This document describes the inability of E-Series Ethernet cards to
stuff Ethernet frames in order to make them a legal 64 bytes. This problem
manifests itself in cases where there is a VLAN tagged on a port at one drop of
an Ethernet circuit and the same VLAN is untagged at another drop. This
document also provides a workaround for this problem.
There are no specific requirements for this document.
This document applies to all versions of E-series Ethernet cards for
the ONS15454 and ONS15327. This includes E100T-4, E100T-12, E100T-G, E1000-2,
It also applies to ALL versions of software and is totally independent
of any hardware combinations.
The information in this document was created from the devices in a
specific lab environment. All of the devices used in this document started with
a cleared (default) configuration. If your network is live, make sure that you
understand the potential impact of any command.
Refer to the
Technical Tips Conventions for more information on document
The inability to stuff Ethernet frames in order to make them legal (64
bytes) is seen in networks that have untagged ports on one side and tagged
ports on the other as this example shows.
Switch 1 --- E-Series Tagged --- SONET Ring --- E-Series Untagged --- Switch 2
Switch 1 sends a 64-byte Address Resolution Protocol (ARP) for the MAC
address of switch 2. The 64 byte frame consists of 60 bytes plus 4 bytes of
VLAN tag information. When this ARP arrives at the untagged Ethernet port, the
VLAN tag is removed since the port is untagged. This reduces the frame size to
60 bytes, which is illegal for Ethernet. Switch 2 drops the frame and
increments the "runt" counter. Most switches are able to detect that the frame
is illegal once the VLAN tag is removed and "stuff" the frame with an
additional 4 bytes of zeroes in order to make the frame a valid size of 64
Complete these steps in order to resolve this issue:
Configure both ends for "tagged" ports.
If you are unable to set both ends for tagged ports due to a switch
that is not able to understand VLAN tags, you can configure static ARP entries
in each switch. This allows the switch to know about the MAC address of the far
end switch without a need to perform an ARP.