A: link state routing protocols work process:
Link-state routing protocol 1: flooding of LSAs
routers running link-state routing protocols, interaction between each other is not routing information, but rather LSA (link state advertisement)
What is the link (LINK): router interface
What state (State): describes the relationship between the interface and its neighbor router
Link-state routing protocol 2: LSDB formation
Each router collected LSAs into its own LSDB (link state database) stored. With LSDB, the router is equivalent to master the topology of the entire network
Link State Routing Protocol 3: SPF calculation
each router on the LSDB, using the SPF (Shortest Path Algorithm) has been calculated, with itself as a Root (root), covering the whole network moment acyclic tree
Link State Routing Protocol 4: maintain a routing table
of each router in accordance with the calculation result of SPF, the route loaded into the routing table
Two: OSPF Introduction
Open Shortest Path First, Open Shortest Path First Protocol
. 1: OSPF is a link state routing protocol is described in RFC 2328
2: Open means open public, any vendor can support OSPF, which also makes the OSPF has been widely deployed in the industry
3: OSPF routing protocol priority Intermal (internal) 10; Extermal (external) 150
Three: OSPF basic features
1: adapt to a wide range: the size of the network to support cooperation
2: Fast convergence: Send in the network topology change updates instantly, so that the change is synchronized in the system
3: No Loopback: a route calculation, OSPF shortest path tree algorithm to the collected link states, the algorithm itself ensures that no loops are generated
4: area dividing: allows the network is divided into areas for management. Link state database of the local area and just switch consistent. Reduce link state database of the switch reduces the consumption of memory and CPU usage. Meanwhile, it is necessary to reduce the routing information transmitted between areas, occupied network bandwidth is reduced
5: Equivalent Routing: Supports multiple equal-cost routes to the same destination
Route 6 Rating: Four types of routes. Order of preference are: intra-area routes, inter-area routes, the external route, external route
7: support authentication: supports packet authentication based on regional and interfaces. To ensure the security of packet exchange of
8: multicast transmission: transmitting packets to a multicast address on certain types of links, to reduce interference to other equipment not enabled OSPF
Tris (2) on the OSPF ID Router
. 1: OSPF Router ID for uniquely represents an OSPF router in the OSPF Domain
2: Router ID value of the non-preemptive, first stable
OSPF on the COST
1: Use OSPF cost "cost" as the routing metric
2: OSPF interfaces cost = 100M / interface bandwidth, wherein the OSPF 100M reference bandwidth can be modified
3: OSPF each active interface has a cost value
4: a route cost of the OSPF routing reaches all the way to the sum of all the interfaces of the local cost values from the origin
Four: the three OSPF Table
1: Table neighbor table Use the peer
OSPF routing protocol is a reliable, before requesting transmission between the router LSA, must first OSPF relations are established, Hello packet for discovering a straight-chain connected other OSPF routers on the road, then through a series of interactive news OSPF neighbor relationship eventually establish full border with the neighbor OSPF router information is displayed in the neighbor table
2: link state database Lsdb
With OSPF LSA (Link State Advertisement) to describe the network topology information, then the LSA OSPF routers with these link-state database to store network. OSPF his neighbor advertisement generated and the LSA collected and stored in the LSDB in. LSDB grasp of view as well as in-depth analysis of the LSA to be able to in-depth understanding of OSPF
3: OSPF routing table
based LSDB SPF calculation, the OSPF routing table derived
Five: OSPF packet type
Hello establish and maintain OSPF neighbor relationship
DBD description of the link state database (LSDB described in LSA header information)
LSR link state request, link-state request to OSPF neighbor information
LSU LSU (includes one or more LSA)
the LSAck of the LSU to confirm LSA
Six: OSPF network type of
network types OSPF support: point to point network, broadcast multi-access network, non-broadcast multi-access network (NBMA), P2MP network
Seven: About DR and BDR
Appear background: To reduce the flow OSPF multi-access networks, OSPF will (network access multiplexer) network MA in every election a designated router (DR) and a backup designated router (BDR)
DR election rules: OSPF interface highest priority is selected as DR owner, if the same priority (default 1), has the highest router OSPF Router-ID is elected as DR, and DR having a non-preemptive nature
DR: Designated router, DR is responsible for using the information to update changes to all other OSPF routers (Drother)
BDR: backup designated router, BDR monitors the DR of the state and take over its role in the current DR fails
questions:
1: What is the DR and BDR?
A: DR is the designated router on a broadcast or NBMA network segment, and for other routers adjacency relationship, exchange routing information.
BDR is the backup designated router on a broadcast or NBMA network segment, and for other routers and DR adjacency relationship, exchange routing information. Backup router as the DR, when the DR fails, the BDR will automatically become DR.
2: Router Priority must be a maximum of DR do?
A: Not necessarily, in order to maintain the stability of adjacency relationships, topology changes (not involved in the current DR and BDR) will not lead to the re-election of DR and BDR.
Modify priority command DR: [R G0 / 0/0 ] OSPF dr-priority "number"
Eight: The concept (area) of OSPF the AREA
(a): the existence of a single regional issues:
1: LSA flooding is serious, the burden of OSPF routers lot
2: internal regional instability will cause the whole network is calculated by the SPF's
3: LSDB huge. Excessive consumption of resources. Equipment performance degradation, affecting the forwarding
4: Each router needs to maintain routing tables growing, a single routing area can not be aggregated
(b) OSPF multi-area
1: Reduce the scope of LSA flooding, effectively change the topology control in the area, the purpose of network optimization
2: at the zone boundaries can do route summarization, reduces routing table
3: characteristics of the full use of OSPF special areas, to further reduce LSA flooding, to optimize the network
4: multi region improves network scalability, conducive to the formation of large-scale network