[mpls-linux-general] mpls : mtu and tunnels

[Giuseppe B. <giu...@gm...>]

hi all, sorry for may english
i've got a problem with MPLS and tunnel
i try to make this experiment :

MPLS for Linux: IPv4 over MPLS: two LER example for mpls-linux-1.95x

                           172.16.0.0/24
10.0.0.1/32                      |                      10.0.0.2/32
  dummy0                       |                         dummy0
    |                                 |                           |
 --------eth1          eth1------eth2         eth2------eth3   eth3--------
| HOST A |-----------|    LER1 |-------------| LER2 |---------| HOST B |
 --------.1   ^               2------.2                3------.3   ^
    4--------
              |                                                               |
              |                                                               |
        192.168.0.0/24                                          192.168.1.0/24

Traffic from HOST A to HOST B
=============================

HOST A
------
ip route add 10.0.0.2/32 via 192.168.0.2 src 10.0.0.1

LER1
-----
mpls nhlfe add key 0 instructions push gen 1000 nexthop eth2 ipv4 172.16.0.3
(returns key 0x2)
ip route add 10.0.0.2/32 via 172.16.0.3 mpls 0x2
echo 1 > /proc/sys/net/ipv4/ip_forward

LER2
-----
mpls labelspace set dev eth2 labelspace 0
mpls ilm add label gen 1000 labelspace 0
mpls nhlfe add key 0 instructions nexthop eth3 ipv4 192.168.1.4
(returns key 0x2)
mpls xc add ilm_label gen 1000 ilm_labelspace 0 nhlfe_key 0x2

Traffic from HOST B to HOST A
=============================

HOST B
------
ip route add 10.0.0.1/32 via 192.168.1.3 src 10.0.0.2

LER2
-----
mpls nhlfe add key 0 instructions push gen 2000 nexthop eth2 ipv4 172.16.0.2
(returns key 0x3)
ip route add 10.0.0.1/32 via 172.16.0.2 mpls 0x3
echo 1 > /proc/sys/net/ipv4/ip_forward

LER1
-----
mpls labelspace set dev eth2 labelspace 0
mpls ilm add label gen 2000 labelspace 0
mpls nhlfe add key 0 instructions nexthop eth1 ipv4 192.168.0.1
(returns key 0x3)
mpls xc add ilm_label gen 2000 ilm_labelspace 0 nhlfe_key 0x3

NOTES
-----
Make sure the MTU of the link between LER1 and LER2 is 4 bytes greater then
the MTU of the links between HOST A/LER1 and HOST B/LER2.

Think about it, here is what a IPv4 packet going from HOST A to HOST B
looks like on the link from LER1 to LER2:

{ler2 mac|ler1 mac|0x8847|1000,0,1,255|IP payload}

Everything is ok, but if i make a tunnel from LER1 to LER2 i can't
ping host A and Host B
how can set MTU 4 bytes grater in link HOSTA/LER1 and HOST B/ler2 ?
is it possibile that it is the problem ?
thx a lot
Best regards
Giuseppe