Transcript 2007 LAN Product Stategy & Roadmap - D-Link
Open Shortest Path First
Pedro Tsao
E-mail:[email protected]
Agenda
Link state
OSPF Areas
OSPF behavior
OSPF Packets Type
OSPF Network Type
OSPF LSA Type
OSPF Route Summarization
Configuring OSPF Special Area types
Configuring OSPF Authentication
Link State
Link State
The information available to a distance vector router has been compared to the information available from a road sign . Link state routing protocol are like a road map .
Link State routing include the following: • Open Shortest Path First (OSPF) for IP • The ISO’s Intermediate System-to-Intermediate System (IS-IS) for CLNS and IP • DEC’s DNA Phase V • Novell’s NetWare Link Services Protocol (NLSP)
OSPF as a Link-State Protocol
• OSPF propagates link-state advertisements rather than routing table updates • LSAs are flooded to all OSPF routers in the area • The OSPF link-state database(LSDB) is pieced together from the LSAs generated by the OSPF routers • OSPF use the SPF algorithm to calculate the shortest path to a destination Link = router interface State = description of an interface and its relationship to neighboring routers
Link State Data Structures
– Neighbor table: Also known as the adjacency database Contains list of recognized neighbors – Topology table: Typically referred to as LSDB Contains all routers and their attached links in the area or network Identical LSDB for all routers within an area – Routing table: Commonly named a forwarding database Contains list of best paths to destinations
Link State Routing Protocol
Link-state routers recognize more information about the network than their distance vector counterparts. Each router has a full picture of the topology .
Consequently, link-state routers tend to make more accurate decisions.
OSPF Areas
Link State Data Structure: Network Hierarchy
Link-state routing requires a hierachical network structure that is enforced by OSPF.
This two-level hierarchy consists of the following: • Transit area (backbone or area 0) • Regular areas (non-backbone areas)
OSPF Areas
OSPF area characteristics: Minimizes routing table entries Localizes impact of a topology change within an area Detailed LSA flooding stops at the area boundary Requires a hierarchical network design Area1 Backbone Area Area2 Area3
OSPF Terminology
Router A and B are backbone routers Backbone routers make up area 0 Router C, D and E are known as Area Border Routers (ABRs) ABRs attach all other areas to area 0 Area1 Backbone Area Area2 Area3
OSPF Behavior
OSPF Adjacencies
Hello Routers discover neighbors by exchange hello packets Routers declare neighbors to be up after checking certain parameters or options in the hello packet
Forming OSPF Adjacencies
Point-to-point WAN links: Both neighbors become full adjacent LAN Links Neighbors form a full adjacency with the DR and BDR Routers maintain two-way state with the other routers (DROTHERs) Routing updates and topology information are passed only between adjacent routers Once an adjacency is formed, LSDBs are synchronized by exchanging LSAs LSAs are flooded reliably through the area (or network)
OSPF Router ID
The Router is Known to OSPF by the OSPF router ID number LSDBs use the OSPF router ID to differentiate one router from the next In descending other of specificity, the Router-id may be one of following: • Router-id command • Highest loopback address • Highest Active IP address
OSPF DR/BDR Election
DR/BDR will be electing by the following rules: • The router With Highest priority value is the DR • The router with the second highest priority value is BDR • In case of a tie. The highest Router ID is DR, the second is BDR • A router with priority of 0 cannot be the DR or BDR • A router that’s not DR or BDR is a DROther • If a router with higher priority comes into the network, it does not preempt the DR or BDR
OSPF Calculation
Routers find the best paths to destinations by applying Dijkstra’s SPF algorithm to link state database as follows: Every router in an area has the identical link-state DB Each router in the area places itself into the root of the tree that is built The best path is calculated with respect to the lowest total cost of links to a specific destination Best routes are put into the forwarding database(routing table)
OSPF Calculation(cont.)
Link-state DB A D x E Shortest Path C B A Dijkstra’s algorithm D F G H F Assume all links are Ethernet, with an OSPF cost of 10 G x E H C B
OSPF Packets Type
OSPF Packet Types
1.Hello
2.Destination Description 3.Link-State Request 4.Link-State Update 5.Link-State Acknowledgement
Neighborship: The Hello Packet
Hello hello • Router ID • Hello and dead intervals • Neighbors • Area ID • Router priority • DR IP address • BDR IP address • Authentication password • Stub area flag • Entry must match on neighboring routers
Establishing Bidirectional Communication
hello A 172.16.5.1/24 Port1 Down state I am router id 172.16.5.1, and I see no one Port2 172.16.5.2/24 B To 224.0.0.5
Initial State Router B neighbor List 172.16.5.1/24,in Port2 Unicast to A I am router id 172.16.5.2, and I see 172.16.5.1
Router A neighbor List 172.16.5.2/24,in Port1 hello Two-way State
Discovering the Network Routes
A 172.16.5.1/24 Port1 Port2 172.16.5.2/24 B DBD Exstart state I will start exchange because I have router id 172.16.5.1
No, I’ll start exchange because I have a higher RID DBD DBD exchange State Here is a summary of my LSDB Here is a summary of my LSDB DBD
Adding the Link-State Entries
A 172.16.5.1/24 Port1 Port2 172.16.5.2/24 LSAck Thanks for the information!
Loading state LSR LSAck I need complete entry for network 172.16.6.0/24 Here is the entry for network 172.16.6.0/24 Thanks for the information!
Full State B LSAck LSU
Case Study: OSPF Packets
Area 0 int1 172.17.1.1/24 int2 172.17.2.1/24 Router ID: 2.2.2.2
int1 10.1.1.3/24 Router ID: 1.1.1.1
System 10.1.1.2/24 int1 192.168.1.1/24 Area 2 int2 192.168.2.1/24
Link-State Data Structures: LSA Operation
LSA IS entry in LSDB?
NO Add to DB YES YES Is seq# the same?
NO Is seq# higher?
Send LSAck NO YES Flood LSA Send LSU with newer information to source Ignore LSA Run SPF to calculate new routing table END END
Maintaining Routing Information
3 DR 1 2 B A Router A notifies all OSPF DRs on 224.0.0.6
DR notifies others on 224.0.0.5
Command (OSPF)
Command
Enable ospf Disable ospf create ospf area create ospf host_route create ospf aggregation config ospf ipif create ospf virtual_link
Parameters
Case Study: OSPF Configuration(D-Link)
Router ID: 2.2.2.2
DES-3852 Area 0 int1 172.17.1.1/24 int2 172.17.2.1/24 System 10.1.1.3/24 Router ID: 1.1.1.1
DES-3828P System 10.1.1.2/24 int1 192.168.1.1/24 Area 2 int2 192.168.1.1/24
int1 172.17.1.1/24 DES-3852 # OSPF config ospf ipif System area 0.0.0.0 state enable config ospf ipif int1 area 0.0.0.0 state enable config ospf ipif int2 area 0.0.0.0 state enable config ospf router_id 2.2.2.2
enable ospf System 10.1.1.3/24 int2 172.17.2.1/24 System 10.1.1.2/24 DES-3828P # OSPF create ospf area 0.0.0.2 type normal config ospf ipif System area 0.0.0.0 state enable config ospf ipif int1 area 0.0.0.2 state enable config ospf ipif int2 area 0.0.0.2 state enable config ospf router_id 1.1.1.1
enable ospf int1 192.168.1.1/24 int2 192.168.1.1/24
int1 172.17.1.1/24 DES-3852 # OSPF config ospf ipif System area 0.0.0.0 state enable config ospf ipif int1 area 0.0.0.0 state enable config ospf ipif int2 area 0.0.0.0 state enable config ospf router_id 2.2.2.2
enable ospf System 10.1.1.3/24 int2 172.17.2.1/24 System 10.1.1.2/24 DES-3828P # OSPF create ospf area 0.0.0.2 type normal config ospf ipif System area 0.0.0.0 state enable config ospf ipif int1 area 0.0.0.2 state enable config ospf ipif int2 area 0.0.0.2 state enable config ospf router_id 1.1.1.1
enable ospf int1 192.168.1.1/24 int2 192.168.1.1/24
int1 172.17.1.1/24 DES-3852 # OSPF config ospf ipif System area 0.0.0.0 state enable config ospf ipif int1 area 0.0.0.0 state enable config ospf ipif int2 area 0.0.0.0 state enable config ospf router_id 2.2.2.2
enable ospf System 10.1.1.3/24 int2 172.17.2.1/24 System 10.1.1.2/24 DES-3828P # OSPF create ospf area 0.0.0.2 type normal config ospf ipif System area 0.0.0.0 state enable config ospf ipif int1 area 0.0.0.2 state enable config ospf ipif int2 area 0.0.0.2 state enable config ospf router_id 1.1.1.1
enable ospf int1 192.168.1.1/24 int2 192.168.1.1/24
Case Study: OSPF Configuration(Cisco)
Fa1/3 10.1.3.2/24 SW3 Area 0 Fa1/1 88.88.88.88/24 Area 1 Fa1/1 172.31.1.2/24 Fa1/2 10.1.2.1/24 SW2 Fa1/1 172.31.1.1/24 Fa1/2 10.1.2.1/24 SW4 Fa1/2 99.99.99.99/24 SW1 Fa1/3 10.1.3.1/24 Area 3 • X is the Switch Number • Each Switch has a loopback: X.X.X.X/32 except SW3
OSPF Network Type
OSPF Network Type
The three types of networks defined by OSPF are: Point-to-point : A network that joins a single pair of routers Broadcast : A multiaccess broadcast network, such as Ethernet Non-Broadcast multiaccess(also called NBMA) : A network that interconnects more than two routers but that has no broadcast capability. Frame Relay, X.25 and ATM are examples of NBMA networks
Point-to-point Links
Usually a serial interface running either PPP or HDLC May also be a point-to-point interface running Frame Relay or ATM No DR or BDR election required OSPF autodetects this interface type OSPF packets are send using multicast 224.0.0.5
Broadcast Network
Generally these are LAN technologies like Ethernet and Token Ring DR and BDR election are required All neighbor routers form full adjacencies with the DR and BDR only Packets to the DR and BDR use 224.0.0.6
Packets from DR to all other routers use 224.0.0.5
Electing the DR and BDR
Hello Hello packets are exchange via IP multicast The router with the highest priority is selected as the BR. The second-highest one is the BDR Use the OSPF RID as the tie breaker The DR election is nonpreemptive
OSPF Network Type summary
OSPF Mode Broadcast Nonbroadcast (NBMA) NBMA Preferred Topology Full or partial mesh Full or partial mesh Subnet Address Same Same Hello Timer 10 sec 30 sec Point-to multipoint Partial-mesh or star Same 30 Sec Point-to multipoint nonbroadcast Point-to-point partial-mesh or star Partial-mesh or star, using subinterface Same 30 sec Different for Each Subinterface 10 sec Adjacency Automatic, DR/BDR elected Manual configuration, DR/BDR elected Automatic, no DR/BDR Manual configuration, no/DR/BDR Automatic, no DR/BDR RFC or Cisco Cisco RFC RFC Cisco Cisco
OSPF Router Type
Internal routers ABR and Backbone Area0 Backbone/Internal routers Router Internal routers Area1 ABR and Backbone Router External AS Area2 ASBR and Backbone Router
OSPF Virtual Link
Area0 10.0.0.0
A Area1 172.16.0.0
Virtual Link B Area0 10.0.0.0
• Virtual links are used to connect a discontinuous area to area 0 • A logical connection is built between router A and router B • Virtual links are recommended for backup or temporary connections
Case Study: OSPF Virtual Link (D-Link)
Case Study: OSPF Virtual Link (Cisco)
Q&A
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