2022-06-25 advanced network engineering (XI) IS-IS synchronization process of three tables (neighbor table, routing table, link state database table), LSP, cSNP, psnp, LSP

Three big watches

IS-IS Deal with the OSPF There are also three big watches .

Neighborhood watch

<R3>display isis peer 

                          Peer information for ISIS(1)

  System Id     Interface          Circuit Id       State HoldTime Type     PRI
-------------------------------------------------------------------------------
R2              GE0/0/0            R3.01             Up   21s      L2       64 
R5              GE0/0/1            R5.02             Up   7s       L2       64 
R6              GE0/0/2            R3.03             Up   23s      L2       64 

Total Peer(s): 3

System Id： System of neighbor device ID

interface： Exit interface

circuit id： link ID, It is divided into 2 Part of it is made up of , The first part says DIS Router , The second part represents the DIS Which links .

state： Current neighbor status

holdtime： Failure time

type： Established level

PRI： Interface DIS Election priority

Routing table

<R3>display isis route 

                         Route information for ISIS(1)
                         -----------------------------

                        ISIS(1) Level-2 Forwarding Table
                        --------------------------------

IPV4 Destination     IntCost    ExtCost ExitInterface   NextHop         Flags
-------------------------------------------------------------------------------
10.1.0.0/24          20         NULL    GE0/0/0         10.1.1.2        A/-/-/-
15.1.0.0/24          30         NULL    GE0/0/1         20.1.1.5        A/-/-/-
                                        GE0/0/0         10.1.1.2       
20.1.0.0/24          20         NULL    GE0/0/1         20.1.1.5        A/-/-/-
30.1.0.0/24          10         NULL    GE0/0/2         Direct          D/-/L/-
10.1.1.0/24          10         NULL    GE0/0/0         Direct          D/-/L/-
20.1.1.0/24          10         NULL    GE0/0/1         Direct          D/-/L/-
     Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
                               U-Up/Down Bit Set

IPV4 Destination： Destination network address

IntCost： Internal expenses

ExtCost： External expenses

ExitInterface： Exit interface

NextHop： Next jump

Flags： Sign a ,D- Direct link routing  A- Add to unicast routing table （ Non backbone area routing , from level-1-2 Router announcement ）, L- adopt LSP Release （ Route in this area ）, S- There is IGP Shortcut, U-Up/Down Bit Set（ For anti ring ）

PS: About U-Up/Down Bit Set The logo indicates this lsp The route of is originally issued by another region / Penetrating ,level-1-2 The router will prohibit it from sending back to another area , Avoid parameter loops

Link state database table

<R3>display isis lsdb 

                        Database information for ISIS(1)
                        --------------------------------

                          Level-2 Link State Database

LSPID                 Seq Num      Checksum      Holdtime      Length  ATT/P/OL
-------------------------------------------------------------------------------
R2.00-00              0x0000001e   0xe9f6        1112          126     0/0/0   
R3.00-00*             0x00000018   0xeb07        487           128     0/0/0   
R3.01-00*             0x0000000f   0xadcb        487           55      0/0/0   
R3.03-00*             0x0000000f   0x1063        487           55      0/0/0   
R5.00-00              0x00000015   0xdce9        837           126     0/0/0   
R5.02-00              0x0000000f   0xd49e        837           55      0/0/0   
R6.00-00              0x00000011   0x7436        823           74      0/0/0   

Total LSP(s): 7
    *(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended), 
           ATT-Attached, P-Partition, OL-Overload

LSPID：LSP identification , It is divided into 3 part . The first 1 Part of the identification generated by the router . The first 2 Partial representation DIS Which links ,0 For non DIS. The first 3 Part indicates whether to slice , Range 00-FF. An asterisk indicates that it is generated locally .

Seq Num： Link status serial number , Every time there is a topology change, add 1. Same as OSPF

Checksum： The checksum .

Holdtime： Failure time . Maximum by default 1200 second , Update cycle 900 second .

Length ：PDU length , Unit byte .

ATT/P/OL： Sign a .ATT- from level-1-2 Routers produce , Explain that the originating router is connected to other areas , P- Support area repair OL- Insufficient memory overload , When overloaded , This article LSP Will not participate in routing calculation , It can be manually set to overload state .

Relevant command

Set overload

[R1-isis-1]set-overload

Set up ATT Always set （ stay level-1-2 Configuration on router ）

[R1-isis-1]attached-bit advertise always 

Set up ATT Never set （ stay level-1-2 Configuration on router ）

[R1-isis-1]attached-bit advertise never 

Set not to learn level-1-2 Router because ATT Set the default route issued （ stay level-1-2 Adjacent to the router level-1 Configuration on router ）

[R1-isis-1]attached-bit avoid-learning

View the specified entry information

<R3>display isis lsdb verbose 0000.0000.0006.00-00

                        Database information for ISIS(1)
                        --------------------------------

                          Level-2 Link State Database

LSPID                 Seq Num      Checksum      Holdtime      Length  ATT/P/OL
-------------------------------------------------------------------------------
0000.0000.0006.00-00  0x00000014   0x6e39        562           74      0/0/0   
 SOURCE       R6.00
 HOST NAME    R6
 NLPID        IPV4
 AREA ADDR    49.0002 
 INTF ADDR    30.1.0.6
 NBR  ID      R3.03              COST: 10        
 IP-Internal  30.1.0.0        255.255.255.0    COST: 10        

Total LSP(s): 1
    *(In TLV)-Leaking Route, *(By LSPID)-Self LSP, +-Self LSP(Extended), 
           ATT-Attached, P-Partition, OL-Overload

SOURCE： Source entry

HOST NAME： Equipment name

NLPID： Protocol type

AREA ADDR： Area number

INTF ADDR： Interface IP Address

NBR  ID： Neighbor identifier .DIS identifier

IP-Internal： Segment information

LSP

Link status message LSP Used to exchange link status information .

Remaining Lifetime : LSP Survival time , In seconds .

LSP ID: It's made up of three parts ,System ID、 Pseudo nodes ID and LSP Number after slicing .

Sequence Number: LSP The serial number of . The first one sent when the router starts LSP The serial number in the message is 1, In the future, when it is necessary to generate new LSP when , new LSP The serial number of is in the previous LSP Add 1. Higher serial numbers mean newer LSP.

Checksum ： LSP Checksum .

ATT（Attachment）： from Level-1-2 Routers produce , Used to indicate whether the originating router is connected to other areas . Although this flag bit also exists in Level-1 and Level-2 Of LSP in , But in fact, this field is only related to Level-1-2 Router originated L1 LSP of .

OL（LSDB Overload,1bit）： Overload flag bit . Set the overload flag bit LSP Although it will spread in the network , But it will not be used when calculating the route through the overloaded router . That is, after setting the overload bit on the router , Other routers are in progress SPF This router will not be considered in the calculation . When the router is out of memory , The system automatically sends LSP Set the overload flag bit in the message .

IS Type(2bit)： Generate LSP Type of router . Used to indicate that Level-1 still Level-2 Router （01 Express Level-1,11 Express Level-2）. 

Grab bag observation

1.PDU length ：126 byte

2. Time to live ：1198 second

3.LSP-ID：0000.0000.0005.00-00

4. Link status serial number ： 0x00000000f

5. The checksum ：0x09c3

6. Check the state ：good

7. Generate LSP Type of router ： All flags 0, Grade 2 Of LSP（3 Indicates a two-level system 11 That's the hierarchy 2）

8. Indicates the protocol type

9. Indicates the area number

10. Indicates the name of the generated router

11. Indicates the system that generated the router ID and DIS Entry number

12. Indicates that the interface information of the router is generated

13. Ben LSP Included network segment information

CSNP

CSNP Include this device LSDB All of the LSP Abstract , Routers interact CSNP To determine whether synchronization is needed LSDB.

On the broadcast network ,CSNP from DIS Send regularly （ The default sending cycle is 10 second ）.

On a point-to-point network ,CSNP Send only when the adjacency relationship is established for the first time .

Source ID： issue CSNP Packet router System ID.

Start LSP：CSNP The first in the message LSP Of ID value .

End LSP ID：CSNP The last one in the message LSP Of ID value . 

Grab bag observation

1.PUD length ：147 byte

2. The source route of this message system ID：0000.0000.0003

3. Link identifier of the source route ：00

4. first LSP ID value ：0000.0000.0000.00-00

5. the last one LSP ID value ：ffff.ffff.ffff.ff-ff

6. The source route contains LSP A list of

PSNP

PSNP Only partial LSP Summary information of （ And CSNP Different ）

When you find LSDB Out of sync （ After adding a new device ）,PSNP To ask neighbors to send new LSP. 

In a point-to-point network , When I received LSP when , Use PSNP Yes, I received LSP Confirm . 

Source ID： issue PSNP Packet router System ID.

Grab bag observation

1.PDU length ：99 byte

2. The source route of this message system ID：0000.0000.0007

3. Link identifier of the source route ：00

4. The source route contains LSP A list of

LSP The synchronization process of

1.R3 Send HELLO Then establish adjacency . Then send the local LSP.

2.DIS received R3 Of LSP Then add to LSDB in . Send again CSNP.

3.R3 received CSNP Then compare your own LSDB. Send again PSNP Request missing parts .

4.DIS received PSNP Later, this part LSP Send to R3.

PS： The synchronization process of point-to-point network is similar to that of broadcast network .