IGP: Open Shortest Path First v3

1
IGP Open Shortest Path First v3

• Dr. Dimitrios Kalogeras
• GRNET

2
IGP IS/IS

• Distance Vector IGPs
• RIP
• RIP2
• IGRP
• EIGRP
• Link State IGPs
• OSPF
• IS/IS

3
OSPFv2

• April 1998 was the most recent revision (RFC
  2328)
• OSPF uses a 2-level hierarchical model
• SPF calculation is performed independently for
  each area
• Typically faster convergence than DVRPs
• Relatively low, steady state bandwidth
  requirements

4
OSPFv3 overview

• OSPF for IPv6
• Based on OSPFv2, with enhancements
• Distributes IPv6 prefixes
• Runs directly over IPv6
• Ships-in-the-night with OSPFv2

5
OSPFv3 / OSPFv2 Similarities

• Basic packet types
• Hello, DBD, LSR, LSU, LSA
• Mechanisms for neighbor discovery and adjacency
  formation
• Interface types
• P2P, P2MP, Broadcast, NBMA, Virtual
• LSA flooding and aging
• Nearly identical LSA types

6
OSPFv3 / OSPFv2 Differences

• OSPFv3 runs over a link, rather than a subnet
• Multiple instances per link
• OSPFv2 topology not IPv6-specific
• Router ID
• Link ID
• Standard authentication mechanisms
• Uses link-local addresses
• Generalized flooding scope
• Two new LSA types

7
LSA Type Review
LSA Function Code
LSA type
Router-LSA
1
0x2001
2
0x2002
Network-LSA
Inter-Area-Prefix-LSA
3
0x2003
4
0x2004
Inter-Area-Router-LSA
0x4005
AS-External-LSA
5
Group-membership-LSA
6
0x2006
7
Type-7-LSA
0x2007
8
Link-LSA
0x0008
Intra-Area-Prefix-LSA
9
0x2009
8
Link LSA

• A link LSA per link
• Link local scope flooding on the link with which
  they are associated
• Provide router link local address
• List all IPv6 prefixes attached to the link
• Assert a collection of option bit for the
  Router-LSA

9
Inter-Area Prefix LSA

• Describes the destination outside the area but
  still in the AS
• Summary is created for one area, which is flooded
  out in all other areas
• Originated by an ABR
• Only intra-area routes are advertised into the
  backbone
• Link State ID simply serves to distinguish
  inter-area-prefix-LSAs originated by the same
  router
• Link-local addresses must never be advertised in
  inter-area- prefix-LSAs

10
Configuring OSPFv3 in Cisco IOS Software

• Similar to OSPFv2
• Prefixing existing Interface and Exec mode
  commands with ipv6
• Interfaces configured directly
• Replaces network command
• Native IPv6 router mode
• Not a sub-mode of router ospf

11
Configuration Modes in OSPFv3

• Entering router mode
• no ipv6 router ospf ltprocess IDgt
• Entering interface mode
• no ipv6 ospf ltprocess IDgt area ltarea IDgt
• Exec mode
• no show ipv6 ospf ltprocess IDgt
• clear ipv6 ospf ltprocess IDgt

12
Cisco IOS OSPFv3 Specific Attributes

• Configuring area range
• no area ltarea IDgt range ltprefixgt/ltprefix
  lengthgt
• Showing new LSA
• show ipv6 ospf ltprocess IDgt database link
• show ipv6 ospf ltprocess IDgt database prefix

13
OSPFv3 Debug Commands

• Adjacency is not appearing
• no debug ipv6 ospf adj
• no debug ipv6 ospf hello
• SPF is running constantly
• no debug ipv6 ospf spf
• no debug ipv6 ospf flooding
• no debug ipv6 ospf events
• no debug ipv6 ospf lsa-generation
• no debug ipv6 ospf database-timer
• General purpose
• no debug ipv6 ospf packets
• no debug ipv6 ospf retransmission
• no debug ipv6 ospf tree

14
OSPFv3 configuration example
Area 0
Router2
LAN1 2001111/64
Eth0
Router1
Eth1
LAN2 2001222/64
Area 1
15
Cisco IOS OSPFv3 Display
Area 0
Router2
Area 1
16
Cisco IOS OSPFv3 Database Display
Router2 show ipv6 ospf database OSPF Router
with ID (3.3.3.3) (Process ID 1)
Router Link States (Area 0) Link ID ADV
Router Age Seq Checksum Link
count 0 1.1.1.1 2009
0x8000000A 0x2DB1 1 0 3.3.3.3
501 0x80000007 0xF3E6 1
Net Link States (Area 0) Link ID
ADV Router Age Seq Checksum 7
1.1.1.1 480
0x80000006 0x3BAD Inter Area
Prefix Link States (Area 0) ADV Router Age
Seq Prefix 1.1.1.1 1761
0x80000005 2001222/64 1.1.1.1
982 0x80000005 20012242/128
Link (Type-8) Link States (Area 0) Link
ID ADV Router Age Seq
Checksum Interface 11 3.3.3.3
245 0x80000006 0xF3DC Lo0 7
1.1.1.1 236 0x80000008 0x68F
Fa2/0 7 3.3.3.3 501
0x80000008 0xE7BC Fa2/0 Intra
Area Prefix Link States (Area 0) Link ID
ADV Router Age Seq Checksum
Ref lstype 0 1.1.1.1 480
0x80000008 0xD670 0x2001 107
1.1.1.1 236 0x80000008 0xC05F
0x2002 0 3.3.3.3 245
0x80000006 0x3FF7 0x2001
17
Cisco IOS OSPFv3 Detailed LSA Display
show ipv6 ospf 1 database inter-area prefix
LS age 1714 LS Type Inter Area Prefix Links
Link State ID 0 Advertising Router 1.1.1.1
LS Seq Number 80000006 Checksum 0x25A0
Length 36 Metric 1 Prefix Address
2001222 Prefix Length 64, Options None
show ipv6 ospf 1 database link
LS age 283 Options (IPv6 Router, Transit
Router, E-Bit, No Type 7-to-5, DC) LS Type
Link-LSA (Interface Loopback0) Link State ID
11 (Interface ID) Advertising Router 3.3.3.3
LS Seq Number 80000007 Checksum 0xF1DD
Length 60 Router Priority 1 Link Local
Address FE802055FFFFEAC1808 Number of
Prefixes 2 Prefix Address 2001113
Prefix Length 64, Options None Prefix
Address 2001113 Prefix Length 64,
Options None
18
OSPFv3 on IPv6 Tunnels over IPv4
interface Tunnel0 no ip address ipv6 address
2001000145A/64 ipv6 address
FE80107BC2ACC910 link-local ipv6 router
ospf 1 area 0 tunnel source Ethernet1 tunnel
destination 10.42.2.1 tunnel mode ipv6ip ! ipv6
router ospf 1
IPv6 Network
IPv6 Tunnel
IPv6 Tunnel
IPv4 Backbone
1
IPv6 Tunnel
IPv6 Network
interface Tunnel0 no ip address ipv6 address
2001000145C/64 ipv6 address
FE80107BC2B28011 link-local ipv6 router
ospf 1 area 0 tunnel source Ethernet2 tunnel
destination 10.42.1.1 tunnel mode ipv6ip ! ipv6
router ospf 1
IPv6 Network
19
References

• RFC 2740 OSPF for IPv6
• RFC 2328 OSPF version 2

20
IGP IS-IS
Not that different form OSPF
21
IGP IS/IS

• OSI in the magic fantasy world everything is
  either an End System (ES) or an Intermediate
  System (IS.)
• ESHosts
• ISRouters
• IS/IS A protocol to let Intermediate Systems
  talk to other Intermediate Systems. IE Router to
  Router. IE Routing
• ISO 10589 specifies OSI IS-IS routing protocol
  for CLNS traffic

22
IGP IS/IS

• IS/IS carries routing information for the OSI
  protocols.
• Type/Length/Value discipline instead of byte code
  for capabilities
• It is also VERY easy to modify to carry other
  protocols, like IPv4 and IPv6.
• The language is different, but the concepts are
  the same as in OSPF (Well, not really, but close
  enough.)
• OSPF AreasIS/IS Levels
• OSPF NeighborsIS/IS Adjacencies
• DR DIS

23
IGP - IS/IS

• Two Level hierarchical architecture Levels Two
  (backbone) and Level One (stub.)

Level 1
Level 2
Level 1
Level 1
Level 1
24
IS-IS Standards

• IETF IS-IS for IP Internets WG
• http//www.ietf.org/html.charters/isis-charter.htm
  l
• ISO 10589 specifies OSI IS-IS routing protocol
  for CLNS traffic
• RFC 1195 added IP support, also known as
  Integrated IS-IS (I/IS-IS)
• I/IS-IS runs on top of the Data Link Layer
• Requires CLNP to be configured
• Draft RFC defines how to add IPv6 address family
  support to IS-IS
• http//www.ietf.org/internet-drafts/draft-ietf-isi
  s-ipv6-05.txt
• Draft RFC introduces Multi-Topology concept for
  IS-IS
• http//www.ietf.org/internet-drafts/draft-ietf-isi
  s-wg-multi-topology-06.txt

25
IS-IS for IPv6

• 2 Tag/Length/Values for IPv6 routing
• IPv6 Reachability TLV (0xEC)
• External bit
• Equivalent to IP Internal/External Reachability
  TLVs
• IPv6 Interface Address TLV (0xE8)
• For Hello PDUs, must contain the Link-Local
  address
• For LSP, must only contain the non-Link Local
  address
• IPv6 NLPID (0x8E) is advertised by IPv6 enabled
  routers

26
Single SPF rules

• single SPF per level for OSI, IPv4 and IPv6
• If IS-IS is used for both IPv4 and IPv6 in an
  area, both protocols must support the same
  topology within this area.
• All interfaces configured with IS-ISv6 MUST
  support IPv6
• All interfaces configured with IS-IS for both
  protocols MUST support both of them
• Otherwise Multi-Topology IS-IS (separate SPF)

27
IS-IS Single Topology
Area C
Area B
Area A
Area D
IPv4-IPv6 enable router
IPv4-only enable router
28
Restrictions from Single SPF

• Not really suitable for an existing IPv4 IS-IS
  network with scattered IPv6 support.
• If IS-IS for both IPv4 and IPv6 then the IPv4 and
  IPv6 topologies MUST match exactly. Cannot run
  IS-IS IPv6 on some interfaces, IS-IS IPv4 on
  others.
• Form adjacencies with similarly-configured
  routers.
• E.g. Problem with An IS-IS IPv6-only router on
  adjacency with an IS-IS IPv4/IPv6 router.
  (Exception is over L2-only interface)
• Cannot join two IPv6 areas via an IPv4-only area.
  L2 adjacencies will form OK but IPv6 traffic will
  black-hole in the IPv4 area.

29
IS-IS Multi Topology
Area C
Area B
Area A
Area D
The Multi-Topology software will create two
topologies inside Area IPv4 and IPv6.
IPv4-only routers will be excluded from the IPv6
topology
IPv4-IPv6 enable router
IPv4-only enable router
30
IGP IS/IS

• Always use Wide Metrics.
• Always set your metrics.
• Always disable Level 1 and force Level 2.
• OSI MTU must be lt 1500.
• You need one Unique OSI address per router.
• An ES-IS state means something is wrong.
• Dont forget It needs OSI/CLNS to work.
• Enable IPv6
• Configure the addresses and
• Ipv6 router isis

31
IGP IS/IS Cisco Interface Config

• interface POS0/0
• description BACKBONE OC48 to IPLSng
• mtu 9180
• ipv6 enable
• ipv6 address
• ip router isis
• ipv6 router isis
• clns mtu 1497

32
IGP IS/IS Cisco Routing

• router isis
• redistribute connected metric-type external
• !
• address-family ipv6
• redistribute connected
• exit-address-family
• net 49.0000.0000.0000.0006.00
• is-type level-2-only
• metric-style wide

33
IGP IS/IS Cisco Commands

• ipls-gsrsh clns neigh
• System Id Interface SNPA
  State Holdtime Type Protocol
• clev-gsr PO2/0 HDLC
  Up 21 L2 IS-IS
• IPLSng PO0/0 HDLC
  Up 26 L2 IS-IS

34
IGP IS/IS Cisco Commands

• ipls-gsrsh isis top
• IS-IS paths to level-2 routers
• System Id Metric Next-Hop
  Interface SNPA
• atla-gsr 588 IPLSng-re0
  PO0/0 HDLC
• chin-gsr 262 IPLSng-re0
  PO0/0 HDLC
• clev-gsr 324 clev-gsr
  PO2/0 HDLC
• dnvr-gsr 1194 IPLSng-re0
  PO0/0 HDLC
• hstn-gsr 1457 IPLSng-re0
  PO0/0 HDLC
• ipls-gsr --
• kscy-gsr 550 IPLSng-re0
  PO0/0 HDLC
• losa-gsr 2850 IPLSng-re0
  PO0/0 HDLC

35
IGP IS/IS Lab

• Bring up IS/IS on your EXTERNAL links.
• Your external interfaces will be advertised by
  IS/IS while your internal interface will be
  advertised by your BGP aggregate.
• Longest Match and Distance/Preference will keep
  things working correctly.

36
Multi-Topology IS-IS

• Multi-Topology IS-IS against the limitations of a
  single SPF process on networks where both IPv4
  and IPv6 topologies cannot be aligned, while
  maintaining the current IS-IS IPv6
  functionalities.
• IS-IS extension by additions of new Type Length
  Value (TLVs).This IS-IS extension impacts
  adjacency forming, prefix advertisement and
  Intermediate Systems reachability.
• Maintenance of 2 topologies, one for IPv6 and one
  common topology for IPv4 and ISO.

37
Multi-Topology IS-IS extensions

• New TLVs attributes for Multi-Topology
  extensions.
• Multi-topology TLV
• MT Intermediate Systems TLV
• Multi-Topology Reachable IPv4 Prefixes TLV
• Multi-Topology Reachable IPv6 Prefixes TLV
• Multi-Topology ID Values
• Multi-Topology ID (MT ID) standardized and in use
  in Cisco IOS
• MT ID 0 standard topology for IPv4/CLNS
• MT ID 2 IPv6 Routing Topology.

38
Multi-Topology IS-IS Restrictions

• NOT compatible with the single SPF model, as new
  TLV are used to transmit and advertise IPv6
  capabilities.
• All routers that run IS-IS for IPv6 are expected
  to enable multi-topology within the network.
• A transition mode (refer to documentation) is
  provided for existing IS-IS IPv6 network to
  migrate to Multi-Topology IS-IS IPv6.
• IPv4, IPv6, or IPv4/IPv6 for either level-1
  level-2 or level-1-2. But if IPv4 and IPv6 are
  configured on the same interface, they must be
  running the same IS-IS level
• Tricky adjacency between Multi topology and
  non multi topology (IPv4 is fine though).
• Wide metric is required to be enabled globally on
  the Autonomous System to run

39
Multi-Topology IS-IS example
Area C
Area B
Area A
Area D
The Multi-Topology software will create two
topologies inside Area IPv4 and IPv6.
IPv4-only routers will be excluded from the IPv6
topology
IPv4-IPv6 enable router
IPv4-only enable router