Two NE40Es function as PEs and back up each
other. The two NE40Es are connected to two Ventor 7613 routers in a
square-shaped topology. Ventor 7613 routers function as Ps. Multiple VPN users,
including YH-BOSSOA-VPN, are connected to PEs. When VPN users access the external
network server, the ping operation on packets with the length less than 1964
succeeds, but the ping operation on packets with the length greater than 1964
1. Check that this symptom occurs on the VPN of the PE and applies to all
the packets transmitted over the PE.
2. Check that the outbound interface of the NE40E does
not work properly.
The default MTU values of devices from different vendors vary. For the
packets with the length greater than 1964 bytes, the bytes of the Ethernet
header are added. As a result, the total length is greater than 2000 bytes. Consequently all packets are discarded.
1. The packet header information shows that the NE40E properly sends data
packets to Ventor 7613 routers, but Ventor 7613 routers cannot receive the
2. Compare the configuration of the two devices. It is
found that the MTU value of the interface connecting the NE40E to the Ventor 7613 router is 2000, the MTU value of
the Ventor 7613 router is 1500, and the
MPLS MTU value is 2000.
3. Change the MTU value of the NE40E to resolve the
For the packets with the length greater than 1964 bytes,
the bytes of the Ethernet header are added. As a result, the total length is
greater than 2000 bytes. Consequently all
packets are discarded.
Huawei routers do not check the MTU upon receipt
of data packets. However, the MTU is used for sending packets. Ventor 7613
routers use MPLS MTU 2000 to match the received data packets. If the MTU of the
received packets is greater than 2000, such packets are discarded and the MPLS
labels cannot be fragmented and forwarded. Therefore, ensure MTU consistency in
the MPLS domain and ensure that the actual MTU is greater than the default
value of Huawei routers.