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

[Adrian P. <adr...@gm...>]

Hello Giuseppe,

You should be able to ping Host B (10.0.0.2) from Host A and viceversa. You
should not be able to ping 192.168.1.0/24 or other ip addresses because they
are not transported via MPLS. Just for standard ICMP traffic (64bytes
payload) the tunnel MTU should not be a restriction. Only for large packets
(1500 bytes) you should see packet drops at the tunnel ingress.

Cheers,
Adrian

On Thu, Jul 2, 2009 at 6:02 PM, Giuseppe Boncompagni <
giu...@gm...> wrote:

> 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
>
>
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