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Beginner

EoMPLS Problem

Would like to seek your help to resolve one EoMPLS problem.

My EoMPLS topology is-

CE1[3640]---(FE)---PE1[7206VXR,NPE300]---(FE)---P1[3640]---(E1)---P2[7206VXR,NPE-G1]---PE2[7206VXR,NPE-G1]---(FE)---CE2[3640]

I had configure Ethernet over MPLS on subinterface between PE1 & PE2. P1 and P2 connected via E1 (Encap PPP). On LDP path, MTU is 1530. MPLS L2 VC is up, I can ping CE - CE upto ping size 1480 byte, but not able to transfer any file. In FTP session between CE-CE, can receive only file size upto 1024 byte. I had also try MTU 1560 on the LSP, but result is same.

If I use FastEthernet between P1 and P2, everything works fine with MTU 1530.

How to resolve the issue of the above topology?

Rgds.

Mesbah

20 REPLIES 20
Beginner

Re: EoMPLS Problem

HI Mate,

i had same issue in my network. well i dont know if this solution helps you or not. after you change the MTU restart the router.

please let me know how did it go ?

Regards

amit

Beginner

Re: EoMPLS Problem

Hi Amit,

Today i found that, if i use Windows Vista on both CE side, FTP working fine from both end.

Windows Vista in one side and Windows XP in other side - XP can FTP from Vista but Vista cannot FTP from XP. Vista doing some Auto Tuning. I had also change MTU (1400, 1360)for VPN and PPP in Windows XP, but no result. I think the issue is the packet segmentation.

Beginner

Re: EoMPLS Problem

Hi

well that tricky. if possible capture the traffic and see if the DF bit is on.

Contributor

Re: EoMPLS Problem

mesbah

Only thing what you have to do is create a route map in which you have to map the traffic and fragment it and bind it to the ethernet or incoming port.

access-list 101 permit ip any any

route-map JUMBO

match ip-address 101

set df 1

interface x/x

route-map JUMBO in

regards

shivlu

Highlighted
Beginner

Re: EoMPLS Problem

Hi Shivlu,

my friend. i dont think he should be doing this .This will set DF for all the packets . which make packet ineligible for fragmentation.

is there any particular reason why you are recommending this ?

amit

Re: EoMPLS Problem

Hi Mesbah,

First lets agree that your core needs to accommodate the extra bytes added for labels allover the LSP, secondly are you filtering ICMP any where within your path. By default PMTUD is operational on Windows platforms, this means that all outbound TCP traffic will have the DF bit set, but if you are not filtering ICMP any where along your path thus PMTUD should work with no problem. One thing to note, the difference between Vista and XP regarding this issue is that Vista has a feature called PMTUBHDetect (Black Hole Router Detect) enabled by default (it can be manually enabled on XP, and more over SP3 enables it by default).

http://support.microsoft.com/kb/925280

http://support.microsoft.com/kb/314053/en-us

http://download.microsoft.com/download/6/8/7/687484ed-8174-496d-8db9-f02b40c12982/Overview%20of%20Windows%20XP%20Service%20Pack%203.pdf

BR,

Mohammed Mahmoud.

Beginner

Re: EoMPLS Problem

Hi Mahmoud,

your solution is pretty close. When we set PMTUBHDitect and PMTUDiscovery in registry of XP. It is working only when we are using router as a CE. Inside the CE routers Windows XP are working with these registry settings. But when we are using direct PC with PE router it does not work.

PC----SW---PE---P-----PE----SW---PC

F.M.Rashed Amin

www.link3.net

Beginner

Re: EoMPLS Problem

Hi Mahmoud,

Thanks for your post reply. We had enable LDP, TE and L2 MPLS. All over the LSP we had set "MPLS MTU 1530". Can we use MSS on PE router to reduce the packet size?

BR,

Mesbah

Re: EoMPLS Problem

Hi Mesbah,

Actually manipulating the MPLS MTU allover the path should do the job for you, anyway please do check the attached document, i've tried to have a single document that covers all the MTU, TCP MSS, PMTUD stuff covered, it is still in progress but i believe it'll help you understand most of the story.

BR,

Mohammed Mahmoud.

Beginner

Re: EoMPLS Problem

Hi Mahmoud,

Thanks for your document.

We had change MPLS MTU 1546, 9192, 9196 allover the LSP.

PC----SW---PE---P-----PE----SW---PC

But no result.

FTP working in one way, FTP from both side is not working.

BR,

Mesbah

Re: EoMPLS Problem

Hi Mesbah,

You are very welcomed, can you please post your configuration.

BR,

Mohammed Mahmoud.

Beginner

Re: EoMPLS Problem

Hi Mahmoud,

Please check the attachment.

Document file contain Network topology and configuration of all the router.

BR,

Mesbah

Beginner

Re: EoMPLS Problem

try to add 'ip tcp adjust-mss 1460' in subinterface on each PE to see if it helps.

Or use DrTCP on PC to small MTU size.

Beginner

Re: EoMPLS Problem

Hi Kevin,

MSS value in subinterface on each PE does not help.

BR,

Mesbah

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