mpls-linux-general

[mpls-linux-general] tcpdump bug?

[Daniel G. C. <da...@on...>]

Hi, now I'm making a network with 6 MPLS-Linux routers and I have made two
different LSPs with 'mplsadm'. The net is working properly, and the routes
are ok. I make ping from one LER to the other LER, in order to have
different destinations to test the different LSPs and ping works properly.

And I am capturing the packets with Ethereal (tcpdump) and, in one LSP, the
packets in one and other way (ping request and reply) are MPLS, BUT in the
other LSP, seems that the packets are not MPLS they are all normal IP
packets.

In the LSP that packets are showed as MPLS packets, I can see the 'famous'
tcpdump-MPLS-Linux bug in the received packets (when I run Ethereal in the
LER).
However in the other LSP appear the bogus IP packets that receives the LER,
too, but the sendings are not MPLS and I don't know if it is because of the
bug or other problem.

The scenario is:

     -- 6 -- 4
   /         /   \
 2         /     8
   \       /     /
     -- 3 -- 7

There are connections between Realtek ethernet cards and 3Com ethernet
cards, I guess it isn't the problem because the ping arrives properly. I am
working with Linux Red Hat 7.1 with Linux-MPLS
installed over kernel 2.4.13, I connect the PCs with cross-connect cables
and I am using ethereal 0.8.19.

The MPLS and route configurations are similar in the two LSPs so I think it
isn't a routing problem, and I don't know if it is a MPLS bug or I have
failed. Can someone help me?

Other question, can someone tell me how MPLS fragments the packets in a MPLS
Tunnel, when because of the size of the label stack (there are too many
labels), the packet's size exceeds the MTU?. I guess that there will be
something that does it but I don't know how MPLS does because in an MPLS
network the LSRs are working as switches so they can't fragment packets (Is
this correct or I am wrong?)

Thanks,Dani.

Re: [mpls-linux-general] tcpdump bug?

[James R. L. <jl...@mi...>]

On Wed, Apr 24, 2002 at 11:06:30PM +0200, Daniel Gregorio Catalan wrote:
> Hi, now I'm making a network with 6 MPLS-Linux routers and I have made two
> different LSPs with 'mplsadm'. The net is working properly, and the routes
> are ok. I make ping from one LER to the other LER, in order to have
> different destinations to test the different LSPs and ping works properly.
> 
> And I am capturing the packets with Ethereal (tcpdump) and, in one LSP, the
> packets in one and other way (ping request and reply) are MPLS, BUT in the
> other LSP, seems that the packets are not MPLS they are all normal IP
> packets.
> 
> In the LSP that packets are showed as MPLS packets, I can see the 'famous'
> tcpdump-MPLS-Linux bug in the received packets (when I run Ethereal in the
> LER).
> However in the other LSP appear the bogus IP packets that receives the LER,
> too, but the sendings are not MPLS and I don't know if it is because of the
> bug or other problem.

Are you sure they are going via IP?  Turn off IP forwarding on one of the
LSRs (echo 0 > /proc/sys/net/ipv4/ip_forward).

On your LERs, what FECs are you binding to the LSPs?  What are the IPs on
the outgoing interfaces?

> Other question, can someone tell me how MPLS fragments the packets in a MPLS
> Tunnel, when because of the size of the label stack (there are too many
> labels), the packet's size exceeds the MTU?. I guess that there will be
> something that does it but I don't know how MPLS does because in an MPLS
> network the LSRs are working as switches so they can't fragment packets (Is
> this correct or I am wrong?)

MPLS doesn't fragment, it needs to present a minimized MTU to the IPv4 layer.
If the resulting packet is bigger then the outgoing interface it should be
dropped (this isn't in mpls-linux yet).

Jim

> 
> Thanks,Dani.
> 
> 
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-- 
James R. Leu