The MPLS-OPS Archive

["Tarun Bhalla" <tarun.bhalla@wipro.com>]

hi Roger..

 

as I replied to Wulf.. I m not doing my tests on

any set of routers/switches rather they are some

set of Linux boxes with intermediate interfaces having

mtu as 1500 bytes.. so i guess i will have to apply

fragmentation and reassembly but am doubtful whether

to go for that or not.. as it shall reduce the performance

to an huge extent..

 

also, if there are any standards that address this problem

that will be just great..

 

Thanks & Regards
Tarun B
_________________________________________________
Tarun Bhalla
Wipro Technologies
26 Hosur Main Road,
Bommanahalli,
Bangalore- 560 068. India
Tel +91-80-5732293, Extn 3139 <http://www.wipro.com/>

 

 

----- Original Message -----

From: Roger Clark Williams

To: MPLS-ops Mailing List

Sent: Thursday, March 20, 2003 10:47 PM

Subject: Fwd: [MPLS-OPS]: MTU problems in EoMpls domain..

Tarun, your issue is one of the classic trip-wire situations for MPLS. Since an MPLS/Ethernet frame is bigger than a normal Ethernet frame without labels, that bigger frame can be seen by some systems as an error, and the frame either dropped or fragmented, just as you say.

You may have to specifically set the MTU size for both the routers and switches. Though the routers may be MPLS-aware, the LAN interfaces, ie. Ethernet, don't automatically deal with jumbo frames. An MPLS frame would be the 1500 bytes of Ethernet plus the label(s) at 4 bytes each. You have to tell the routers what to do. Router WAN interfaces work differently. It is my understanding that the new MPLS Ethertypes carried in WAN headers inform the interfaces that a jumbo packet may be following, and the WAN interfaces on MPLS-aware routers will then accept it. Many non-MPLS-aware switches will discard these jumbo frames unless you tell them explicitly to allow them.

Look over this set of router commands....

interface fastethernet 0/0

mpls ip

mpls mtu 1512

and this switch command....

set port 1/3 jumbo enable

as possible candidates that may help.

Roger Williams

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Subject: [MPLS-OPS]: MTU problems in EoMpls domain..
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hi all,
 
I am new to this mailing list. so hi to all.. now my problems :((
Actually, I am trying to handle the problem of fragmentation in
Ethernet over MPLS network.
 
This is the existing network topology...
 
LAN A -------> MPLS Domain ----------> LAN B
 
To implement EoMPLS, I am capturing the packet in Ingress of the MPLS domain
and trying to send this as a payload over the MPLS domain.. When I
am doing this the problem is that the frames which are 1500 bytes (normal
ethernet frames) can not be sent across this MPLS domain as the payld
of this domain can only be 1496 bytes... (4 bytes label gets added and leave
the matter when multiple labels are added).. So, I am stuck as i am not
able to send 1500 bytes frames..
 
These all things are being carried on test setups. So, I can not
have the liberty or leisure to use SONET interfaces as my core n/w
interfaces.. also am not sure what to do in order to make use of jumbo
ethernet frames... So, the only option left is to fragment the frames when i
capture the ethernet frames.. but for that i need ur advice..
 
I mean is there any standard methodology that says how to handle
fragmentation in ethernet layer cos I will have to anyway go to this
final resort.. or is there any other way arnd. ??
 
Thanks & Regards
Tarun B
_________________________________________________
Tarun Bhalla
Wipro Technologies
26 Hosur Main Road,
Bommanahalli,
Bangalore- 560 068. India
Tel +91-80-5732293, Extn 3139 <http://www.wipro.com/>
 
 

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