MTU Issues

Hello Dear's

Topology:

Its a Carrier Supporting Carrier Scenario.

A------DS/PE---CORE/P---ISP/PE--P---ISP/PE------B

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 interface on
which customer A is connected MTU is default to 1500.The link between
DS/PE---CR/PE is mpls enabled i have configured the MTU size to 1524 to
carry 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
Distribution loopback to core loopback.How can i troubleshoot it is a
problem through my end or from the ISP.

The link between core and ISP is back to back VRF connected via a layer 2
trunk.The ISP is creating a sub-interfaces on his 3800 router with
encapsulation and vlan number.AND on Core am creating a SVI with a same vlan
number and ip address within the subnet.

Each customer VRF for exampl:(Customer A) is associated with SVI virtual
interface on 6500(core)and traffic is passed to customer B.On SVI the MTU is
default to 1500.

BGP is routing protocol between CORE nd ISP.

ON 3800 router (ISP End)
int gig0/0
no shut
no ip add

int gig0/0.1
no shut
encapsulation dot1q 50
ip vrf forwarding XX
ip add 10.10.10.1 255.255.255.254

ON MY END (CORE)
int gig5/1
switchport trunk encapsulation dot1q
switch mode trunk

int vlan 50
ip vrf forwarding customer A
ip add 10.10.10.2 255.255.255.254.

Thanks

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Received on Tue Oct 06 2009 - 22:02:29 ART