Link State Routing. In particular OSPF. Karst Koymans. Informatics Institute University of Amsterdam. (version 16.3, 2017/03/09 11:25:31)

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1 Link State Routing In particular OSPF Karst Koymans Informatics Institute University of Amsterdam (version 16.3, 2017/03/09 11:25:31) Tuesday, March 7, 2017 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

2 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

3 Link State Protocols Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

4 Link State Protocols Basic ideas Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

5 Link State Protocols Basic ideas Link State Protocol A Link State Protocol Builds on complete information about the network topology Uses Dijkstra s Single Source Shortest Path Tree algorithm Replaces a distance vector protocol in the case of more complex topologies Has a faster convergence time than distance vector protocols Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

6 Link State Protocols Basic ideas Link State Packets Link State Packets (LSPs) represent the state of a router and its links to the rest of the network This representation would suffice for point to point links Broadcast networks (LANs) and NBMA networks are represented by virtual nodes inside the topology Designated routers (DRs) speak on their behalf Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

7 Link State Protocols Basic ideas Non-broadcast networks NBMA Non-Broadcast Multiple Access Full mesh of connectivity, but not all at once in one packet Topological connectivity via elected DR Point-to-Multipoint A subset of the collection of all point-to-point links No full mesh of connectivity Considered as multiple instances of point-to-point links Hence no DR is elected Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

8 Link State Protocols Basic ideas Learn to know your neighbours Easy on point to point links Just send out greetings (hello packets) Both ends will become adjacent A little more advanced on broadcast networks Send out hello packets using multicast Not all neighbours will become adjacent Only those that are neighbors in the virtual topology One of the adjacent routers is always a DR Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

9 Link State Protocols Basic ideas LSP generation Periodic announcements with a long period (like 30 minutes) Very much different from RIP (30 seconds) Triggered updates are sent as soon as there are changes Detection of a new neighbour (link or node coming up) Detection of a link or node failure Change of link cost Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

10 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

11 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Distribution can t use the routing database for distant nodes Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

12 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Distribution can t use the routing database for distant nodes Why? What is the difference with RIP here? Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

13 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Distribution can t use the routing database for distant nodes Why? What is the difference with RIP here? Ordinary flooding is problematic..., why? Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

14 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Distribution can t use the routing database for distant nodes Why? What is the difference with RIP here? Ordinary flooding is problematic..., why? It would need a TTL to prevent loops Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

15 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Distribution can t use the routing database for distant nodes Why? What is the difference with RIP here? Ordinary flooding is problematic..., why? It would need a TTL to prevent loops It could cause exponential multiplication of packets Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

16 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Distribution can t use the routing database for distant nodes Why? What is the difference with RIP here? Ordinary flooding is problematic..., why? It would need a TTL to prevent loops It could cause exponential multiplication of packets Smart flooding recognizes identical LSPs Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

17 Link State Protocols Basic ideas LSP distribution LSPs are distributed throughout the network Distribution can t use the routing database for distant nodes Why? What is the difference with RIP here? Ordinary flooding is problematic..., why? It would need a TTL to prevent loops It could cause exponential multiplication of packets Smart flooding recognizes identical LSPs Causing propagation to be tree-like Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

18 Link State Protocols Problems and pitfalls Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

19 Link State Protocols Problems and pitfalls Most recent LSP problem Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

20 Link State Protocols Problems and pitfalls Most recent LSP problem LSPs may arrive out of order Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

21 Link State Protocols Problems and pitfalls Most recent LSP problem LSPs may arrive out of order Therefore we need a mechanism to recognize older packets Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

22 Link State Protocols Problems and pitfalls Most recent LSP problem LSPs may arrive out of order Therefore we need a mechanism to recognize older packets What mechanisms are available for this recognition? Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

23 Link State Protocols Problems and pitfalls Most recent LSP problem LSPs may arrive out of order Therefore we need a mechanism to recognize older packets What mechanisms are available for this recognition? What about using timestamps? Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

24 Link State Protocols Problems and pitfalls Most recent LSP problem LSPs may arrive out of order Therefore we need a mechanism to recognize older packets What mechanisms are available for this recognition? What about using timestamps? Timestamps cause trouble if clocks are not synchronised or out of order! Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

25 Link State Protocols Problems and pitfalls Most recent LSP problem LSPs may arrive out of order Therefore we need a mechanism to recognize older packets What mechanisms are available for this recognition? What about using timestamps? Timestamps cause trouble if clocks are not synchronised or out of order! What about using sequence numbers? Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

26 Link State Protocols Problems and pitfalls Most recent LSP problem LSPs may arrive out of order Therefore we need a mechanism to recognize older packets What mechanisms are available for this recognition? What about using timestamps? Timestamps cause trouble if clocks are not synchronised or out of order! What about using sequence numbers? Sequence numbers need an ageing procedure to protect from stale information for instance when a router reboots and starts from scratch Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

27 Pitfalls Sequence numbers may wrap Sequence number ordering is not a total ordering, not even a partial ordering a < b < c < d < e < f < g < h < a

28 Link State Protocols Problems and pitfalls Intermezzo The devilish dice There are three dice, A, B and C such that A is better than B B is better than C C is better than A Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

29 Link State Protocols Problems and pitfalls Intermezzo The devilish dice There are three dice, A, B and C such that A is better than B B is better than C C is better than A A: Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

30 Link State Protocols Problems and pitfalls Intermezzo The devilish dice There are three dice, A, B and C such that A is better than B B is better than C C is better than A A: B: Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

31 Link State Protocols Problems and pitfalls Intermezzo The devilish dice There are three dice, A, B and C such that A is better than B B is better than C C is better than A A: B: C: Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

32 ARPANET lockup (real historic event 1 ) Suppose we have sequence numbers a, b, c with a < b < c < a Why didn t ageing do its job? 1 According to Radia Perlman in the Interconnections book

33 Link State Protocols Problems and pitfalls Lockup solution Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

34 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

35 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field which will be increased (or decreased) periodically Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

36 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field which will be increased (or decreased) periodically and always increase the age (decrease the ttl) by at least one when passing the LSP on Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

37 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field which will be increased (or decreased) periodically and always increase the age (decrease the ttl) by at least one when passing the LSP on Forgetting this was the main problem in the total ARPANET lockup Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

38 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field which will be increased (or decreased) periodically and always increase the age (decrease the ttl) by at least one when passing the LSP on Forgetting this was the main problem in the total ARPANET lockup Use a very large sequence number space Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

39 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field which will be increased (or decreased) periodically and always increase the age (decrease the ttl) by at least one when passing the LSP on Forgetting this was the main problem in the total ARPANET lockup Use a very large sequence number space and wait for timeouts after overflow Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

40 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field which will be increased (or decreased) periodically and always increase the age (decrease the ttl) by at least one when passing the LSP on Forgetting this was the main problem in the total ARPANET lockup Use a very large sequence number space and wait for timeouts after overflow while reflooding LSPs with maximum age Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

41 Link State Protocols Problems and pitfalls Lockup solution Use an age (or ttl) field which will be increased (or decreased) periodically and always increase the age (decrease the ttl) by at least one when passing the LSP on Forgetting this was the main problem in the total ARPANET lockup Use a very large sequence number space and wait for timeouts after overflow while reflooding LSPs with maximum age Causing those to time out prematurely Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

42 OSPF Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

43 OSPF Rationale Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

44 OSPF Rationale OSPF advantages (1) OSPF Introduces hierarchical routing Supports subnets Uses efficient multicast for flooding Supports point-to-point, broadcast, NBMA and point-to-multipoint networks Uses metrics built on cost, per interface Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

45 OSPF Rationale OSPF advantages (2) OSPF Supports virtual links for backbone connectivity Supports load balancing Supports unnumbered interfaces/networks Has built in authentication Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

46 OSPF Rationale OSPF fun :) IETF T-shirt IS IS = 0 The old time IETF versus ISO controversy But OSPF in fact really builds on BBN s research on SPF Early versions of OSI s IS-IS Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

47 OSPF Rationale Some OSPF facts OSPF builds directly upon IP (not on UDP) OSPF uses protocol type 89 Current OSPF version is 2 RFC 2328 (Moy, 1998) RFC 2740 (OSPF for IPv6, 1999) version 3 Obsoleted by RFC 5340 (2008) OSPF uses LSA (Link State Advertisement) terminology instead of LSP (Link State Packet) Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

48 OSPF Parameters Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

49 OSPF Parameters Timers and Overflow These must be the same for all OSPF neighbours Otherwise the neighbours won t talk at all HelloInterval (default 10 sec) RouterDeadInterval (default 40 sec) In the case of a database overflow external routing information is dropped first Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

50 OSPF Databases Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

51 OSPF Databases Consistent LSA Databases LSAs must be acknowledged LSAs (and their acks) are queued/flagged for transmission LSAs must time out at about the same time by using triggered (re)distribution of age MaxAge packets for LSAs with an existing sequence number which must be honored only if there is already an LSA for this node in the local database Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

52 OSPF Network representation and architecture Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

53 OSPF Network representation and architecture (Backup) Designated Router A Designated Router (DR) and a Backup Designated Router (BDR) is elected on every multi-access network using Hello packets The (B)DR represents the network as a virtual node in the graph and acts on the network s behalf The DR/BDR election process is sticky This is one of the main differences with IS-IS The priority of routers can be configured Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

54 Multicast usage On LANs every router becomes adjacent to the Designated Router Multicast 2 to AllDRouters ( ) Multicast 2 to AllSPFRouters ( ) There is also a unicast Ack from the DR back to R 2 OSPFv3 for IPv6 uses FF02::6 and FF02::5

55 Hierarchical routing Area 0 is the backbone area Limbs (non-backbone) are all other areas, not equal to 0

56 Virtual Links Area 5 is not physically connected to the backbone A virtual link extends the backbone to the new ABR and behaves as an unnumbered point to point link

57 OSPF Network representation and architecture Inter Area Summary (IAS) IASs are injected by ABRs IASs make use of a hub and spoke topology Summary information is spread RIP-like There are no loops or slow convergence Virtual links maintain the hub and spoke topology These virtual spokes are in fact paths through their transit area treated as unnumbered links in the backbone Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

58 OSPF Network representation and architecture Router roles Backbone router Has at least one interface inside area 0 Internal router All interfaces are completely within a single area (backbone or otherwise) Area Border Router (ABR) Has an interface inside area 0 and one or more other areas Autonomous System Boundary Router (ASBR) Participates in another (external) routing protocol Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

59 OSPF Network representation and architecture Area Border Router (ABR) Attaches to multiple areas Runs multiple copies of the basic algorithm One copy for each area Summarizes area data (destination networks) towards the backbone Receives summarized data from the backbone about other areas including the backbone itself Can aggregate summary data Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

60 OSPF Network representation and architecture Autonomous System Boundary Router (ASBR) Can be part of any area Interfaces with other routing protocols BGP, RIP, IS-IS, OSPF,... Injects external routes into OSPF ASBR notion is independent of backbone, internal or ABR router Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

61 OSPF Network representation and architecture Stub(by) area A stub(by) area is an area into which no external routing information is injected by the ABRs It uses a default route for all external destinations The default route is injected by all ABRs A totally stubby area is a stubby area into which not even inter-area summaries are injected A not so stubby area is a stubby area inside which certain external information is originated and flooded locally Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

62 OSPF packet details Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

63 OSPF packet details OSPF packet header Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

64 OSPF packet details OSPF packet header OSPF packet header (24 bytes) Version Type Packet length Router ID Area ID Checksum AuType Authentication Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

65 OSPF packet details OSPF packet header OSPF packet header fields OSPF packet header fields Version 2 Type Packet length Router ID Area ID Checksum AuType Authentication 1 5 (see next slide) Total length, including this header ID of packet sending router The area a packet belongs to (is destined for) One s complement checksum Null, Simple or Crypto Pointer to message digest (Crypto) Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

66 OSPF packet details OSPF packet header OSPF packet types OSPF packet types Type Meaning 1 Hello 2 Database Description 3 Link State Request 4 Link State Update a 5 Link State Acknowledgement b a These contain the Link State Advertisements b Don t confuse these with LSAs Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

67 OSPF packet details The different types of OSPF packets Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

68 OSPF packet details The different types of OSPF packets OSPF Hello packet (20 + N 4 bytes) Network Mask HelloInterval Options Rtr Pri RouterDeadInterval Designated Router Backup Designated Router Neighbor #1. Neighbor #N Repeated for each neighbor that is alive Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

69 OSPF packet details The different types of OSPF packets a Deprecated because of lack of experience with TOS Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85 OSPF Hello packet fields Hello fields Network Mask HelloInterval Options Rtr Pri RouterDeadInterval Designated Router Backup Designated Router Neighbor Subnet mask of link Interval in seconds between hello packets Multiple metrics (T a ); no stub area (E) Router priority, used for DR election Interval to consider a silent neighbor dead IP address of designated router IP address of backup designated router Living neighbor IDs

70 OSPF packet details The different types of OSPF packets OSPF DD packet (8 + N 20 bytes) Interface MTU Options I M M S DD sequence number LSA header #1. LSA header #N Fragment of database with only headers Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

71 OSPF packet details The different types of OSPF packets OSPF DD packet fields DD fields Interface MTU Options I M MS DD sequence number LSA header Detection of MTU mismatch Same as for Hello packets Init bit (first packet) More bit (more packets follow) Master/Slave bit Used for recognizing old DD packets Link state database LSA instance identity a a Specific LSA instance, including age and sequence number Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

72 OSPF packet details The different types of OSPF packets OSPF LS request packet (N 12 bytes) 0 31 LS type Link State ID Advertising Router Multiple occurrences Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

73 OSPF packet details The different types of OSPF packets OSPF LS request packet fields LS request fields LS type Link State ID Advertising Router Link type of the LSA ID of (link type specific part of) the LSA Router ID of originating router These three fields are part of the LSA header. Note that these request packets do not include an age or sequence number. Together these entries uniquely identify an LSA, but not an LSA instance. The Database Description packets refer to a specific LSA instance, but still without actual data. Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

74 OSPF packet details The different types of OSPF packets OSPF LS Update packet 0 31 # LSAs (N) LSA #1 N occurrences LSA #N Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

75 OSPF packet details The different types of OSPF packets OSPF LS Update packet fields LS Update fields # LSAs Number of LSAs inside the update packet LSA #i A complete Link State Advertisement Link State Updates contain complete and specific instances of Link State Advertisements (LSAs) with all relevant data. The LSAs have a variable size, depending on LS type. Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

76 OSPF packet details The different types of OSPF packets OSPF LS Acknowledgement packet (N 20 bytes) 0 31 LSA header #1 N occurrences LSA header #N Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

77 OSPF packet details The different types of OSPF packets OSPF LS Acknowledgement packet fields LS Acknowledgement fields LSA header #i A complete Link State Advertisement header Link State Acknowledgements again refer to specific instances, but contain no actual data. Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

78 OSPF packet details Link State Advertisement packets Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

79 OSPF packet details Link State Advertisement packets Link State Advertisements Multiple LSAs may be found inside a Link State Update packet Every LSA consists of LSA header (20 bytes) LS(A) type specific content Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

80 OSPF packet details Link State Advertisement packets LSA header (20 bytes) LS age Options LS type Link State ID Advertising Router LS sequence number LS Checksum Length Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

81 OSPF packet details Link State Advertisement packets LSA header fields LSA header fields LS age Options LS type Link State ID Advertising Router LS sequence number LS Checksum Length Time in seconds since the LSA was originated Same as for Hello packets Link type of the LSA (see next slide) ID of (link type specific part of) the LSA Router ID of originating router Used for most recent check of LSA packets The Fletcher checksum of the LSA (without age) Length in bytes of the LSA, including the header Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

82 OSPF packet details Link State Advertisement packets LS types LS types LS Type Meaning 1 Router LSA 2 Network LSA 3 Network Summary LSA 4 AS Boundary Router Summary LSA 5 AS External LSA 7 NSSA LSA (see next slide) Topological (1,2), prefix (3,5,7) and mixed (4) information Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

83 OSPF packet details Link State Advertisement packets NSSA NSSA stands for Not So Stubby Area Support for certain external routes throughout the area itself NSSA uses its own special type (7) These LSAs are translated at the ABR into ordinary external LSAs (type 5) for the rest of the OSPF domain It is common to inject a type 7 default route from the NSSA boundary router(s) into the NSSA Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

84 OSPF packet details Link State Advertisement packets Link State IDs Link State IDs LS Type Link State ID meaning 1 ID of originating router 2 IP address of the network s DR 3 The destination network s prefix 4 ID of described ASBR 5 The destination network s prefix 7 The destination network s prefix Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

85 OSPF packet details Link State Advertisement packets Link State IDs Link State IDs LS Type Link State ID meaning 1 ID of originating router 2 IP address of the network s DR 3 The destination network s prefix 4 ID of described ASBR 5 The destination network s prefix 7 The destination network s prefix Router LSA Link State ID Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

86 OSPF packet details Link State Advertisement packets Router LSA (LS type = 1) without header repeated # Links times V E B 0 # Links Link ID Link Data Type # TOS Metric } TOS 0 TOS metric # TOS times 3 Originated by every router Flooded throughout the area(s) the router belongs to 3 For backward compatibility (but never really implemented or used) Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

87 OSPF packet details Link State Advertisement packets Router LSA fields Router LSA fields V Router is virtual link endpoint E Router is AS Boundary Router B Router is Area Border Router # Links Number of router links described Link ID ID of the connected network Link Data Extra information on network Type Type of connected network # TOS Number of extra TOSs (usually 0) Metric Cost of link Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

88 OSPF packet details Link State Advertisement packets Router LSA type field Router LSA type field Type Meaning 1 Point-to-point link 2 Transit network 3 Stub network 4 Virtual link Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

89 OSPF packet details Link State Advertisement packets Router LSA Link ID field Router LSA Link ID field Type Meaning 1 ID of neighbor router 2 IP address of designated router 3 IP (sub)network number a 4 ID of neighbor router a This can also be a host (with a /32 mask in the link data) Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

90 OSPF packet details Link State Advertisement packets Router LSA Link Data field Router LSA Link Data field Type Meaning 1 Originating router s interface IP address 2 Originating router s interface IP address 3 Connected (sub)network mask 4 Originating router s interface IP address Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

91 OSPF packet details Link State Advertisement packets Link State IDs Link State IDs LS Type Link State ID meaning 1 ID of originating router 2 IP address of the network s DR 3 The destination network s prefix 4 ID of described ASBR 5 The destination network s prefix 7 The destination network s prefix Network LSA Link State ID Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

92 OSPF packet details Link State Advertisement packets Network LSA (LS type = 2) without header 4 + N 4 bytes 0 31 Network Mask Attached Router } Repeated for each attached router Originated by Designated Router Flooded throughout the area Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

93 OSPF packet details Link State Advertisement packets Network LSA fields Network LSA fields Network Mask Attached Router (Sub)network mask a Router ID of router(s) on network a Where is the network itself defined? Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

94 OSPF packet details Link State Advertisement packets Link State IDs Link State IDs LS Type Link State ID meaning 1 ID of originating router 2 IP address of the network s DR 3 The destination network s prefix 4 ID of described ASBR 5 The destination network s prefix 7 The destination network s prefix Summary LSA Link State ID Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

95 OSPF packet details Link State Advertisement packets Summary LSA (type = 3, 4) without header Network Mask 4 0 Metric } TOS TOS metric for each desired TOS Originated by Area Border Router Flooded throughout the area(s) 4 Only relevant for type 3 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

96 OSPF packet details Link State Advertisement packets Summary LSA fields Summary LSA fields Network Mask a Metric Address mask for the advertised destination Cost to advertised destination a Only relevant for type 3 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

97 OSPF packet details Link State Advertisement packets Link State IDs Link State IDs LS Type Link State ID meaning 1 ID of originating router 2 IP address of the network s DR 3 The destination network s prefix 4 ID of described ASBR 5 The destination network s prefix 7 The destination network s prefix External LSA Link State ID Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

98 OSPF packet details Link State Advertisement packets AS External LSA (LS type 5) without header Network Mask E 0 Metric Forwarding address External Route Tag E TOS TOS metric Forwarding address External Route Tag for each desired TOS Originated by AS Boundary Router Flooded throughout the whole AS Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

99 OSPF packet details Link State Advertisement packets AS External LSA fields AS External LSA fields Network Mask E Metric Forwarding address External Route Tag Address mask for the advertised destination External cost is higher than internal cost Cost to advertised destination Comparable to Next Hop in RIP Comparable to Route Tag in RIP Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

100 Representation of routers and networks Source: RFC 2328

101 Representation of point to multipoint networks Source: RFC 2328

102 Example OSPF network from RFC 2328 Source: RFC 2328

103 The directed graph for the example network Source: RFC 2328

104 The shortest path tree from router RT6 Source: RFC 2328

105 Router (RT12) and network (N9) LSAs Source: RFC 2328

106 OSPF for IPv6 Outline 1 Link State Protocols Basic ideas Problems and pitfalls 2 OSPF Rationale Parameters Databases Network representation and architecture 3 OSPF packet details OSPF packet header The different types of OSPF packets Link State Advertisement packets 4 OSPF for IPv6 Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

107 OSPF for IPv6 OSPF for IP version 6 Also referred to as OSPFv3 Published as RFC 5340 Extensive, incompatible modification of OSPFv2 Therefore needs a new version number (3) Basic functionality is the same Flooding, areas, SPT, DRs,... Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

108 OSPF for IPv6 Important changes All addressing semantics moved to LSA payload Works per-link instead of per-subnet Introduces a new link-lsa Introduces explicit flooding scope Link scope, Area scope and AS scope Removes authentication from packet header Authentication uses AH and ESP headers Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

109 OSPF for IPv6 Router and network LSAs Do not contain address information any more Only topological connectivity No IPv6 prefix information Network protocol independent Prefix information on transit and stub networks is inside a new intra-area-prefix-lsa Link-LSAs now distribute Link local addresses of routers IPv6 prefixes used on the link Option announcements for network LSAs Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85

110 OSPF for IPv6 LSA renamings Type-3 summary-lsas are now called inter-area-prefix-lsas Type-4 summary LSAs are now called inter-area-router-lsas Karst Koymans (UvA) Link State Routing Tuesday, March 7, / 85