| MPLS(4) | NetBSD Kernel Interfaces Manual | MPLS(4) |
In an MPLS domain the assignment of a particular packet a particular Forward Equivalence Class is done just once, as the packet enters the network. The FEC to which the packet is assigned is encoded as a short fixed length value known as a “label”. When a packet is forwarded to the next hop, the label is sent along with it; that is, the packets are “labeled” before they are forwarded.
A router capable of receiving and forwarding MPLS frames is called “Label Switch Router” or LSR. Label scope is generally router-wide meaning that a certain label has a specific meaning only for a certain LSR.
Currently, NetBSD supports MPLS over Ethernet interfaces and GRE tunnels. For these kind of interfaces, a label is contained by a fixed sized “shim” that precedes any network layer headers, just after data link layer headers.
------------------------------------------- | | | | | | Label | Exp. | BoS | TTL | | 20 bits | 3 bits | 1 bit | 8 bits | | | | | | -------------------------------------------
net.mpls sysctl(8) tree:net.mpls.acceptnet.mpls.forwardingnet.mpls.ttlnet.mpls.inet_mapttlnet.mpls.inet6_mapttlnet.mpls.inet_map_precnet.mpls.inet6_map_precnet.mpls.icmp_respond
“Pure” MPLS routes can be created using AF_MPLS sa_family sockaddrs for destination and tag fields. Other protocols can be encapsulated using routes pointing to mpls pseudo-interfaces, and AF_MPLS sockaddrs for tags. Decapsulation can be made using values of reserved labels set in the tag field (see below). For more information about doing this using userland utilities see the EXAMPLES section of this manual page.
The netstat(1) and route(8) utilities should be used to manage routes from userland.
ldpd(8) should be used in order to automatically import, manage and distribute labels among LSRs in the same MPLS domain.
# ifconfig mpls0 create up # ifconfig mpls0 inet 192.168.0.1/32
# route add 10.0.0.0/8 -ifp mpls0 -tag 25 -inet 192.168.1.100
# route add -mpls 50 -tag 33 -inet 192.168.1.101
add host 50: gateway 192.168.1.101
# route -n get -mpls 50
route to: 50
destination: 50
gateway: 192.168.1.101
Tag: 33
local addr: 192.168.1.180
interface: sk0
flags: <UP,GATEWAY,HOST,DONE,STATIC>
recvpipe sendpipe ssthresh rtt,msec rttvar hopcount mtu expire
0 0 0 0 0 0 0 0
sockaddrs: <DST,GATEWAY,IFP,IFA,TAG>
# route add 10.0.0.0/8 -ifa 192.168.1.180 -ifp mpls0 -tag 25 -inet 192.168.1.100For the latter example, setting an IP address for the mpls0 interface is not necessary.
# route add -mpls 60 -tag 3 -inet 192.168.1.100
# route add 10/8 -ifa 192.168.1.200 -ifp mpls0 -tag 20,30,40 -inet 192.168.1.100For the above example, tag 20 will be inserted at Bottom of Stack, while tag 40 will be set into the outermost shim.
# route add -mpls 60 -tag 30,40,41 -inet 192.168.1.100
Multiprotocol Label Switching Architecture, RFC 3031.
MPLS Label Stack Encoding, RFC 3032.
Users must be aware that the MPLS forwarding domain is entirely separated from the inner (IP, IPv6 etc.) forwarding domain and once a packet is encapsulated in MPLS, the former forwarding is used. This could result in a different path for MPLS encapsulated packets than the original non-MPLS one.
IP or IPv6 forwarding is not necessary for MPLS forwarding. Your system may still forward IP or IPv6 packets encapsulated into MPLS if net.mpls.forwarding is set.
| June 29, 2010 | NetBSD 5.99 |