Simple introduction to Intelligent DNS resolution + dual line access

Introduction : in the discussion of this issue, among the group of Friends of the old lone comrade also provides a lot of very valuable information, so we re-organize the data again, from the comparison of the underlying technical principles of a re-analysis. We know that because of the South telecom North Netcom phenomenon, our server or network content, services and other providers of network choice is also important. Each webmaster or network content, service providers want their own site in the country and even the world can be quickly accessed by users, but the reality of national conditions, single ... Text:

In fact, the implementation of the two-wire technology is not a new technical problem, White is Intelligent DNS resolution + dual-line access , but recently many friends are discussing this problem, among them group friends old Lone Comrade also provides a lot of very valuable information, so we re-organize this information again, Re-analyze the underlying technical principles.

We know that because of the South telecom North Netcom phenomenon, our server or network content, services and other providers of network choice is also important. Each webmaster or network content, service providers want their own site in the country and even the world can be quickly accessed by users, but in reality, a single server is difficult to achieve. Foreign network speed is slow, stationmaster and Netizen also can understand and accept, but domestic north and south of obstruction, believe stationmaster is difficult to understand also difficult to accept. But this is the case, the webmaster can only according to their own website mainstream user group is in the south or in the North, service focus is in the South or the north and make a choice, if the south to choose a telecommunications network, such as the north of the selection of Netcom network. Of course, who do not want their own website because of the speed and less of the other part of the users and visitors, are trying to solve the network bottleneck, hoping to realize the north-South fast interconnection.

At present, the bottleneck problem of telecom and netcom can be mainly caused by human factors, and only by increasing cost or using technology to remedy, some IDC providers put forward "dual line", intelligent domain name DNS and CDN scheme respectively. The "dual-line" solution also includes dual-line single-IP routing solutions and dual-line dual-IP solutions. The DNS scheme is based on the domain name of the network resolution (mainly by the Internet users use the DNS server to judge), CDN (Content Delivery Network) solution, that is, "contents publishing and Courier Networks", this is a comprehensive solution for content providers.

And the majority of domestic operators out of the two-line scheme is actually dual-line dual-IP scheme, only a few regions and a few operators have the means to achieve the BGP mode of two-line single IP.

Here by the way: what is BGP dual floss? What are the conditions for establishing a BGP double line?

First, BGP (Border Gateway Protocol Border Gateway Protocol) is mainly used for interconnection between internet as (autonomous system) and is a routing protocol for dynamically exchanging routing information between autonomous systems. The classic definition of an autonomous system is a set of routers under the control of an administrative agency that uses IGP and ordinary metrics to forward messages to other autonomous systems. BGP (Border Gateway Protocol) is an external gateway protocol that communicates between different autonomous system routers, as an EGP substitute, the reachable information of a switched network between BGP systems, which includes all the paths in the autonomous system as that the data must pass to reach these networks. Through this information constructs the autonomous System link diagram, then deletes the routing ring according to the connection diagram, formulates the routing strategy.

BGP two-wire implementation of the first two-wire network compared with the most important feature is that the server only need a network card, so there is no need to change on the client's server, but the operator needs to purchase a more expensive BGP router, so this two-wire technology is also known as "full routing two lines." The network of telecom and Netcom connects to the operator's BGP router, which is then assigned by the switch to each client's server. Because China Netcom and Chinese telecom both have as number (autonomous system number), the majority of the country's major network operators through the BGP protocol and its own as number to interconnect. Using this scheme to achieve dual-line needs in CNNIC (China Internet Information Center) to apply for IDC's own IP address segment and as number, and then through the BGP protocol to broadcast this IP address to Netcom, telecommunications and other network operators, After using BGP protocol interconnection, all backbone routing devices of netcom and Telecom will judge the best route of IP segment in IDC computer room to ensure high-speed access of Netcom and telecom users.

In fact, the current BGP dual-line (single-IP two-line) is mainly concentrated in Beijing and Shanghai, because Beijing is the network management department and the telecommunications sector base, so to do BGP is not difficult; Shanghai is the establishment of an ISP interconnection organization to mediate, thereby solving the BGP problem; but Guangdong is one of the largest telecommunications, And the department does not accept the BGP processing procedures, so although many IDC operators in South China have got the autonomous as domain, but still can only use the dual-IP dual-line.

Dual- Line dual-IP scheme

For example, the IDC computer room in Guangdong province, the dual-IP two-line scheme is to install a server on a two network cards, respectively, access to the telecom network cable and Netcom network cable and set up a netcom IP and a telecommunications IP, so that a server has two IP addresses, It is necessary to add the routing table of Netcom or telecom to the server to realize the access of Netcom users and telecom users from different lines respectively. Although the cost of this scheme is low, but the network is not stable and occupy a large number of server resources, and some low-end servers have only one NIC interface, is 1U, to expand a network card is more troublesome, to pass the card, but also to purchase an additional Gigabit network card.

The scheme appears early, and the technology is relatively mature, but there are some drawbacks, the first is to waste IP resources, in addition to the need for the server has two network interface card.

So how does this technique work? First of all, the client's browser will submit a domain name, the domain name of course is submitted to the user network connection use of the DNS server, but the user's DNS server is unresolved, it will ask it on a level of DNS server, always ask, ask this domain name specified NS server, OK, This NS server to determine whether the user's line is telecommunications or netcom, if it is telecommunications, will return to the server's telecommunications IP, if it is Netcom's natural return to the server's netcom IP, so the DNS server after such a series of complex queries, Finally get a user to access the fastest IP address returned to the client, and then the client's browser to send a request to this IP address, the two sides to establish a TCP dialogue, this is probably the two-wire dual-IP implementation process. AC qq2881064152

Simple introduction to Intelligent DNS resolution + dual line access