Network equipment hard core technology insider router Chapter 13 from deer by device to router (Part 1)

today , Let's go back to our original heart , Start with the debate between router and deer by device in the preface .

see , This guy is ( Yes 6 A horned one ) Deer's organ ！

Yes , Home Internet , Household wireless devices are essential . that , Who knows , From home wireless devices to Internet Need to go through anything ？

First of all, this guy .

This thing is commonly known as “ Naked cat ”, It's actually Ethernet to EPON/GPON The bridge of , Formal address ONU.

EPON/GPON It is a kind of passive optical network , The means of connecting multiple terminals to an Ethernet interface . It is essentially a cheap half duplex light Hub, However, it has occupied the mainstream market of home broadband access of operators at its price .

The local end equipment of Guangmao is called OLT, One end of it is connected with multiple PON Optical fiber , It is distributed to multiple terminals through the beam splitter , The other end is via Ethernet , Connect to convergence and Metro edge devices .

Metro edge equipment has the ability to provide services for enterprises SR And providing services for home broadband BRAS.（ Now it's two in one ）SR Our business is not complicated , With QoS Mainly , and BRAS It is necessary to provide PPPoE And IPoE Two kinds of access , That is, from deer by device to router .

Insert ：BRAS It should read Bee-Ras. Never read as Bra-s. So the meaning changes .

The first contradiction that needs to be solved from deer by device to router is , Home broadband needs to be charged , And if there is no appropriate means of isolation , There is no way to avoid users without authentication , Communicate with Wang Gong next door through corridor switch , And connect to Internet.

The solution is simple ： Divide Zhang Jia and Lao Wang next door into two different VLAN No, that's fine ？

however , We need to know , Each station BRAS Number of users supported , Is far more than VLAN In quantity . With BRAS The best in the equipment ——H3C SR88-X For example , The number of users supported by the whole machine can reach hundreds of thousands .

therefore , Engineers thought of using a V** Technology to achieve per user isolation ——QinQ.

QinQ It was first used for the special line on the second floor of the metropolitan area , but VPLS/VLL Fade out of the special line circle after being born . It is the source of Ethernet MAC after , Add two layers 802.1q(VLAN TAG) Realized . As shown in the figure ：

Zhangjia and Wang are accessing the switch ( or OLT) The upper isolation is two VLAN, On the convergence switch , It is not simply to VLAN Trunk The mode is transmitted to the metropolitan edge router , But add a layer 802.1q label (VLAN TAG).

In order to realize authentication and billing , Operators generally use PPP As a means of Authentication . This kind runs on the Ethernet PPP, be called PPPoE(PPP Over Ethernet). Ordinary deer are made of utensils ( Home router ) They all support this function .

stay BRAS On , The tasks to be handled are ：

1. Remove two layers VLAN Tag;
2. Handle PPP State machine ;
3. about PPP The data packet , dismantle PPP head , Conduct IP Three layer forwarding ;

therefore , Such a complicated action , Utilization based on NP The implementation of the forwarding plane is a general practice .

In home broadband , There is also an important business , yes IPTV Business . We know , Whether TV or set-top box , There is no way to enter user name and password . For such users , How can we make it in BRAS On the Internet ？

Please look at the next breakdown .

Current issues ：

QinQ The network can be isolated as 4K * 4K = 16M Subnet , and VXLAN Also support 16M Subnet . that , Why not use VXLAN Isolate each user , And you want to use QinQ？

Last question ：

Why? LEM The table may not need to be in TCAM Storage in ？

answer ： because LEM Query key value of table (Key) It's a certain value , You can use hash tables (Hash Table) Organizing data structures . actually , In the switch ,MAC surface /MPLS By default, label tables are organized in this way , such ,LEM Can use relatively low cost SRAM Deposit , There is no need to consume high cost TCAM resources .