(1) P2P network
tlv240, the peer's system-id) is up when it receives its own system-id in the hello packet from the other party. The TLV240 contains: neighbor status, neighbor link ID, neighbor sys-id, and own link ID. On a P2P link, a neighbor relationship is established differently than a broadcast link. It is divided into a two-handshake and a three-way handshake mechanism. Two-way handshake mechanism:As soon as the router receives a hello packet from the peer, the router unilaterally declares the neighbor in the up state and establishes a neighbor relationship. Three-way handshake mechanism:In this mode, the ISIS Hello PDU that sends P2P three times finally establishes a neighbor relationship, which is similar to the establishment of a neighbor relationship for broadcasting. The two-way handshake mechanism is flawed. If there are two or more links between routers, if one link reaches the peer in the one-way state of down, and the other link reaches the same direction in the up state, the routers can still establish an adjacency relationship with each other. SPF uses the parameters on the link with the up state when calculating, which causes the router that has not detected the fault to try to pass through the link with the down state when the ** packet is packet. The three-way handshake mechanism solves the problems that exist in the unreliable point-to-point links described above. In this mode, the router declares that the neighboring router is up only when it knows that the neighboring router has also received the packets, thus establishing a neighbor relationship. (2) MA network(tlv6, the peer mac) when the hello packet sent by the other party has its own mac address, up
1.Rotera broadcasts Level-2LAN IIH without neighbor ID in this packet. 2.After receiving this packet, Router B identifies the neighbor status of the neighbor between Router and Routera as initial. The Router B then replies to the Router to the Level-2LAN IIH, which identifies Router as a neighbor of the Router B. 3.After receiving this packet, Routera indicates the status of its neighbor to RouterB as Up, and then Routerra sends a neighbor to RouterB that identifies RouterB as Level-2lan IIH. 4.After receiving this packet, Router B identifies its neighbor status with Routerra as Up. In this way, the two routers successfully establish a neighbor relationship. Because it is a broadcast network, it needs to elect a dish, so after the neighbor relationship is established, the router waits for the interval between the two hello packets before performing the DIS election. The hello packet contains the priority fieldThe one with the highest priority value will be elected as the DIS of that broadcast network. If the priority is the same, the MAC address of the interface with the larger MAC address is selected as the DIS.
2. Factors influencing the establishment of ISIS neighbor relations.
（1）levelLevel 1 cannot be a neighbor with Level 2（2）system-idIdentifies a router and is unique(3) CertificationType of Certification:Interface authentication: An interface that can authenticate Hello packets from Level 1 and Level 2 in a specified manner and password. Zone authentication: The region in which ISIS runs authenticates SNP and LSP packets at Level 1 in a specified manner and password. Router authentication: The routing domain running IS-IS authenticates SNP and LSP packets at Level 2 in a specified mode and password. Description:For zone and routing domain authentication, you can set SNP and LSP authentication separately. Locally-sent LSP packets and SNP packets carry authentication TLVs and perform authentication checks on received LSP packets and SNP packets. Locally sent LSP packets carry the authentication TLV and perform authentication checks on the received LSP packetsSNP packets are sent with an authenticated TLV, but the received SNP packets are not checked. Locally sent LSP packets carry the authentication TLV and perform authentication checks on the received LSP packetsSNP packets do not carry authentication TLV and do not perform authentication checks on received SNP packets. Locally-sent LSP packets and SNP packets carry authentication TLV, and do not perform authentication checks on received LSP packets and SNP packets. Authentication method:Plaintext authentication: A simple authentication method that directly adds the configured password to the packet, which is not secure enough for MD5 authentication: The security of the password is improved by adding the configured password to the packet after the MD5 algorithmKeychian authentication: The security of the network is further improved by configuring the password linked list that changes over time（4）mtuWhat is the difference between padding and p2p?By default, the MA of the MTU cannot be less than 1500, and the P2P cannot be less than 1497. The size of the neighbor MTU is known by the length of the PDU, all the hello packets in the MA network will be filled with padding, and the P2P will only be filled by the padding when the neighbor is established, and the other hello packets will not be filled. (5) Network interface typeThe network types on both P2P and MA are inconsistent, and neighbors cannot be established, and the required TLVs are different (TLV240 and TLV6). (6) For the same subnet, the mask can be inconsistentThe hello packet does not carry a mask, but carries an IP, and the router uses the received IP and the mask of the local interface to perform the calculation, which must be in the same network segment. (7) 3-way only caseA 2-way can make a neighbor with a 3-way, a 3-way and a 3-way only can make a neighbor, but a 2-way and a 3-way only can't make a neighbor (the 2-way doesn't carry TLV240). (8)cost-style(Affect route calculation, the difference between narrow and wide)1The cost value of the interface is 6 bits, so the value range is 0-64, and the cost length of the wide interface is 24, that is, the value range is 0 to 2, and the value is 24 minus 1. The metric for each route in type 135 is 32 bits long, so it is worth minus 1 to the power of 32 in the range of 0 to 2. 2.Wide supports sub-tlv and can be used to tag. 3.The TLV of different narrow is 2,128,130;The TLV of WIDE is 22,135. 3. ISIS messages - nine types.