Document ID: 10491
Contents
Introduction
Prerequisites
Requirements
Components Used
Conventions
Circuit Bumping
Implicit Bumping
Explicit Bumping
Additional Bumping Information
Bring the PVC Down
Bundle's Protected Group
Individually-protected VC Bundle Member
debug and show Commands
Related Information
Introduction
ATM Permanent Virtual Circuit (PVC) bundles allow you to configure multiple PVCs that have different Quality of Service (QoS) characteristics between two devices. The purpose is to bind a PVC from the bundle to one or more precedence values. To determine which VC in the bundle is used to forward specific traffic, the ATM VC bundle management software matches precedence levels between packets and VCs.
The ATM virtual bundle acts as a single routing link to the destination router. The Operation and Maintenance (OAM) polling mechanism individually monitors the integrity of each circuit individually. If a VC becomes unavailable, the router can avoid losing data in two ways:
The purpose of this document is to explain in detail the concepts behind PVC bundle protection. Refer to PVC Bundle Protection for more information.
Prerequisites
Requirements
There are no specific requirements for this document.
Components Used
The information in this document is based on these software and hardware versions:
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7500:
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All PA-A3 versions. Requires VIP2-50, VIP4-50, VIP4-80 or later. Only one PA-A3 per VIP2-50. Requires Cisco IOS® Software Release 12.0(3)T and later.
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All PA-A6 versions. Requires VIP4, RSP8 and later. Requires Cisco IOS Software Release 12.2(15)T, 12.3(1) and later.
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7200/7200VXR:
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All PA-A3 versions. NPE200 or higher, Requires Cisco IOS Software Release 12.0(3)T and later.
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All PA-A6 versions. 7200VXR: NPE400, NSE-1, NPE-G1. Requires Cisco IOS Software Release 12.2(15)T, 12.3(1) and later.
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Catalyst 6500/7600:
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FlexWan and Enhanced FlexWan with PA-A3. Supported with MSFC2 in Cisco IOS Software Release 12.1(13)E13 and later.
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FlexWan and Enhanced FlexWan with PA-A6. Supported on SUP2 and SUP720 in Cisco IOS Software Release 12.2(14)SX and later.
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7401ASR:
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All PA-A6 versions. Requires Cisco IOS Software Release 12.3(1) and later.
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All PA-A3 versions. Supported in all Cisco IOS Software releases.
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Cisco 2600 and 3600:
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NM-1A-OC3, NM-4E1-IMA, NM-4T1-IMA, NM-8E1-IMA, NM-8T1-IMA network modules. Requires Cisco IOS Software Release 12.0(7)T or later.
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NM-1A-T3 and NM-1A-E3 network modules. Requires Cisco IOS Software Release 12.1(2)T or later.
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Cisco 12000:
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Cisco 12000 8-port OC-3c/STM1 ATM Line Card. Cisco IOS Software Release 12.0(23)S or later.
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Cisco 12000 4 -port OC-3c/STM-1c ATM ISE Line Card. Cisco IOS Software Release 12.0(27)S or later.
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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.
Conventions
For more information on document conventions, refer to the Cisco Technical Tips Conventions.
Circuit Bumping
Circuit bumping assigns the traffic bound to a failed VC to another VC. The two bumping methods are explicit bumping and implicit bumping.
In order to illustrate bumping, this setup is used:
Two PVCs are created between Ema and Bernard (two 7507s that use a PA-A3 in a VIP2-50 and run Cisco IOS Software Release 12.0(7)T). These two PVCs are assigned the values 1/130 and 1/131 on both ends of the connection. To simplify, 1/130 is switched to 1/130 by the ATM switch and 1/131 is switched to 1/131.
The PVC 1/130 is configured as a VBR-nrt VC and 1/131 as an ABR VC. The precedence values 0 to 4 are bound to PVC 1/130 and precedence values 5 to 7 to the PVC 1/131. The Per-VC DWRED is used to discard packets.
Implicit Bumping
In case there is a VC failure, implicit bumping (which is the default) diverts the traffic to a VC in charge of a lower precedence value. Here are the configuration lines necessary to enable this protection method (configuration taken from Bernard, similar to the configuration that exists on Ema) if the traffic generator sends two streams of data, one with precedence 5 and one with precedence 3:
interface ATM2/0/0.6 point-to-point
bundle bernard
oam-bundle manage
pvc-bundle 1/131
random-detect attach testWRED
precedence 5-7
bump implicit
bump traffic
pvc-bundle 1/130
random-detect attach testWRED
precedence 0-4
bump implicit
bump traffic
The PVC 1/131 is brought down and this should cause the precedence 5 traffic to go over 1/130.
Normal Situation
bernard#show atm bundle
bernard on ATM2/0/0.6: UP
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
3 1/131 7-5 7-5 4 / Yes - 1000 100 UP
6 1/130 4-0 4-0 - / Yes - 100000 100000 94 UP
Note: Go to the Additional Bumping section for an explanation of the output above.
bernard#show queuing interface atm 2/0/0.6
Interface ATM2/0/0.6 VC 1/131
Exp-weight-constant: 2 (1/4)
Mean queue depth: 781
Queue size: 776 Maximum available buffers: 2628
Output packets: 1309 WRED drops: 217 No buffer: 73982
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 0 0 100 1000 1/3 0
4 0 0 28 40 1/10 0
5 217 0 200 1000 1/5 2616
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
Interface ATM2/0/0.6 VC 1/130
Exp-weight-constant: 2 (1/4)
Mean queue depth: 0
Queue size: 0 Maximum available buffers: 2628
Output packets: 3037 WRED drops: 0 No buffer: 72478
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 0 0 100 1000 1/3 3037
4 0 0 28 40 1/10 0
5 0 0 200 1000 1/5 0
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
Traffic flows on the appropriate VC. In other words, IP precedence 3 traffic flows across PVC 1/130 and IP precedence 5 traffic flows through PVC 1/131 as configured.
At this point, PVC 1/131 is brought down.
As you can see, there are no more packets on 1/131.
bernard#show queuing interface atm 2/0/0.6
Interface ATM2/0/0.6 VC 1/131
Exp-weight-constant: 2 (1/4)
Mean queue depth: 779
Queue size: 778 Maximum available buffers: 2628
Output packets: 2618 WRED drops: 436 No buffer: 147848
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 0 0 100 1000 1/3 0
4 0 0 28 40 1/10 0
5 436 0 200 1000 1/5 2616
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
Interface ATM2/0/0.6 VC 1/130
Exp-weight-constant: 2 (1/4)
Mean queue depth: 264
Queue size: 265 Maximum available buffers: 2628
Output packets: 36666 WRED drops: 657 No buffer: 164145
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 498 0 100 1000 1/3 23252
4 0 0 28 40 1/10 0
5 159 0 200 1000 1/5 13679
!--- IP precedence 5 traffic is redirected.
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
In this case, as PVC 1/131 has been brought down, the stream with IP precedence = 5 has been re-directed to PVC 1/130. In other words, IP precedence = 5 traffic is sent across a PVC which is responsible for a lower precedence value. The same happens to traffic with an IP precedence that ranges from 5 to 7.
Important!: With such a method, the traffic that corresponds to IP precedence = 0 is not diverted to another VC and is therefore lost. To protect such traffic, use the explicit bumping method.
Explicit Bumping
In case of a VC failure, you can force the traffic of a failed VC to a specific one rather than let a stream that corresponds to an IP precedence automatically go to a VC that carries a lower IP precedence value. In other words, you manually specify the precedence level to which traffic on a VC (bundle-vc mode) is bumped when the VC goes down. This is called explicit bumping.
The command to enable explicit bumping is bump explicit [precedence value]. Here are the configuration lines necessary to enable this protection method (configuration taken from Bernard, similar to the Ema configuration). In this case, PVC 1/130 is configured for explicit bumping while PVC 1/131 keeps the implicit bumping method:
interface ATM2/0/0.6 point-to-point bundle bernard oam-bundle manage pvc-bundle 1/131 random-detect attach testWRED precedence 5-7 bump implicit bump traffic pvc-bundle 1/130 random-detect attach testWRED precedence 0-4 bump explicit 6 bump traffic
This configuration means that if PVC 1/130 fails, the traffic of this VC is carried by the VC in charge of carrying IP precedence 6 traffic.
To show the results, the traffic generator sends two streams of data, one with precedence 5 and one with precedence 3. The next section discusses what happens on Bernard if PVC 1/130 fails.
Normal situation, PVC 1/130 is up.
bernard#show atm bundle
bernard on ATM2/0/0.6: UP
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
3 1/131 7-5 7-0 - / Yes - 1000 100 UP
6 1/130 4-0 6 / Yes - 100000 100000 94 UP
The show atm bundle command allows you to see the bumping method that you configured. Here you can see that PVC 1/130 has been configured for explicit bumping to the PVC in charge of IP precedence 6.
bernard#show queuing interface atm 2/0/0.6
Interface ATM2/0/0.6 VC 1/131
Exp-weight-constant: 2 (1/4)
Mean queue depth: 780
Queue size: 493 Maximum available buffers: 2628
Output packets: 10159 WRED drops: 274 No buffer: 43004
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 0 0 100 1000 1/3 0
4 0 0 28 40 1/10 0
5 273 0 200 1000 1/5 2123
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
Interface ATM2/0/0.6 VC 1/130
Exp-weight-constant: 2 (1/4)
Mean queue depth: 0
Queue size: 0 Maximum available buffers: 2628
Output packets: 5090 WRED drops: 0 No buffer: 40314
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 0 0 100 1000 1/3 5090
4 0 0 28 40 1/10 0
5 0 0 200 1000 1/5 0
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
Each PVC carries its own traffic.
This output brings down PVC 1/130.
bernard#show atm bundle
bernard on ATM2/0/0.6: UP
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
3 1/131 7-5 7-0 - / Yes - 1000 100 UP
6 1/130 4-0 6 / Yes - 100000 100000 94 DOWN
bernard#show queuing interface atm 2/0/0.6
Interface ATM2/0/0.6 VC 1/131
Exp-weight-constant: 2 (1/4)
Mean queue depth: 780
Queue size: 783 Maximum available buffers: 2628
Output packets: 12332 WRED drops: 733 No buffer: 152725
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 289 0 100 1000 1/3 1189
!--- IP precedence 3 traffic has been redirected.
4 0 0 28 40 1/10 0
5 443 0 200 1000 1/5 3381
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
Interface ATM2/0/0.6 VC 1/130
Exp-weight-constant: 2 (1/4)
Mean queue depth: 0
Queue size: 0 Maximum available buffers: 2628
Output packets: 5090 WRED drops: 0 No buffer: 40314
Class Random Tail Minimum Maximum Mark Output
drop drop threshold threshold probability Packets
0 0 0 20 40 1/10 0
1 0 0 22 40 1/10 0
2 0 0 24 40 1/10 0
3 0 0 100 1000 1/3 5090
4 0 0 28 40 1/10 0
5 0 0 200 1000 1/5 0
6 0 0 32 40 1/10 0
7 0 0 34 40 1/10 0
IP precedence 3 traffic now flows through PVC 1/131. This traffic has been explicitly bumped to the PVC in charge of carrying IP precedence = 6 traffic. The advantage of this method is that you can choose which VC carries the traffic of a failed VC. In other words, this allows you to choose a VC which provides a QoS similar to the one that the failed VC provided.
Additional Bumping Information
When you configure bumping, you can also make sure that bumped traffic does not have an impact on sensitive traffic on another PVC. It is possible for you to make sure that certain VCs never carry bumped traffic. This can be achieved by the use of the no bump traffic command.
interface ATM2/0/0.6 point-to-point bundle bernard pvc-bundle 1/130 bump explicit 6 no bump traffic
The configuration example above means that PVC 1/130 bumps its traffic to the PVC in charge of IP precedence 6. Furthermore, this PVC does not accept bump traffic that comes from another PVC. You can verify the bumping configuration using the show atm bundle command:
Note: This output is not related to the setup used for previous examples.
bernard#show atm bundle
bernard on ATM2/0/0.6: UP
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
8 1/132
7-5
4 / No - 149760 DOWN
9 1/131
4-2
7-2 1 / Yes - 1000 100 UP
10 1/130
1-0
1-0 2 / Yes - 100000 100000 94 UP
These conclusions are made from the show atm bundle output:
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You can see the precedence value(s) assigned to each PVC.
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You can see to which precedence (in the blue font) the traffic of a VC is bumped.
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You can also see whether a PVC does or does not accept bumped traffic.
From this output, you can observe that a failure occurred (PVC 1/132 DOWN). Due to this failure, PVC 1/131 now transports traffic which was previously assigned to PVC 1/132. In other words, PVC 1/131 now transports traffic with IP precedence between 2 and 7.
Bring the PVC Down
When a failure occurs on a VC, there is a second method of protection. This time, instead of redirecting the affected traffic onto another VC, the bundle is brought down. By doing this, you rely on the routing protocol to re-direct the affected traffic onto another connection.
The two methods are bundle's protected group or individually protected VC bundle member. In order to illustrate this, this setup is used:
Three PVCs are created between Ema and Bernard (two 7507s that use a PA-A3 in a VIP2-50 and run Cisco IOS Software Release 12.0(7)T). These three PVCs have been assigned the values 1/129, 1/130 and 1/131 on both ends of the connection. For the sake of clarity, 1/129 is switched to 1/129 by the ATM switch, 1/130 is switched to 1/130, and 1/131 is switched to 1/131.
The PVC 1/129 is a simple UBR PVC, 1/130 is configured as a VBR-nrt VC, and 1/131 as an ABR VC. The precedence values 1 to 4 are bound to PVC 1/130, precedence values 5 to 7 to the PVC 1/131, and precedence 0 to 1/129. Per-VC DWRED is used as a packet discard mechanism.
Bundle's Protected Group
In this method, you assign a VC into a protected group. If all the VCs which are part of a protected group go down, the entire bundle goes down. Here are the configuration lines necessary to enable this protection method (configuration taken from Bernard, a similar configuration exists on Ema). In this case, PVC 1/130 and PVC 1/131 are members of one protected group:
interface ATM2/0/0.6 point-to-point bundle bernard oam-bundle manage pvc-bundle 1/131 protect group pvc-bundle 1/130 protect group
This is what you observe when a failure occurs on a VC that is part of such a protected group:
Normal Situation
bernard#show atm bundle
bernard on ATM2/0/0.6: UP
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
8 1/131 7-5 7-5 0 / No PG 1000 100 UP
9 1/130 4-1 4-1 0 / No PG 100000 100000 94 UP
10* 1/129 0 0 - / No - 149760 UP
You can verify here that PVC 1/130 and 1/131 are part of a protected group.
PVC 1/131 is brought down.
bernard on ATM2/0/0.6: UP
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
8 1/131 7-5 0 / Yes PG 1000 100 DOWN
9 1/130 4-1 4-1 0 / Yes PG 100000 100000 94 UP
10* 1/129 0 7-5, 0 - / Yes - 149760 UP
PVC 1/131 is down, but PVC 1/130 is up. Therefore, the bundle stays up and traffic from PVC 1/131 is normally bumped to 1/129. The bumping method is the explicit bumping to the PVC in charge of IP precedence = 0.
PVC 1/131 and 1/130 are brought down.
bernard#show atm bundle
bernard on ATM2/0/0.6: DOWN, PG down
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
8 1/131 7-5 0 / Yes PG 1000 100 DOWN
9 1/130 4-1 0 / Yes PG 100000 100000 94 DOWN
10* 1/129 0 - / Yes - 149760 UP
bernard#show interface atm 2/0/0.6
ATM2/0/0.6 is down, line protocol is down
Hardware is cyBus ENHANCED ATM PA
Internet address is 14.0.0.1/8
MTU 4470 bytes, BW 149760 Kbit, DLY 80 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ATM
72 packets input, 6640 bytes
70 packets output,6560 bytes
1137 OAM cells input, 1296 OAM cells output
In this case, both PVCs that belong to the protection group are down. This caused the bundle to go down (DOWN, PG down) along with the sub-interface.
Note: When you configure bundle protection, you have to remember to also configure bumping on the PVC's part of the protection group. Also, if one of these PVCs goes down but the bundle stays up, the traffic of the failed PVC has to be re-directed to another PVC to keep the integrity of the affected streams. If bumping is not configured, the traffic on the failed PVC cannot be forwarded. This causes the bundle to go down.
This output shows that PVC 1/131 is brought down, PVC 1/130 is up (so the bundle should remain up), but bumping is not configured:
bernard#show atm bundle
bernard on ATM2/0/0.6: DOWN, Bumping exhausted
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
8 1/131 7-5 - / No PG 1000 100 DOWN
9 1/130 4-1 - / No PG 100000 100000 94 UP
10* 1/129 0 - / No - 149760 UP
As you can see, the whole bundle has been brought down.
Individually-protected VC Bundle Member
In this case, if an individually-protected VC goes down, the whole bundle is brought down. Here are the configuration lines necessary to enable this protection method (configuration taken from Bernard, a similar configuration exists on Ema). In this case, PVC 1/130 is the individually-protected VC:
interface ATM2/0/0.6 point-to-point bundle bernard oam-bundle manage pvc-bundle 1/130 protect vc
This is what you can observe when a failure occurs on PVC 1/130:
Normal situation:
bernard#show atm bundle
bernard on ATM2/0/0.6: UP
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
8 1/131 7-5 7-5 - / No - 1000 100 UP
9 1/130 4-1 4-1 - / No PV 100000 100000 94 UP
10* 1/129 0 0 - / No - 149760 UP
You can see that PVC 1/130 is configured as a protected VC.
PVC 1/130 is brought down.
bernard#show atm bundle
bernard on ATM2/0/0.6: DOWN, PV down
Config Current Bumping PG/ Peak Avg/Min Burst
VC Name VPI/ VCI Preced. Preced. Preced./ PV Kbps kbps Cells Sts
Accept
8 1/131 7-5 - / No - 1000 100 UP
9 1/130 4-1 - / No PV 100000 100000 94 DOWN
10* 1/129 0 - / No - 149760 UP
bernard#show interface atm 2/0/0.6
ATM2/0/0.6 is down, line protocol is down
Hardware is cyBus ENHANCED ATM PA
Internet address is 14.0.0.1/8
MTU 4470 bytes, BW 149760 Kbit, DLY 80 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation ATM
86 packets input, 7880 bytes
82 packets output,7700 bytes
1465 OAM cells input, 1666 OAM cells output
As you can see, the whole bundle and the corresponding sub-interface has been brought down.
debug and show Commands
Certain show commands are supported by the Output Interpreter Tool (registered customers only) , which allows you to view an analysis of show command output.
Note: Before issuing debug commands, refer to Important Information on Debug Commands.
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show atm bundle [bundle name] —Displays the bundle attributes assigned to each bundle virtual circuit (VC) member and the current working status of the VC members.
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show atm pvc vpi/vci —Displays all ATM permanent virtual connections (PVCs) and traffic information as well as ATM virtual path identifier (VPI) and virtual channel identifier (VCI) numbers.
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debug atm bundle events—Displays switched virtual circuit (SVC) bundle events.
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debug atm bundle errors—Displays debug messages for SVC bundle errors.
Related Information
| Updated: Nov 15, 2007 | Document ID: 10491 |