nshkmod is a Linux kernel module implementation of Network Service Header. internet draft is https://tools.ietf.org/html/draft-ietf-sfc-nsh-01.

• Ehternet over NSH over VXLAN-GPE.
• Ethernet over NSH over Ethernet (ETHER_TYPE 0x894F).
• nsh type interface: An nsh interface is an entry point to a path.
• SPI/SI, next-hop and transport mapping table in kernel space.
• packet encapsulation, decapsulation and tx/rx in kernel space.
• modified iproute2 package. You can configure the mapping via ip nsh command.

It is only tested on Ubuntu 14.04.3 trusty, kernel version 3.19.0-25-generic.

Note: this is absolutely experimental implementation.

compile and install nshkmod.ko

 % git clone https://github.com/upa/nshkmod.git
 % cd nshkmod
 % make		# DEBUG=yes for debug mode.
 % modprobe udp_tunnel
 % insmod ./nshkmod.ko

compile modified iproute2 package

 apt-get install libdb-dev flex bison xtables-addons-source
 cd nshkmod/iproute2-3.19.0
 ./configure
 make
 # then you can do ./ip/ip nsh
 # and make install to /sbin/ip if you want.

An entry point for a path is an nsh interface. When xmit a packet to an nsh interface, the packet is encapsulated into NSH headers (base and path (and context if needed) headers). NSH encapsulated packets go through look-up mapping table process. Look-up key of the table is service path index and service index, and values of entries are next hop IP address and encapsulation type or nsh interface.

Received NSH packets from VXLAN newtorks are also processed in the same manner. Outer headers up to VXLAN are removed, checking service path index and service index, and received to an appropriate nsh interface in accordance with the mapping table.

By abstracting NSH paths as pseudo interfaces that means struct net_device, existing Linux network stack and its various functions can be used for network service chaining (e.g, Linux bridge, openvswitch, openflow and IP routing, etc).

At first, create nsh interfaces.

 % ip link add name nsh0 type nsh
 % ifconfig nsh0
 nsh0      Link encap:Ethernet  HWaddr be:2b:81:fb:34:0d
           BROADCAST MULTICAST  MTU:1500  Metric:1
           RX packets:0 errors:0 dropped:0 overruns:0 frame:0
           TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0 
           RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)
 % ifconfig nsh0 up

Validate interface TX mapping by ip command. 'dev nshX none' means TX of this interface is not mapped to any service path.

 % ip nsh show dev
 dev nsh0 none
 %

Map TX to a service path. Then, transmitted packets through nsh0 interface are encapsulated in network service header with service path index 10 and service index 5. Interface TX mapping can also be specified when link creation and validated by ip -d link show.

 % ip nsh set dev nsh0 spi 10 si 5
 % ip nsh show dev
 dev nsh0 spi 10 si 5
 %
 % ip link add name nsh1 type nsh spi 11 si 4
 % ip nsh show dev
 dev nsh0 spi 10 si 5
 dev nsh1 spi 11 si 4
 %
 % ip -d link show dev nsh1
 12: nsh1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default
     link/ether 86:74:9b:0d:8e:63 brd ff:ff:ff:ff:ff:ff promiscuity 0
     nsh spi 11 si 4 addrgenmode eui64
 %

Next, add a mapping table entry for the path. Then, transmitted packets through nsh0 interface with network service header are encapsulated again in VXLAN-GPE and transmitted to a remote host 10.0.0.2. Moreover, Ethernet over NSH over Ethernet is supported (vlan is not supported). When NSH is encapsulated in Ethernet header, Ethertype is 0x894F. This number is assigned to Cisco vPath Network Service Header in IEEE Ethertype assignment, but used for NSH in the draft.

 % ip nsh add spi 10 si 5 encap vxlan remote 10.0.0.2 vni 10
 % ip nsh add spi 11 si 4 mdtype 2 encap ether dst 08:00:27:93:f2:a7 link eth2
 % ip nsh show
 spi 11 si 4 mdtype 2 encap ether dst 08:01:27:93:f2:a7 link eth2
 spi 10 si 5 mdtype 1 encap vxlan remote 10.0.0.2 vni 10
 %

By the way, mdtype and vni can be omitted. Default MD-type is 1 and vni is 0. Note that current implementation does not consider vxlan VNI value. To delete mapping table entries, use ip nsh del with only spi and si arguments.

Finaly, interface RX should also be mapped to an other path. Serive path is always unidirectional.

 % ip nsh add spi 12 si 4 dev nsh0
 % ip nsh show
 spi 12 si 4 mdtype 1 dev nsh0
 spi 11 si 4 mdtype 2 encap ether dst 08:01:27:93:f2:a7 link eth2
 spi 10 si 5 mdtype 1 remote 10.0.0.2 encap vxlan vni 10
 %

Then, NSH packets with spi 12 and si 4 from networks over VXLAN-GPE or Ethernet or intra-host are received by nsh0 interface after decapsulation.

This pull request for tcpdump enables to display NSH over VXLAN-GPE packets.

nshkmod supports interface destination for service paths. By using this, You can configure service paths in a host.

By changing bridge to other functions such as openvswitch or virtual machine, a service function is inserted to the path.

• ip nsh commands
  • ip link add name nsh0 type nsh
  • ip link add name nsh1 type nsh
  • ip link add name nsh2 type nsh
  • ip link add name nsh3 type nsh
  • ip nsh add spi 3 si 2 dev nsh1
  • ip nsh add spi 3 si 1 dev nsh3
  • ip nsh add spi 4 si 2 dev nsh2
  • ip nsh add spi 4 si 1 dev nsh0
  • ip nsh set dev nsh0 spi 3 si 2
  • ip nsh set dev nsh1 spi 4 si 1
  • ip nsh set dev nsh2 spi 3 si 1
  • ip nsh set dev nsh3 spi 4 si 2

• ip nsh commands at Host 1

  • ip link add name nsh0 type nsh
  • ip nsh set dev nsh0 spi 12 si 6
  • ip nsh add spi 12 si 6 remote HOST2 encap vxlan
  • ip nsh add spi 10 si 5 dev nsh0

• ip nsh commands at Host 2

  • ip link add name nsh0 type nsh
  • ip link add name nsh1 type nsh
  • ip nsh set dev nsh0 spi 10 si 5
  • ip nsh set dev nsh1 spi 12 si 5
  • ip nsh add spi 10 si 5 remote HOST1 encap vxlan
  • ip nsh add spi 12 si 6 dev nsh0
  • ip nsh add spi 12 si 5 remote HOST3 encap vxlan
  • ip nsh add spi 10 si 6 dev nsh1

• ip nsh commands at Host 3

  • ip link add name nsh0 type nsh
  • ip link set dev nsh0 spi 10 si 6
  • ip nsh add spi 10 si 6 remote HOST2 encap vxlan
  • ip nsh add spi 12 si 5 dev nsh0

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