Route and Special IP address explanation

Route print:

Active routes:
Networkdestination netmask Gateway Interface Metric
1, 0.0.0.0 0.0.0.0 192.168.123.254 192.168.123.88 1
2, 0.0.0.0 0.0.0.0 192.168.123.254 192.168.123.68 1
3, 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
4, 192.168.123.0 255.255.255.0 192.168.123.68 192.168.123.68 1
5, 192.168.123.0 255.255.255.0 192.168.123.88 192.168.123.88 1
6, 192.168.123.68 255.255.255.255 127.0.0.1 127.0.0.1 1
7, 192.168.123.88 255.255.255.255 127.0.0.1 127.0.0.1 1
8, 192.168.123.255 255.255.255.255 192.168.123.68 192.168.123.68 1
9, 192.168.123.255 255.255.255.255 192.168.123.88 192.168.123.88 1
10,224.0 .0.0 224.0.0.0 192.168.123.68 192.168.123.68 1
11,224.0 .0.0 224.0.0.0 192.168.123.88 192.168.123.88 1
12,255.255 .255.255 255.255.255.255 192.168.123.68 192.168.123.68 1
, DefaultGateway: 192.168.123.254 -------------------------------------------------------

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========================================================== ====================================
Current route:
Destination network segment of destination
Mask Subnet Mask
The egress IP address of the router to which the interface reaches the destination.
The IP address of the next hop router entry of the Gateway. The router defines a link to the next router through the interface and gateway.

Normally, the interface and gateway are in the same network segment.
The number of metric hops. The quality of this route record. Generally, if there are multiple route records that reach the same destination, the router will

Use the route with a small metric Value
Article 1
Default route: when the destination CIDR block of a data packet is not in your route record

Where to send! The gateway of the default route is determined by the DefaultGateway on your connection.
This route record means that when the destination CIDR block of a packet that I receive is not in my route record, I will

192.168.123.88 this interface is sent to the address 192.168.123.254, which is an interface of the next vro.

The data packet can be delivered to the next vro for processing. It has nothing to do with me. Line quality 1 of this route record
Article 2
Default route:
This route record means that when the destination CIDR block of a packet that I receive is not in my route record, I will

192.168.123.68 this interface is sent to the address 192.168.123.254, which is an interface of the next vro.

The data packet can be delivered to the next vro for processing. It has nothing to do with me. Line quality 1 of this route record
Article 3
Local Loop: all the addresses in the network segment 127.0.0.0 point to their own machines. If such data is received, where should the route be sent?

Recorded line quality 1

Article 4
Route record of the direct connection CIDR Block: What to do when the router receives a packet sent to the direct connection CIDR Block? In this case, the interface of the route record

It is the same as gateway.
When I receive a packet whose destination CIDR block is 192.168.123.0, I will send the packet directly through the interface 192.168.123.68.

Because the port is directly connected to the network segment 192.168.123.0, the line quality of the route record is 1.

Article 5
Route record of the direct network segment
When I receive a packet whose destination CIDR block is 192.168.123.0, I will send the packet directly through the interface 192.168.123.88.

Because the port is directly connected to the network segment 192.168.123.0, the line quality of the route record is 1.

Article 6
Local Host Routing: How does a router handle a packet sent to itself?
When I receive a packet whose destination CIDR block is 192.168.123.68, I will accept the packet because it is sent to me

Your own, the route record line quality 1

Article 7
Local Host Routing: How does a router handle a packet sent to itself?
When I receive a packet whose destination CIDR block is 192.168.123.88, I will accept the packet because it is sent to me

Your own, the route record line quality 1
Article 8
Local broadcast route: What to do when the router receives the local broadcast sent to the direct network segment?
When I receive a broadcast packet whose destination CIDR block is 192.168.123.255, I will broadcast the data from the 192.168.123.68 interface.

Sent out. The route record's line quality is 1.
Article 9
Local broadcast route: What to do when the router receives the local broadcast sent to the direct network segment?
When I receive a broadcast packet whose destination CIDR block is 192.168.123.255, I will broadcast the data from the 192.168.123.88 interface.

Sent out. The route record's line quality is 1.
Article 10
Multicast Route: What to do when a vro receives a multicast packet
When I receive a multicast packet, I will send the data from the 192.168.123.68 interface in the multicast situation, the route record line

Quality 1
11th
Multicast Route: What to do when a vro receives a multicast packet
When I receive a multicast packet, I will send the data from the 192.168.123.88 interface in the multicast situation, the route record line

Quality 1
12th
Broadcast route: What should I do when the router receives an absolute broadcast?
When I receive an absolute broadcast packet, this packet is discarded.

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Special IP addresses that must be known

Just as each of us has an ID card number, each computer on the Network (more specifically, the network interface of each device) has

An IP address is used to identify itself. We may all know that these addresses are composed of four bytes, expressed in dotted decimal notation and Their A, B,

C classification, etc. However, in the total number of around more than 4 billion available IP addresses, Do you know some of the following common addresses with special meanings? Let me

Let me tell you!

I. 0.0.0.0

Strictly speaking, 0.0.0.0 is no longer a real IP address. It indicates a set of unknown hosts.

And target network. The "unclear" here means that no specific entries in the local route table indicate how to arrive. For the local machine, it is"

All "Three none" people you don't know will be sent to the shelter. If you set the default gateway in network settings

A default route with the destination address 0.0.0.0 is automatically generated.

Ii. 255.255.255.255

Restrict the broadcast address. For the local machine, this address refers to all hosts in the same broadcast domain in this segment. If translated into human languages,

It should be like this: "Everyone in this room has noticed it! "This address cannot be forwarded by the router.

Iii. 127.0.0.1

Local Address, mainly used for testing. In Chinese, it is "Myself ". In Windows, this address has a few

Name: "localhost ". Addressing such an address cannot send it to network interfaces. Unless an error occurs, it should never be in the transmission media.

The packet whose destination address is 127.0.0.1 appears.

Iv. 224.0.0.1

Pay attention to the differences between multicast addresses and broadcasts. From 224.0.0.0 to 239.255.255.255. 224.0.0.1 all

Host, 224.0.0.2 refers to all routers. Such an address is mostly used for some specific programs and multimedia programs. If your host is enabled

With the IRDP (Internet routing discovery Protocol, using the multicast function) function, your host routing table should have such a route.

V. 169.254.x.x

If your host uses the DHCP function to automatically obtain an IP address, when your DHCP server fails or the response time is too long

The wingdows system will allocate such an address for you beyond the time specified by the system. If you find that your host IP address is

Unfortunately, your network cannot run normally.

6. 10. x, 172.16.x.x ~ 172.31.x.x, 192.168.x.x

Private addresses, which are widely used in enterprise internal networks. Some broadband routers often use 192.168.1.1 as the default

Address. The private network may use random IP addresses because it is not interconnected with external networks. This address is reserved for use to avoid future accesses.

The IP address is messy when you enter the public network. When you connect a private network with a private address to the Internet, you must use address translation (NAT)

Translate it into a public legal address. This type of address cannot appear on the Internet.

For a host on a network, there are three valid destination network addresses that can be normally received: the local IP address, the broadcast address, and

Multicast address.

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Multicast, Multicast

I. Data Transmission over an IP Network
Multicast technology is one of the three methods of data transmission over an IP network. Before introducing the IP multicast technology, we first

And broadcast method to make a brief introduction:

Unicast transmission: Implements point-to-point network connection between the sender and each receiver. If a sender sends messages to multiple recipients at the same time

To transmit the same data, you must also copy multiple identical data packets. If a large number of hosts want to obtain the same copy of data packets

, Will lead to a heavy burden on the sender, long delay, network congestion; to ensure a certain quality of service needs to increase hardware and bandwidth.

Multicast Transmission: Implements point-to-point network connection between the sender and each receiver. If a sender sends multiple

The receiver only needs to copy the same data packet to transmit the same data. It improves data transmission efficiency. Reduces network congestion.

.

Broadcast Transmission: broadcasts packets in the IP subnet. All hosts in the subnet will receive these packets. Broadcast

The network delivers a packet to each host in the subnet, whether or not these hosts are willing to receive the packet. So the broadcast Scope

It is very small and only valid within the local subnet. Broadcast Transmission is controlled through the vro and vswitch network devices.

Ii. Multicast Technology
1. Architecture of IP multicast technology
The multicast protocol is divided into the group membership protocol between the host-router and the multicast routing protocol between the router-router. Group Member Association

This includes the IGMP (Internet Group Management Protocol ). Multicast Routing Protocols are classified into intra-domain multicast routing protocols and Inter-Domain multicast routing protocols. Intra-domain Multicast Routing

Protocols include PIM-Sm, Pim-DM, and dvmrp. Inter-Domain multicast routing protocols include mbgp and msdp. Meanwhile, to effectively suppress Multicast

Data diffusion at the link layer introduces igmpsnooping, cGMP, and other layer-2 multicast protocols.
IGMP establishes and maintains group membership information for the vro CIDR block. The intra-domain multicast routing protocol is composed of these multicast protocols maintained by IGMP.

User relationship information, using a certain multicast routing algorithm to construct a multicast distribution tree for multicast packet forwarding. Inter-Domain Multicast Routing Protocol in each autonomous domain

Route information with multicast capability and multicast source information are published between regions to forward multicast data between domains.

2. multicast IP Address
A Multicast IP address is used to identify an IP multicast group. Iana allocates Class D address space to IP multicast, which ranges from 224.0.0.0

239.00000000255. As shown in (binary representation), the first four digits of the IP multicast address are both 1110.
Octal group (1) octal group (2) octal group (3) octal group (4)
1110 XXXX XXXXXXXX

3. Group member protocol (IGMP)
The IGMP protocol runs between the host and the multicast router directly connected to the host. The host uses this Protocol to tell the local router to join and

Accepts information about a specific multicast group, and the router periodically queries whether a member of a known group in the LAN is active through this protocol.

Status (that is, whether the CIDR block still belongs to a multicast group) to collect and maintain the group members of the connected network.
IGMP has three versions. igmpv1 is defined by rfc1112. Currently, igmpv2 is commonly used and is defined by rfc2236. IGMPv3 is still one

Draft. Igmpv1 defines the basic process of querying and reporting group members. igmpv2 adds a mechanism for members to leave quickly,

The main function added in IGMPv3 is that a member can specify to receive or not to receive packets from some multicast sources. This section focuses on

Function.
Igmpv2 uses the queryer election mechanism as the only queryer for the connected CIDR Block election. The queryer periodically sends a universal group query message

Personnel relationship query; The host sends a report message to respond to the query. When you want to join a multicast group, the host does not have to wait for the query message to actively send a report

. When you want to leave a multicast group, the host sends an exit group message. After receiving the exit group message, the queryer sends a specific group query message to determine whether or not

All group members have left.
Through the above IGMP mechanism, a table is created in the multicast router, which contains the vro ports and the corresponding sub-Ports

Which groups of members are available on the Internet. When a vro receives a data packet from a group of G, it only forwards the data packet to the ports with G members.

. The routing protocol determines how data packets are forwarded between routers. The IGMP protocol is not responsible.

4. layer-2 multicast protocols
Layer-2 multicast protocols include IGMP snooping, igmpproxy, and cGMP.
The implementation mechanism of igmpsnooping is as follows: the switch forms a group member by listening to IGMP members from the host to report messages to the vro.

The relationship between the vswitch interface and the vswitch interface. Based on this relationship, the vswitch transfers the multicast packet received only to interfaces with group members.
IGMP proxy and IGMP snooping have the same functions but different mechanisms: igmpsnooping is only obtained by listening for IGMP messages.

Igmpproxy intercepts the IGMP request of the end user and then forwards it to the upper-layer router.
CGMP (Cisco group managementprotocol) is a private protocol developed by Cisco Based on the client/server model.

The multicast router can notify the vswitch when the host is added to or out of the multicast group based on the received IGMP packet.

The forwarding table constructed by this information is used to determine the interfaces to which multicast packets are forwarded. Gmrp is the standard protocol from a host to an Ethernet switch.

Enables multicast users to register multicast members on the second-layer switch.

5. Multicast Routing Protocol (PIM-SM)
Among the many multicast routing protocols, the most widely used protocol is PIM-SM Sparse Mode protocol-Independent Multicast.
In the PIM-SM domain, the router that runs the PIM-SM protocol periodically sends HELLO messages to find the adjacent PIM router, and

It is responsible for election of a specified router (DR) in a multi-channel access network. Here, Dr is responsible for distributing the root node to multicast for its direct connection group members.

Send a "Add/trim" message to or send the data from the direct connection multicast source to the multicast distribution tree.

Addressing
Class A 0.0.0.0-127.255.255.255
Class B 128.0.0.0-191.255.255.255
Class C: 192.0.0.0-223.255.255.255
Class D 224.0.0.0-239.255.255.255
A, B, and C class IP packet forwarding are based on the destination IP address. Class D (multicast address) packet forwarding is based on the source address.

Classification of multicast addresses:
Retain -- 224.0.0.0-224.0.0.255
User Group broadcast address -- 224.0.1.0-238.255.255.255
Local Management Group -- 239.0.0.0-239.255.255.255 (for private multicast domains, similar to private IP addresses)

RPF:
A multicast packet already ed on an interface will be accepted ifreceived on the interface that

Wocould be used to send a unicast IP packet back to thesource; this is called reverse path

Forwarding (RPF ).

Reverse route forwarding:
After the device receives a multicast packet on the interface, if the unicast route to the multicast source is also learned from this interface, the multicast data will be forwarded; otherwise, the multicast data will be lost.

Discard.