云中网络-TODO
Network in the cloud
Virtualization networkcard
Flowchart
The steps are shown in the graph below:
Virtual machine could open a char dev file called TUN/TAP.
After opening this file, a virtual network card driver will be seen on the physical machine.
This virtual network card will intercept network packets and send it through TCP/IP.
The virtual network card tap0 will send network packets.
Share access
Connect internally
Use the Linux command to create an ethernet bridge
brctl addbr br0
Connect two virtual network card to br0
Connect to the outside
Network bridging
Def: Virtual machine and physical machine will share the same IP address.
Within cloud, the virtual machines inside Linux also share the same address as physical machines.
Cons: When there is a large scale of machines, broadcast will be a problem because each virtualized machine needs to be broadcasted.
NAT
Def: Virtual machines will have different ip address as physical machines.
A DHCP server will be created for assigning ip addresses to virtual machines dynamically.
Separation access
Approach: create VLAN based on physical network card eth0
vconfig
Within the same machine, there is no connectivity between network bridges.
Across machines, as long as physical bridge support VLAN, there will be no connectivity between different VLANs.
Overlay network
Motivation
Limitation of VLAN: Only has 12 bits and a capacity of 4096.
Possible solutions
Modify the VLAN protocol.
Extend the protocol by adding an additional header.
Definition
Underlay network: Physical network
Overlay network: Virtual network implemented on top of underlay network.
Approaches
GRE - Generic Routing Encapsulation
Idea: It increases the number of VLAN ID by the way of tunnel.
Example
Limitation:
The number of tunnels
It does not support group cast.
VXLAN
Idea:
SDN
Use cases
Control and forward
OpenFlow and Openvswitch
SDN controller administrates the network by OpenFlow protocol.
Within the Openvswitch, there is a flow table which defines flow rules.
References
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