Configuring a VLL Service with CLI
Page 192 7210 SAS M Services Guide
Using Spoke SDP Control Words
Note: SDPs are not supported by 7210 SAS-M devices configured in Access Uplink mode.
The control word command provides the option to add a control word as part of the packet
encapsulation for PW types for which the control word is optional. These are Ethernet PW (epipe),
ATM N:1 cell mode PWs (Apipe vc-types atm-vcc and atm-vpc) and VT PW (Apipe vc-type atm-
cell). The control word might be needed because when ECMP is enabled on the network, packets
of a given PW may be spread over multiple ECMP paths if the hashing router mistakes the PW
packet payload for an IPv4 or IPv6 packet. This occurs when the first nibble following the service
label corresponds to a value of 4 or 6.
The control word negotiation procedures described in Section 6.2 of RFC 4447 are not supported
and therefore the service will only come up if the same C bit value is signaled in both directions. If
a spoke-sdp is configured to use the control word but the node receives a label mapping message
with a C-bit clear, the node releases the label with an “Illegal C-bit” status code per Section 6.1 of
RFC 4447. As soon as the user enables control of the remote peer, the remote peer withdraws its
original label and sends a label mapping with the C-bit set to 1 and the VLL service is up in both
nodes.
When the control word is enabled, VCCV packets also include the VCCV control word. In that
case, the VCCV CC type 1 (OAM CW) is signaled in the VCCV parameter in the FEC. If the
control word is disabled on the spoke-sdp, then the Router Alert label is used. In that case, VCCV
CC type 2 is signaled. Note that for a multi-segment PW (MS-PW), the CC type 1 is the only
supported and thus the control word must be enabled on the spoke-sdp to be able to use VCCV-
ping and VCCV-trace.
The following displays a spoke SDP control word configuration example:
-Dut-B>config>service>epipe# info
----------------------------------------------
description "Default epipe description for service id 2100"
sap 1/2/7:4 create
description "Default sap description for service id 2100"
exit
spoke-sdp 1:2001 create
control-word
exit
no shutdown
----------------------------------------------
*A:ALA-Dut-B>config>service>epipe#
To disable the control word on spoke-sdp 1:2001:
*A:ALA-Dut-B>config>service>epipe# info
----------------------------------------------
description "Default epipe description for service id 2100"
sap 1/2/7:4 create
description "Default sap description for service id 2100"
exit
spoke-sdp 1:2001 create
exit
no shutdown
----------------------------------------------
*A:ALA-Dut-B>config>service>epipe#
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