MPLS-Linux: A C repository from donaldsharp

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MPLS BASICS:

Multi Protocol Label Switching (MPLS) represents a simple technology, which is
today indispensable in network cores. MPLS protocol adds a 32-bit header
(Figure 1) between the second and the third network layer headers.
Within these 32 bits, 20 bits are reserved for the label, 3 bits for
the Traffic Class (TC) field, 1 bit for the Bottom of Stack (S) field
and the remaining 8 bits are reserved for the Time to Live (TTL) field.

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Label
| Label | Exp |S| TTL | Stack
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Entry

Label: Label Value, 20 bits
Exp: Experimental Use, 3 bits
S: Bottom of Stack, 1 bit
TTL: Time to Live, 8 bits

Figure 1

A traffic class carried by means of a MPLS packet is defined based on the TC field.
Definition of an S field enables assigning of several labels to the packets. In the
label grouping, only the lowest label, closest to the IP packet, has S bit set to 1.
All other labels in the label stack have S set to 0. TTL field is used just like a
TTL field of the IP packet.

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BUILDING:

MPLS can be built as a kernel module, or it can be built in a kernel.

To build MPLS first you need to run:

$ make menuconfig

and enable MPLS compiling from:

Network setup -> Networking options -> MPLS (Experimental)

If you're running Debian based system, nice HOW-TO on compiling and installing custom kernel
can be found here:

https://help.ubuntu.com/community/Kernel/Compile

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RUNNING:

To be able to run MPLS, you will need modified iproute2 programme which can be downloaded from:

https://github.com/i-maravic/iproute2

Creation of MPLS tunnel ingress points is done with:

# ip link add tunnel_name type mpls push 300 192.168.2.2

or with

# ip route add 1.2.3.4 mpls push 300 192.168.2.2

To get more comprehensive explanation use:

$ ip link add tunnel_name type mpls help

$ ip route help

In order to be able to receive MPLS packets, interface must be MPLS enabled. This is done with:

# ip link set eth0 mpls on

To be able to receve MPLS packets recursively mpls0 interface must be brought up!

To build MPLS tunnel cross connect and egress points use:

# ip -M route add 200 mpls swap 300 dev eth0 192.168.3.3

MPLS SNMP stats are located in:

/proc/net/mpls_stats

MPLS sysctl parameters are located in:

/proc/sys/net/mpls

MPLS fully supports net namespaces.

IP-MPLS multipath routes are suported

Reserved labels, except the RouterAlert label, are handled properly.

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TODO:
1. Firewall support
2. ICMPv6 message sending, when TTL is exceeded or packet can't be forwarded because of MTU,
from the inside of MPLS tunnel
3. MPLS multipath
3. Bridging support

donaldsharp/MPLS-Linux