A, OSPF adjacency condition becomes established from the neighbors:
------ be distinguished based on the network type;
an interface network: the network type is determined, based on Layer 2 encapsulation technique to a device interface;
1 point: There is only two nodes in a network segment, even if the third positive connection point, normal communication can not be finally;
serial link, Layer 2 encapsulation is not hdlc- ppp or physical addressing.
2.MA: Multiple Access - the number of nodes on a network segment is not limited;
3.BMA: broadcast type multiple access technology; broadcast mechanism is present at the same time a MA network;
Layer 2 encapsulation Ethernet technology.
4.NBMA: Non-broadcast type multiplexing technique; no broadcast mechanism in a MA network;
Layer 2 encapsulation technology FR - serial link MGRE,
在点到点网络中，OSPF协议正常均从邻居关系晋升为邻接关系；
在MA网络中，若所有邻居皆建立为邻接关系，将导致大量的重复更新；距离矢量路由协议在MA环境中使用了接口水平分割机制；由于OSPF协议是基于数据库同步对比的方式来进行收敛，故不支持接口的水平分割；
ospf最终将在MA网段进行DR/BDR的选举；非DR/BDR间将维持邻居关系，不建立邻接关系来避免重复更新；
DR / BDR election rules:
Comparative interface priority 0-255 more preferably greater;
default point link interfaces without DR / BDR election, so Cisco priority candidate is not 0 ----
MA network all candidates Interface default priority is 1, the device must candidate route-id in case the same priority, preferably a large value.
Interference election: election to modify the priority of the interface;
[R1-the GigabitEthernet0 / 0/0] ospf priority DR-2
because the election non-preemptive, priority after it is modified, the process must be restarted ospf protocol
RESET ospf. 1 Process
Warning: the OSPF of The Process will be reset Continue [Y / N ]:.? y
Recommendation: the presence of DR / BDR after the network, other devices modified to 0, not to stand; do not need to restart the process equipment.
Two, OSPF database table link state database tables ---- the LSDB
database tables loaded different types of OSPF LSA;
[R1] the display of a specific OSPF LSDB the LSA Router 1.1.1.1
category name link-id
for each LSA average the following information
Type: Router category name
Ls id: 1.1.1.1 link-id in the catalog designation
Adv rtr: 1.1.1.1 notice who RID
Ls Age: 532 times the normal aging period 1800 refresh, refresh trigger update causes; maximum aging 3609
len: 60 length
options: E options
seq #: 80000003 SEQ ID NO
chksum: 0xb2ee checksum code
The OSPF LSA 1800 will be updated once the next update will add a serial number.
Comparison of old and new LSA:
1, will first comparing the sequence numbers, the sequence number larger more excellent,
2, if the same sequence number, compares the check value (Checksum) bigger and more preferably
3, if the check values are the same, it would be more LSA Age time, time is equal to mAX-age (3600)
4, if the time is not equal age max-age time, compares their difference, if the difference is 15 minutes (900 seconds), preferably a small
5, if the time is not age equal to max-age time, compares their difference, if the difference is less than 15 minutes, indicating that the LSA is the same, wherein a is ignored.
Under what circumstances would LSA update:
1,1800 maturity will be updated
2, trigger an update (interface address change (increase or delete), change the interface cost value, delete interface, or delete announcements)
[r4-ospf-1] Import- route rip 1 RIP process 1 to redistribute the OSPF process 1
[r5] Run the display ospf router to view the LSDB ASE originate-5 class LSA
ASBR- autonomous system boundary router - routers border agreement
LSA-specific information:
Three optimizing OSPF protocol, to reduce the amount of the LSA updates:
normal class. 1 is a device an LSA, LSA class 2 is a network of a DR; class 3 and class 5 is a route one LSA; ASBR. 4 is a class . produces a
1. summary ---- reduce the amount of update of the backbone;
- Summary interdomain routing - the region of non-aggregated backbone to backbone area
configured on the ABR
[R1] OSPF. 1 [
R1--OSPF. 1] Area 2 only summary route generated by the local region class 2 the LSA
[R1- ospf-1-area-0.0.0.2] abr-summary 5.5.4.0 255.255.252.0
NOTE: after the summary configuration, empty interface need to manually add the anti-loop
2) outside route summarization: re-routing as published introduced from outside the ASBR; it be introduced on the ASBR
[R4] OSPF. 1
[R4--OSPF. 1] ASBR-Summary 99.1.0.0 255.255.252.0
2. Special areas:
special areas - reducing non-backbone area update amount - can not be backbone area, a virtual link can not exist;
1) can not exist ASBR:
"1" peripheral area stub refuse 4/5 class of LSA; generating a 3 default routing directed backbone area
[R5] OSPF. 1
[-OSPF-R5. 1] area 2
[R5-OSPF-0.0.0.2. 1-area-] Stub
Important: All devices are required in the region defined as the peripheral region;
" 2 "fully distal tip region based on the area, a further 3 LSA rejected, leaving only a default class 3;
configure the peripheral region, and the region can be fully defined only in the ABR;
[R1-OSPF area-0.0.0.2--1] Summary Stub-NO
2) presence ASBR:
"1" NSSA incomplete distal region - the region refuse 4 / 5LSA ASBR other regions generated; 5 LSA ASBR art produced in the region, in this class of diffusion region 7, from entering the backbone area of the region converted by the ABR (new ASBR) into 5; 7 and automatically generate a default directed backbone area;
[R4] OSPF [OSPF--R4. 1] 1 are
[r4-ospf-1-Area-0.0.0.1] all the equipment required to configure the nssa the region
"2" totally NSSA - in NSSA Basis, further rejection of the LSA 3; 3 generates a default class directed backbone area; the first region configured as an NSSA area, and then only in the defined ABR completely to
[r3-ospf-1-area -0.0.0.1] nssa no-summary
Important: After considering the network connection to the ISP, and the default generated OSPF default route may cause special region generating a loop;
which region is connected to the ISP, then the region can not be set to any particular region;
