How VXLAN works on Linux
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This document discusses how VXLAN works on Linux in 3 parts: (1) it explains the basic mechanism of VXLAN including packet encapsulation and ARP resolution, (2) it describes how OpenStack Neutron implements VXLAN using the OVS plugin and ML2 l2population driver, and (3) it discusses the Flannel implementation of VTEP using Linux kernel extensions and an etcd key-value store.
![How VXLAN works on Linux
Basic mechanism and
Application to OpenStack and Docker
]中井悦司 / Etsuji Nakai
Senior Solution Architect
and Cloud Evangelist
Red Hat K.K
v1.1 2015/07/09](https://image.slidesharecdn.com/vxlan20150629e-150630053004-lva1-app6891/85/How-VXLAN-works-on-Linux-1-320.jpg)
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How VXLAN works on Linux
- 1. How VXLAN works on Linux Basic mechanism and Application to OpenStack and Docker ]中井悦司 / Etsuji Nakai Senior Solution Architect and Cloud Evangelist Red Hat K.K v1.1 2015/07/09
- 2. 2 How VXLAN works on Linux $ who am i 中井悦司 / Etsuji Nakai – Twitter @enakai00 – Senior Solution Architect and Cloud Evangelist at Red Hat. – The author of some OpenStack books.
- 3. 3 How VXLAN works on Linux Contents VXLAN basics OpenStack Neutron OVS Plugin VTEP implementation with Flannel References
- 4. VXLAN basics
- 5. 5 How VXLAN works on Linux The objective of VXLAN Creating virtual L2 network over physical L3 network. VXLAN Switch VXLAN Switch VXLAN Switch Tokyo Osaka Fukuoka 10.1.0.0/16 10.1.1.0 10.1.2.0 10.1.3.0 Physical view Logical view from servers
- 6. 6 How VXLAN works on Linux Packet encapsulation with VXLAN header VXLAN encapsulates L2 packet inside L3 packet. VXLAN Switch VXLAN Switch Tokyo Osaka Dest Address yy.yy.yy.yy Original Packet Source Address xx.xx.xx.xx Original Packet VXLAN Header xx.xx.xx.xx yy.yy.yy.yy Original Packet
- 7. 7 How VXLAN works on Linux
- 8. 8 How VXLAN works on Linux The fundamental problem of L2 over L3 How to find the correct location of packet destination? How did you know that the destination is in Osaka!? VXLAN Switch VXLAN Switch Tokyo Osaka Dest Address yy.yy.yy.yy Original Packet Source Address xx.xx.xx.xx Original Packet VXLAN Header xx.xx.xx.xx yy.yy.yy.yy Original Packet
- 9. 9 How VXLAN works on Linux ARP resolution on L2 layer VXLAN switches need to emulate the ARP resolution mechanism. IP 10.1.2.0 MAC zz:zz:zz:zz:zz:zz ① ARP Request "What's the MAC for IP 10.1.2.0?" ② ARP Reply "zz:zz:zz:zz:zz:zz" Dest IP 10.1.2.0 Source IP 10.1.1.0 Payload Dest MAC zz:zz:zz:... Source MAC xx:xx:xx:... L3 headerL2 header IP 10.1.1.0 MAC xx:xx:xx:xx:xx:xx ④ Send L2 packet to "zz:zz:zz:zz:zz:zz" ③ Port <-> MAC association is recorded in MAC table
- 10. 10 How VXLAN works on Linux Additional features for L2 over L3 Packet encapsulation is not enough for L2 over L3. VXLAN switches need to implement the following features. – ARP resolution: Need to reply to ARP request from local servers without broadcasting the ARP packet. – Destination search : Need to find the destination location corresponding to the destination MAC. The VXLAN endpoint providing these features is referred as "VTEP". ARP Reply 「zz:zz:zz:zz:zz:zz」 Dest "zz:zz:zz:zz:zz:zz" is located in Osaka.VXLAN Switch Tokyo xx.xx.xx.xx ① ARP Request "What's the MAC for IP 10.1.2.0?" ④ Send L2 packet to "zz:zz:zz:zz:zz:zz"
- 11. 11 How VXLAN works on Linux
- 12. 12 How VXLAN works on Linux Variations of VTEP implementation To implement VTEP features, there must be some mechanism to share the tuple (MAC, IP Address, Location) of all servers. The followings are some variations of VTEP implementation. – Exchange MAC/IP information using L3 multicasting among switches. – Use SDN controller as a central MAC/IP database. – Use local agent and virtual VXLAN switch running on Linux servers.
- 13. OpenStack Neutron OVS Plugin
- 14. 14 How VXLAN works on Linux ML2 l2population driver In the case of OpenStack Neutron OVS plugin, VXLAN encapsulation is done on the local Open vSwitch on compute nodes. – MAC/IP information is sent by L2 agent and populated by l2population ML2 driver. – The l2population driver populates the following entries in OVS. • FDB (forwarding database): a lookup table to find a destination node corresponding to the dest MAC address. • Flowtable entries for replying to ARP requests from local VMs. VM OVS (br-int) VM l2population driver Messaging server （RabbitMQ） VM OVS (br-int) VM l2population driver L2 Agent L2 Agent ① Attaching new VM ② Send MAC/IP information ③ Populate flow table in OVS
- 15. 15 How VXLAN works on Linux Reference : ML2 – Address Population – http://assafmuller.com/2014/02/23/ml2-address-population/
- 17. 17 How VXLAN works on Linux Overlay network with Flannel Flannel is a opensource tool to create overlay network for Docker containers. It's often used with Kubernetes. – It uses Linux kernel's native VXLAN devices for packet encapsulation. – Flannel daemon dynamically populates FDB and ARP table according to the kernel requests via the "L2/L3 MISS" notification mechanism. • The mechanism is originally named as "DOVE extensions" • https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/? id=e4f67addf158f98f8197e08974966b18480dc751 – The IP/MAC information is shared with the backend KVS (etcd). etcd Physical network 192.168.122.0/24 Minion flannel.1 Minion flannel.1 Internal network for container communication 10.1.0.0/16 Minion flannel.1 VXLAN device
- 18. 18 How VXLAN works on Linux Kernel's DOVE extensions You can use the native VXLAN device with the current Linux kernel. – You don't necessarily need OVS for using VXLAN. – It's just like using the traditional VLAN device with Linux :) VTEP features are implemented with a userland agent via "L2/L3 MISS" notification mechanism. (The notification is sent via netlink.) – L3MISS • The kernel asks the agent to populate the local ARP table when necessary instead of broadcasting the ARP request packet. – L2MISS • The kernel asks the agent to populate FDB when necessary. # ip -d l show flannel.1 3: flannel.1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1450 qdisc noqueue state UNKNOWN mode DEFAULT link/ether 82:ce:d5:09:06:2c brd ff:ff:ff:ff:ff:ff promiscuity 0 vxlan id 1 local 192.168.122.101 dev eth0 srcport 0 0 dstport 8472 proxy l2miss ageing 300 # bridge fdb show dev flannel.1 56:e1:c1:d6:b7:51 dst 192.168.122.102 self # cat /proc/sys/net/ipv4/neigh/flannel.1/app_solicit 3
- 19. 19 How VXLAN works on Linux Reference: Kernel patch - add DOVE extensions for VXLAN – https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/? id=e4f67addf158f98f8197e08974966b18480dc751
- 20. References
- 21. 21 How VXLAN works on Linux References ML2 – Address Population – http://assafmuller.com/2014/02/23/ml2-address-population/ Kernel patch: add DOVE extensions for VXLAN – https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/? id=e4f67addf158f98f8197e08974966b18480dc751 FlannelのVXLANバックエンドの仕組み – http://enakai00.hatenablog.com/entry/2015/04/02/173739
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