OSPF Router-LSA Detailed
Frame relay environment DR and BDR election
. 1, DR and BDR in the same segment rather than the same area, because there may be a plurality of DR in the same area inside, a plurality of BDR; DR and BDR is a conceptual interface.
2, the NBMA network environment is generally not through multicast to establish neighbor relations, how to build relationships through neighbor multicast NBMA environment?
Need to network type to-multipoint, multicast packets will be sent from the interface group, you need to modify PVC:
We need to open the pseudo-broadcast:
After the open brocast, Frame Relay also supports multicast and broadcast
Add the broadcast keyword, change the network type, you can have a normal routing entries on R2, and algorithms are related.
Or the network type to point-:
Into a multipoint network type, DR and BDR election is not the only way through Unicast: point to point the way to maintain neighbor relationships.
Bar: The state machine is represented by the interface point (point to multipoint type network):
Multipoint, non-broadcast network (Frame Relay, ATM non-broadcast network environment, a low-speed link)
Network type hello timer dead timer DR / BDR election
Radio 1040 has
Non-broadcast networks have 30,120
No point 1040
No multipoint 30120
No no no virtual link
Non-multipoint broadcast (cisco) 30 120 No
Conclusion: Due to DR and BDR election will cause DR advertises class 2 LSA, resulting in SPF algorithm error, so just come out of a multipoint network type to solve this problem.
*******************************************************
OSPF LSA (LSA in OSPF which is one of the most important elements)
LSA: link state advertisement, LSA various different content advertised
LSDB: the link state database is stored in different types of LSA
After With LSA, you can perform SPF algorithm to calculate the shortest path
ASBR: The Rip, Eigrp redistributed into OSPF, then its role is ASBR
ASBR: Autonomous System Border Router (if some external routes redistributed into OSPF, such a device is ASBR)
ABR: Area Border Router, connected to the plurality of regions
Conventional OSPF LSA? (R / S)
类 1 LSA (Router LSA):
Who Notice
: All devices OSPF configuration;
Convey the scope of
: the region Newsletter
2 will not be passed Class 1 LSA 1 to 3, but can be transmitted in the region; eventually, all devices in the region of this class have 1 LSA
Content of Notice
: Notice all the declared information into the OSPF link
show ip ospf database // View LSDB
Router Link states:1类LSA
ADV Router: Advertising Router
Age: age of a time -LSA aging time; Maximum an LSA: 3600 seconds;
Seq # SEQ ID NO: 0X 80 00 00 02 4 bytes, 1 byte 8 bits, 264 bits 32 2
checksum: a check on the LSA
Link count: in this LSA inside, notice a few link information
show ip ospf database? // view a variety of LSA
Why router-id can not be repeated?
Because LSA advertised time, it identifies the LSA advertised by whom, and to identify who is their Router-id.
ip router ospf Database 12.1.1.1 Show
// add router parameters, see after a specified link-state ID, in fact, the Link State ID equal to its Router-ID
LSA head of content:
Class 1 LSA's contents:
R1#show ip ospf database router 12.1.1.1
OSPF Router with ID (12.1.1.1) (Process ID 1)
Router Link States (Area 0)
Age LS
: 331 \\ LSA save time, the aging time of 3600S, LSA update time for the 1800S.
Options: (No TOS-capability, DC)
LS Type: Router Links \\ 1类LSA
State ID Link
: \\ 12.1.1.1
Class 1 LSA LS ID in the sender is equal to Router-id
Router Advertising,
: \\ 12.1.1.1 LSA's advertised Router-id (filled LSA's advertised Router-id)
Seq Number The the LS
: \\ the LSA Serial No. 80,000,002 32 'bit, the first bit represents a symbol (1 = 0 = negative integer), while linear growth and lollipops algorithm used. Each LSA will update sequence number plus 1, so to represent each LSA is up to date
Checksum: 0xCF25
Length: 36
Number of Links: 1
Link connected to: a Transit Network link type -LINK type
(
Link ID) Designated Router address: 12.1.1.2
(
Link Data) Router Interface address: 12.1.1.1
Number of TOS metrics: 0 Type of Service
TOS 0 Metrics: 1
How to compare the old and new of a LSA? (General procedure)
1. LSU to announce LSA, LSA to determine whether the LSDB inside?
2. If so, compare the serial number to see the serial number are the same?
If consistent, Ignore LSA; if not, look at the LSA sequence number is greater than a locally saved? If so, the reception, replace the locally stored LSA; if not, continue to the LSA to my neighbors
3. If this is not the LSA LSDB inside, you need to put this added to the LSA LSDB, and send LSACK, to flood LSA, to neighbors, to do the follow-up to run the SPF algorithm to calculate a
Class 1 LSA in fact, to represent a 31bit serial number, serial number if it reaches the maximum, the minimum will repeat the sequence number, start re-execution algorithm, which is a lollipop algorithm
Growing method: linear growth
32-bit bit inside, which is representative of 31bit sequence number, the first one bit representative of the sign, a is negative, 0 is a positive number
The smallest sequence number hexadecimal: 0x80000001 = 1000 0000 (80)
-0000 0001
-ffff ffff
00000000
7f ff ff ff
OSPF growth requires the serial number of years spent 100
LSA sequence number uses two algorithms: (1) linear growth (2) Algorithm lollipop
checksum: make a hash of the LSA, LSA ensure reliability, tamper-proof
There are four types of links:
LINK type LINK-ID LINK-DATA
Transit DR Interface IP address Interface IP address
Poinit-to-point (P2P) neighbor Router-id this interface IP address
Stubnet network address prefix mask address
Virtul-link virtual link neighbor Router-id MIB interface ID (IP address of the interface)
// look inside the OSPF LSU packets
Do Not Age: If this bit is bit 1, the LSA never aging
Flags: routerLSA only contained in the inside, to know how the network is virtual links / ASBR / ABR - V / E / B
Note: contains three flag bits in the Router-LSA.
1, Vbit virtual link identifier
2, Ebit logo is ASBR
3, Bbit logo is ABR
How the serial number in OSPF LSA judgment of old and new?
(
And I need to make a comparison of the LSA after receiving a LSA, LSA with the new to replace the old LSA
)
1, comparing the sequence numbers, the greater the new sequence number.
2, if the same serial number, checksum comparison value, the greater the new.
3, if the checksum as compared LSA AGE, if LSA AGE equal to MAX AGE (3600) to date.
Description This LSA is needed immediately aged out of
4, if the LSA AGE is not equal to MAX AGE, need to run Maxage diff algorithm, LSA's LSA and saved locally comparing the received AGE time difference if the time difference is more than 15 minutes, LSA AGE smaller the new, is less than 15 minutes is considered to be same, ignored.
1.R4 forwarding delay is set to 500s, after 500 plus R2, R3 plus after 500s, turns 1000s
, Equal to about 16 minutes
R4 2.R3 time to more than 1000 s, R3 and R4 to about 2 seconds
3. Now LSA age> max age 15 minutes, R4 to R3 becomes the new LSA replace R3 to R4 of LSA
Class 2 LSA (Network LSA):
3类LSA（Network summary LSA）：
4类LSA（ASBR summary LSA）：
Class 5 LSA (AS External LSA): AS external LSA
Class 6 LSA: multicast LSA, for MSPF
7 Deliverable LSA (NSSA LSA):