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ATM Switch Router Software Configuration Guide
OL-7396-01
Chapter16 Configuring Tag Switching and MPLS
Configuring Tag Switching
Displaying the VP Tunnel Configuration
The following example shows PVP 51 on ATM interface 0/1/1 connected to PVP 101 on ATM
interface 0/1/3:
Switch# show atm vp
Interface VPI Type X-Interface X-VPI Status
ATM0/1/1 51 PVP ATM0/1/3 101 DOWN
ATM0/1/3 101 PVP ATM0/1/1 51 DOWN
Configuring VC Merge
VC merge allows the switch to aggregate multiple incoming flows with the same destination address into
a single outgoing flow. Where VC merge occurs, several incoming tags are mapped to one single
outgoing tag. Cells from different VCIs going to the same destination are transmitted to the same
outgoing VC using multipoint-to-point connections. This sharing of tags reduces the total number of
virtual circuits required for tag switching. Without VC merge, each source-destination prefix pair
consumes one tag VC on each interface along the path. VC merge reduces the tag space shortage by
sharing tags for different flows with the same destination.
Note VC merge support requires FC-PFQ on the route processor. If you do not have FC-PFQ, and you try to
enable VC merge, the TVCs remain point-to-point. (Catalyst 8510 MSR and LightStream 1010)
VC merge is enabled by default. To disable VC merge, enter the following command in global
configuration mode:

Displaying the VC Merge Configuration

To display the VC merge configuration, use the following EXEC command:
The following example shows that VC merge configuration is enabled on ATM interface 0/1/0:
Switch# show tag-switching atm-tdp capability
Control VPI VCI Alloc VC Merge
ATM0/1/0 VP VC Range Range Scheme IN OUT
Negotiated 0 32 [7 - 8] [33 - 1023] UNIDIR - -
Local - - [7 - 8] [33 - 16383] UNIDIR Yes Yes
Peer - - [7 - 8] [33 - 1023] UNIDIR - -
Command Purpose
no tag-switching atm vc-merge Disables VC merge.
Command Purpose
show tag-switching atm-tdp capability Displays the TDP control channel
configuration on an interface.