AS per above topology,am not able to transfer files with MTU frame size above 1492 though the MTU configured on interface is 1500.The link between DS/PE---CR/PE is mpls enabled i have configured the MTU size to 1524 to carry extra labels of MPLS as recommended by cisco.
When i do extnded ping from DS/PE above MTU size of 1492 with even DF bit not set am not able to ping customer end (B),
AND also i tried with DF bit set am not able to recieve any notifications ICMP destination unreacheable messages.
The file transfer from customer B with packet size above 1492 are received by customer A but when the connection are initiated through customer A they are not.
Within an enterprise it works with larger MTU size when tried to ping from DS loopback to core loopback.How can i troubleshoot it is a problem through my end or from the ISP.
response will be appreciated
from your last updates on this thread we can say:
a smaller MTU limitation is present in the other ISP network.
The customer starting a ping with size 1493 bytes receives an ICMP unreachable need to fragment sourced by ISP/PE node that is the PE node connecting to customer's site B.
A possible explanation is that Customer SiteB is connected to ISP/PE using PPPoE that has an overhead of 8 bytes leading to a max MTU of 1492 bytes for user traffic.
>> The command mpls MTU 1524 AND another command MTU 1524
the two commands do two different things:
mtu 1524 allow every protocol to increase their MTU it allows for an IP packet of size 1508 for example.
mpls mtu 1524: allows for an increase of MTU of MPLS frames.
To be noted that the second command doesn't specify how many MPLS labels should be inside the MPLS frame.
if both commands are used together an IP packet of size 1508 can be carried inside an MPLS frame with a label stack of two labels in a single frame:
1508+4+4 = 1516 size of resulting MPLS frame.
if we add ip mtu 1500 IPv4 packets cannot be greater then 1500 bytes.
Hope to help