Shulou(Shulou.com)06/01 Report--

TCP/IP protocol

Communication services across physical paths provided by the data link layer / physical layer

The transport layer / network layer provides communication services across logical or virtual paths consisting of a series of data links

It is normal that there is no response, but this one does not respond, which is low because the layer 2 encapsulation cannot be found, or the application layer does not respond. There is no problem with layer 3 information routing, because it is a directly connected network segment, so Ethernet communication must know the MAC address of the other party, but by default, it does not know, then it needs a mechanism to query, that is, ARP.

Whether in the case of the same network segment or different network segment, if the media of layer 2 is Ethernet, then the MAC address information of the other party must be obtained. The same network segment is the MAC address of the destination address, and different network segments are the next hop in the routing table. In a special case, if proxy arp is enabled, it is also the destination address, but MAC is the next hop. This is also in the current IPV4 network, ARP is a very insecure protocol, because it is easy to implement *, as long as the MAC of the gateway is told by the wrong MAC to the devices of the current network, then the communication of the whole network will not be normal.

This paper introduces the working process of Ethernet layer 2 encapsulation in TCP/IP protocol. In fact, in addition to Ether Ⅱ encapsulation, layer 2 encapsulation also has many protocols such as PPP, FR and so on. Here, we should pay attention to introducing two commonly used protocols. PPP and FR,FR are not often used in practice, but they are still required test points in the RS exam. However, this paper mainly introduces the importance and working process of layer 2 encapsulation in the case of routing information. Prepare for different situations of subsequent dynamic routing protocols in the case of FR. PPP here mainly introduces their negotiation process and some features, and the rest is nothing. In fact, PPP is not mentioned at all in Volume 1, because Cisco encapsulates HDLC by default, unlike H3C and HW, which defaults to PPP.

Frame Relay: Frame relay: fast packet switching technology for transmitting and switching data units in a simplified way at the data link layer

This problem can easily occur in dynamic routing protocols, including OSPF, EIGRP, RIP, ISIS (it also needs to map CLNS addresses)

The metrics of different routing protocols are different. {RIP is measured by hop count} {EIGRP defaults to bandwidth and delay} {OSPF and ISIS both rely on link bandwidth}. It is always 0 for static routes.

Host route, main network route, default route

The so-called main network routes are classified according to A, B, C

In this way, when forwarding a packet, the router first matches the host route or subnet route, and then matches the default.

CEF will copy the information of RIB (routing information forwarding library) into the FIB table, and will maintain a layer 2 forwarding information table, adjacency table, which contains layer 2 encapsulated information. For example, Ethernet is the source destination MAC and protocol number, and FR is DLCI. When the subsequent packets are forwarded, they directly read the information in CEF's FIB and ADJ table and forward them directly, which is realized by hardware. Instead of traditional forwarding packets need to be done by CPU, and recursively look up the routing table.

Often we prefer to use static routing because it consumes less resources than dynamic routing, but it is inflexible and can not adapt to changes in the network.

Int is interface interface f is fastEthernet fast interface 0ram 1 is the first port in slot 0

S0Compay 1, write the whole Serial 0Uniplet1. 0 represents the first interface module. 1 represents the second interface on the first interface module.

Lookback interface is one of the most widely used virtual interfaces.

24 is the CIDR value. To put it simply, a CIDR value corresponds to a subnet mask, and then the network is segmented. / 24 corresponds to 255.255.255.0 192.168.0.0Accord 24 represents 192.168.0.0 to 192.168.0.255

192.168.0.0 IP 24 represents 192.168.0.0 to 192.168.0.255 there are 192.168.1.0 to 192.168.1.255 192.168.2.0 to 192.168.2.255 and so on. How did these 24 get 255.255.255.0 each 32-bit address (bit), divided into four segments, each segment 8 bits (1 byte). To put it simply, 24 represents 24 1s after going, that is, 11111111.1111111111111111111111.00000000 to convert this to decimal system is 255.255.255.0.

Classless support for VLMS (variable length subnet mask) and CIDR (supernet)

Routing protocols have the difference between Classless and classful:

1 、 classful:RIPV1,IGRP

2 、 classless:RIPV2,EIGRP,OSPF,ISIS,BGP

Routing protocols can be classified by distance vector and link state

The difference between vlanif interface and vlan port:

(1) vlan port: it is a physical port. Usually we configure access vlan 10 to make a physical interface belong to vlan 10.

(2) vlan if: interface vlan is a logical port. Usually, this interface address is used as the gateway for users under the vlan.

When there is a three-layer network between AC and AP, because CAPWAP is a broadcast message by default, after the address is obtained by AP, the AC cannot be found and registered. At this time, the most commonly used is to use option43 of DHCP to transfer the IP address of AC to AP while AP obtains the address, and then AP will use CAPWAP unicast message to discover AC, thus completing the online registration of AC and AP under the three-layer network. Of course, you can also use option15 to inform AC of its location with DNS information. For the configuration of option43, please refer to DHCP Option 43 configuration method.

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