This series introduces the MPLS over GRE encapsulation (RFC 4023).
Various applications of MPLS make use of label stacks with multiple
entries. In some cases, it is possible to replace the top label of
the stack with an IP-based encapsulation, thereby, it is possible for
two LSRs that are adjacent on an LSP to be separated by an IP network,
even if that IP network does not provide MPLS.
An example of configuration:
node1 LER1 LER2
node2
+-----+ +------+ +------+
+-----+
| | | | | | |
|
| | | |p3 GRE tunnel p4| | |
|
| |p1 p2| +-------------------+ |p5 p6|
|
| +-------------+ +-------------------+ +------------+|
|
| |10.100.0.0/24| | | |10.200.0.0/24|
|
| |fd00:100::/64| | 10.125.0.0/24 | |fd00:200::/64|
|
| | | | fd00:125::/64 | | |
|
| | | | | | |
|
| | | | | | |
|
| | | | | | |
|
| | | | | | |
|
+-----+ +------+ +------+
+-----+
### node1 ###
ip link set p1 up
ip addr add 10.100.0.1/24 dev p1
### LER1 ###
ip link set p2 up
ip addr add 10.100.0.2/24 dev p2
ip link set p3 up
ip addr add 10.125.0.1/24 dev p3
modprobe mpls_router
sysctl -w net.mpls.conf.p2.input=1
sysctl -w net.mpls.conf.p3.input=1
sysctl -w net.mpls.platform_labels=1000
ip link add gre1 type gre ttl 64 local 10.125.0.1 remote 10.125.0.2 dev p3
ip link set dev gre1 up
ip -M route add 111 as 222 dev gre1
ip -M route add 555 as 666 via inet 10.100.0.1 dev p2
### LER2 ###
ip link set p5 up
ip addr add 10.200.0.2/24 dev p5
ip link set p4 up
ip addr add 10.125.0.2/24 dev p4
modprobe mpls_router
sysctl -w net.mpls.conf.p4.input=1
sysctl -w net.mpls.conf.p5.input=1
sysctl -w net.mpls.platform_labels=1000
ip link add gre1 type gre ttl 64 local 10.125.0.2 remote 10.125.0.1 dev p4
ip link set dev gre1 up
ip -M route add 444 as 555 dev gre1
ip -M route add 222 as 333 via inet 10.200.0.1 dev p5
### node2 ###
ip link set p6 up
ip addr add 10.200.0.1/24 dev p6
Now using this scapy to forge and send packets from the port p1 of node1:
p = Ether(src='de:ed:01:0c:41:09', dst='de:ed:01:2f:3b:ba')
p /= MPLS(s=1, ttl=64, label=111)/Raw(load='\xde')
sendp(p, iface="p1", count=20, inter=0.1)
