0 10.0.0.3 1 FULL/BDR 00:00:36 6 GigabitEthernet0/0 10.0.0.3 1 FULL/ - 00:00:36 5 GigabitEthernet2/0 10.0.0.5 1 FULL/ - 00:00:33 6 GigabitEthernet1/0

R2(config-if)#do show ipv6 ospf database



ADV Router Age Seq# Fragment ID Link count Bits 10.0.0.2 293 0x80000062 0 3 None 10.0.0.3 291 0x8000005B 0 3 B 10.0.0.4 294 0x80000043 0 2 B 10.0.0.5 530 0x8000001A 0 3 None


ADV Router Age Seq# Link ID Rtr count 10.0.0.4 299 0x80000002 5 3

Inter Area Prefix Link States (Area 0)

ADV Router Age Seq# Prefix 10.0.0.3 798 0x80000009 2001:DB8:1000::/64 10.0.0.4 1632 0x80000008 2001:DB8:2::/64

Inter Area Router Link States (Area 0) ADV Router Age Seq# Link ID Dest RtrID 10.0.0.4 150 0x80000008 167772166 10.0.0.6


ADV Router Age Seq# Link ID Interface 10.0.0.2 379 0x80000001 5 Gi0/0 10.0.0.3 342 0x80000001 6 Gi0/0 10.0.0.4 359 0x80000001 5 Gi0/0 10.0.0.2 514 0x8000000A 7 Gi2/0 10.0.0.3 717 0x8000000B 5 Gi2/0 10.0.0.2 525 0x8000000A 6 Gi1/0 10.0.0.5 673 0x8000000D 6 Gi1/0


ADV Router Age Seq# Link ID Ref-lstype Ref-LSID 10.0.0.2 530 0x8000000C 0 0x2001 0 10.0.0.3 808 0x8000000A 0 0x2001 0 10.0.0.4 319 0x80000001 5120 0x2002 5

Type-5 AS External Link States ADV Router Age Seq# Prefix 10.0.0.6 1978 0x80000007 2001:DB8:AAA1::/48 10.0.0.6 1979 0x80000007 2001:DB8:AAA2::/48 10.0.0.6 1979 0x80000007 2001:DB8:AAAA::/48

Exemple of new Prefix LSA that we had displayed before the change:

R2#show ipv6 ospf database router adv 10.0.0.2



LS age: 552 Options: (V6-Bit, E-Bit, R-bit, DC-Bit) LS Type: Router Links Link State ID: 0 Advertising Router: 10.0.0.2 LS Seq Number: 80000063 Checksum: 0x1709 Length: 72 Number of Links: 3


Link connected to: another Router (point-to-point) Link Metric: 1 Local Interface ID: 7 Neighbor Interface ID: 5 Neighbor Router ID: 10.0.0.3

Link connected to: another Router (point-to-point) Link Metric: 1 Local Interface ID: 6 Neighbor Interface ID: 6 Neighbor Router ID: 10.0.0.5

Before we changed the interface type to point to point it was:

R2>show ipv6 ospf database router adv 10.0.0.2



LS age: 781 Options: (V6-Bit, E-Bit, R-bit, DC-Bit) LS Type: Router Links Link State ID: 0 Advertising Router: 10.0.0.2 LS Seq Number: 80000011 Checksum: 0x492B Length: 72 Number of Links: 3




So changing to Point-to-point the Ethernet Interface not only save convergence but it also make the computation of the SPF simpler.

From R4

R4#sh bgp ipv6 u sum BGP router identifier 10.0.0.4, local AS number 65000 BGP table version is 1, main routing table version 1

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd FE80::C801:5FF:FEDC:8%GigabitEthernet0/0 4 100 0 0 0 0 0 never Active FE80::C801:5FF:FEDC:1C%GigabitEthernet0/0 4 100 0 0 0 0 0 never Active R4#

From R4 is seems that network is flipping:

R3> *Nov 4 20:32:30.919: %OSPFv3-5-ADJCHG: Process 1, Nbr 10.0.0.2 on GigabitEthernet0/0.1 from LOADING to FULL, Loading Donesh ipv os *Nov 4 20:32:34.783: %OSPFv3-5-ADJCHG: Process 1, Nbr 10.0.0.1 on GigabitEthernet0/0.1 from LOADING to FULL, Loading Donepf ne

Neighbor ID Pri State Dead Time Interface ID Interface 10.0.0.1 1 FULL/DROTHER 00:00:38 5 GigabitEthernet0/0.1 10.0.0.2 1 FULL/DR 00:00:35 5 GigabitEthernet0/0.1 R3> *Nov 4 20:32:40.183: %OSPFv3-5-ADJCHG: Process 1, Nbr 10.0.0.2 on GigabitEthernet0/0.1 from LOADING to FULL, Loading Done *Nov 4 20:32:40.191: %OSPFv3-5-ADJCHG: Process 1, Nbr 10.0.0.1 on GigabitEthernet0/0.1 from LOADING to FULL, Loading Done *Nov 4 20:32:49.751: %OSPFv3-4-ERRRCV: Received invalid packet: Bad Checksum from FE80::C801:5FF:FEDC:8, GigabitEthernet0/0.1 *Nov 4 20:32:54.499: %OSPFv3-5-ADJCHG: Process 1, Nbr 10.0.0.1 on GigabitEthernet0/0.1 from LOADING to FULL, Loading Done *Nov 4 20:32:54.691: %OSPFv3-5-ADJCHG: Process 1, Nbr 10.0.0.2 on GigabitEthernet0/0.1 from LOADING to FULL, Loading Done *Nov 4 20:32:59.371: %OSPFv3-4-ERRRCV: Received invalid packet: Bad Checksum from FE80::C801:5FF:FEDC:8, GigabitEthernet0/0.1 *Nov 4 20:32:59.439: %OSPFv3-5-ADJCHG: Process 1, Nbr 10.0.0.2 on GigabitEthernet0/0.1 from LOADING to FULL, Loading Done

This is a tricky situation when network is sometime working and sometime not! I hate this situation but i am hack buster of not ?

ospfv3 primer

Technology

ospf database

ipv6 trac

ospf packets

multiple instances of

ospf exchanges

ospf process

new bits

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