The MPLS WG Archive

[Shen Gangxiang <EGXShen@ntu.edu.sg>]

I think it is impossible as MPLS shim header is independent from IP header
except TTL field. I guess you may have something wrong during your
implementation.

Gangxiang

-----Original Message-----
From: Sung-eok Jeon [mailto:gte358s@prism.gatech.edu]
Sent: Friday, October 20, 2000 4:47 AM
To: mpls@UU.NET
Subject: Is IP TOS field changed by LSR? 


Dear Concerns,

How are you doing?

I and my friend are using the linux-mpls-ldp.pre7-0.200 

to setup a MPLS network supporting serveral service classes.

While we are trying to do setup our own network, 

we come upon a weird phenomenon. 

We think we observed that the TOS field of IP header is changed

from LSR to LSR. 

Is it really true that the TOS field is modified from LSR to LSR? 

If the above is true? what is the reason?  

(I guess the front part of IP header might be used as a Label field. 

 Is it right? )
 
-------------------------------------------------------------------------

The followings are what we are now trying to do :

   
1) Setup LSP( Source-LSR1-LSR2-Destination)

2) marking the TOS of IP header at LSR1.

   Because we want to support multiple services, we want to

   use the TOS field of the IP header.

3) Ping from source to destination and observe the packet content

   with Smartbit (between LSR1 and LSR2/ between LSR2 and destination).


==> Different TOS values according to different observing position.

-------------------------------------------------------------------------   

I hope some of you tell me if there is any mechanism modifying 

the TOS field of IP header in the program.

If ture, Is there any other new version which does not change the TOS field?


Thanks in advance.

Sung-eok Jeon