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Application Assurance — Asymmetry Removal
In This Chapter
This section describes Application Assurance asymmetry removal configurations.
Topics in this section include:
•
Applicability
•
Overview
•
Configuration
•
Conclusion
Applicability
This configuration note is applicable to all 7750 SR and 7450 ESS chassis supporting Application Assurance and was tested on release 11.0R1. Note that Asymmetry Removal is supported on 7750 SR-c12 but not on the 7750 SR-c4. For the Application Assurance Redundancy Protocol (AARP) feature, the diverting flexpath (FP) must be FP2 or higher as it makes use of spoke SDP divert.
The pre-requisites for this configuration note are a base understanding of AA configuration and operation for single homed deployments. This note applies to dual-homed SAPs and spoke SDPs configurations, in a business or residential AA context. AARP is not used for ESM AA subscribers.
 
Overview
This section is intended for Application Assurance (AA) network architects and engineers. It provides best practices recommendations to configure AA Asymmetry Removal.
Asymmetry means that the two directions of traffic for a given flow (to-sub and from-sub) take different paths through the network. Asymmetry removal is a means of eliminating traffic asymmetry between a set of dual-homed SAP or spoke SDP endpoints. This can be across endpoints within a single node or across a pair of inter-chassis link connected routers, which is the topology explained in this section. Asymmetry removal ensures all packets of a dual-homed AA subscriber are diverted to a given AA ISA in order to achieve accurate per subscriber traffic identification and policy enforcement.
Traffic asymmetry is created when there are dual-homed links for a given service, and the links are simultaneously carrying traffic. Asymmetry removal for transit subscribers must be implemented in the first routed hop on the network side of the subscriber management point, so there will be a deterministic and fixed SAP/spoke SDP representing the downstream subscriber management node. This ensures there are no more than two paths that the flows can take, both covered by the asymmetry removal solution.
Configuration
Application Assurance Redundancy Protocol (AARP) provides the data plane connectivity for dynamically keeping a dual-homed AA subscriber’s traffic on the same ISA-AA for AA processing. An AARP instance is configured between the dual-homed routers to establish connectivity with the same AARP instance number on each node.
When asymmetry exists between dual-chassis redundant systems, Ipipe spoke SDPs are used to interconnect these services between peer nodes over an Inter-Chassis Link (ICL). The following sections explain the configuration and operation of the services for use with the Application Assurance Redundancy Protocol.
 
AARP Service Configuration
The following services must be configured to establish communications between the AARP instances in each of the paired nodes.
•
Network topology is a VPRN (or IES) service configured in each node, with a dual-homed SAP from each node to a downstream access element.
•
Assumes starting point with AA ISAs installed with identical AA policy and divert enabled in each node.
•
Also, the system needs basic routing and LDP configuration for the SDP and the spoke SDPs to be established.
Figure 200: Application Assurance Asymmetry Removal Topology
 
Table 8: Application Assurance Asymmetry Removal Topology  
On PE-2
On PE-1
 
system ip: 10.1.1.2
system ip: 10.1.1.1
 
dual-homed service: 200
dual-homed service: 200
 
dual-homed sap: 1/1/4:200
dual-homed sap: 1/1/4:200
 
app-profile diverting: yes
app-profile diverting: yes
 
 
 
 
Configuration Commands for AARP
To enable AARP, AARP instances and AARP interfaces on both nodes must be configured. AARP operation has the following dependencies between the nodes:
•
Shunt links configured and operationally up, both subscriber side shunt and network side shunt.
•
Peer communications established between nodes, AARP instance operational status will be up when peers are communicating.
•
Dual-homed sap/spoke SDP configured with a unique AARP instance (matched by dual-homed interface).
•
App-profile configured against sap/spoke SDP with divert enabled (making the sub an aa-sub). The app-profile is the trigger to divert the traffic node with the active AARP instance to one of the ISAs in that node, per normal AA divert behavior.
 
 
Begin with PE-2:
configure 
        aarp 200 create
            description "aarp protecting a dual-homed sap"
            peer 10.1.1.1
            priority 100
            no shutdown
        exit
 
Ipipe shunt configuration
configure service 
        sdp 21 mpls create
            far-end 10.1.1.1
            ldp
            keep-alive
                shutdown
            exit
            no shutdown
        exit
        ipipe 210 customer 1 vc-switching create
            service-mtu 9174
            spoke-sdp 21:200 create
                aarp 200 type subscriber-side-shunt
                no shutdown
            exit
            spoke-sdp 21:201 create
                aarp 200 type network-side-shunt
                no shutdown
            exit
            no shutdown
        exit
Dual-homed and Interface Shunt Configuration
        vprn 200 customer 1 create
            description "VPRN 200 Dual Homed Routed Service"
            interface "bras1" create
                sap 1/1/10:4 create
                    app-profile "appProf1"
                    aarp 200 type dual-homed
                exit
            exit
            aarp-interface "subside_1" create
                spoke-sdp 21:212 create
                    aarp 200 type subscriber-side-shunt
                    no shutdown
                exit
            exit
            aarp-interface "netside_1" create
                spoke-sdp 21:213 create
                    aarp 200 type network-side-shunt
                    no shutdown
                exit
            exit
 
Then similarly configure the associated AARP configuration on PE-1:
configure
    application-assurance
        aarp 200 create
            description "aarp protecting a dual-homed sap"
            peer 10.1.1.2
            priority 200
            no shutdown
        exit
 
Ipipe Shunt Configuration
        sdp 12 mpls create
            far-end 10.1.1.2
            ldp
            keep-alive
                shutdown
            exit
            no shutdown
        exit
        ipipe 210 customer 1 vc-switching create
            service-mtu 9174
            spoke-sdp 12:212 create
                aarp 200 type subscriber-side-shunt
                no shutdown
            exit
            spoke-sdp 12:213 create
                aarp 200 type network-side-shunt
                no shutdown
            exit
            no shutdown
        exit
Dual-homed and Interface Shunt Configuration
vprn 200 customer 1 create
            interface "bras1" create
                sap 1/1/4:200 create
                    description "AA enabled SAP"
                    aarp 200 type dual-homed
                    app-profile "appProf1"
                exit
            exit
            aarp-interface "subside_1" create
                spoke-sdp 12:200 create
                    aarp 200 type subscriber-side-shunt
                    no shutdown
                exit
            exit
            aarp-interface "netside_1" create
                spoke-sdp 12:201 create
                    aarp 200 type network-side-shunt
                    no shutdown
                exit
            exit
 
Show Commands for AARP
Verify correct configuration on each node. The following output displays the example configuration for PE-1.
Starting with the AARP instance in each node, verify that the AARP instance operational state is up (if everything is properly configured as intended):
*A:PE-1# show application-assurance aarp 200
========================================================================
AARP Instance 200
========================================================================
Description    : aarp protecting dual homed sap
Admin State    : Up                     Oper State     : Up
 
Local IP       : 10.1.1.1               Peer IP        : 10.1.1.2
Local State    : master                 Peer State     : backup
Local Priority : 200                    Peer Priority  : 100
 
Local Flags    : none
Peer Flags     : none
Peer End-Point : none
 
Master Selection Mode       : minimize-switchovers
-------------------------------------------------------------------------------
Service References
-------------------------------------------------------------------------------
Service              Reference            Reference Type
-------------------------------------------------------------------------------
VPRN 200             1/1/4:200            Dual-Homed
Ipipe 210            12:212               Subscriber-Side Pipe Shunt
Ipipe 210            12:213               Network-Side Pipe Shunt
VPRN 200             12:200               Subscriber-Side AARP-Interface Shunt
VPRN 200             12:201               Network-Side AARP-Interface Shunt
-------------------------------------------------------------------------------
No. of service references: 5
 
Verifying that the AARP instance is up is an indication that the dual-node communications for AARP is working (instance, shunts, etc.). In addition, in the above output, verify on both PE nodes that the intended SAPs are dual-homed for that instance.
Now a detailed review of the configured AARP shunt infrastructure services can be shown to make sure they are all properly configured with intended AARP parameters (such as AARP ID and Type on the network and subscriber side shunts) as displayed in the following output:
*A:PE-1>show# service id 210 all
===============================================================================
Service Detailed Information
===============================================================================
Service Id        : 210                 Vpn Id            : 0
Service Type      : Ipipe
Name              : (Not Specified)
Description       : (Not Specified)
Customer Id       : 1                   Creation Origin   : manual
Last Status Change: 05/29/2013 12:48:25
Last Mgmt Change  : 05/27/2013 13:47:32
Admin State       : Up                  Oper State        : Up
MTU               : 9174
Vc Switching      : True
SAP Count         : 0                   SDP Bind Count    : 2
CE IPv4 Discovery : n/a
CE IPv6 Discovery : n/a                 Stack Cap Sig     : n/a
-------------------------------------------------------------------------------
ETH-CFM service specifics
-------------------------------------------------------------------------------
Tunnel Faults     : ignore
-------------------------------------------------------------------------------
Service Destination Points(SDPs)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
 Sdp Id 12:212  -(10.1.1.2)
-------------------------------------------------------------------------------
Description     : (Not Specified)
SDP Id             : 12:212                   Type              : Spoke
Spoke Descr     : (Not Specified)
Split Horiz Grp    : (Not Specified)
VC Type            : Ipipe                    VC Tag            : 0
Admin Path MTU     : 0                        Oper Path MTU     : 9174
Delivery           : MPLS
Far End            : 10.1.1.2
Tunnel Far End     : 10.1.1.2                 LSP Types         : LDP
Hash Label         : Disabled                 Hash Lbl Sig Cap  : Disabled
Oper Hash Label    : Disabled
 
Admin State        : Up                       Oper State        : Up
...
Application Profile: None
Transit Policy     : None
AARP Id            : 200
AARP Type          : subscriber-side-shunt
...
-------------------------------------------------------------------------------
IPIPE Service Destination Point specifics
-------------------------------------------------------------------------------
Configured CE IPv4 Addr: n/a                  Peer CE IPv4 Addr : 0.0.0.0
-------------------------------------------------------------------------------
 Sdp Id 12:213  -(10.1.1.2)
-------------------------------------------------------------------------------
Description     : (Not Specified)
SDP Id             : 12:213                   Type              : Spoke
Spoke Descr     : (Not Specified)
Split Horiz Grp    : (Not Specified)
VC Type            : Ipipe                    VC Tag            : 0
Admin Path MTU     : 0                        Oper Path MTU     : 9174
Delivery           : MPLS
Far End            : 10.1.1.2
Tunnel Far End     : 10.1.1.2                 LSP Types         : LDP
Hash Label         : Disabled                 Hash Lbl Sig Cap  : Disabled
Oper Hash Label    : Disabled
 
Admin State        : Up                       Oper State        : Up
...
Application Profile: None
Transit Policy     : None
AARP Id            : 200
AARP Type          : network-side-shunt
...
 
Next, the configuration of the VPRN service of the dual-homed SAP can be reviewed to ensure it reflects the attached endpoints for the shunt Ipipe spoke SDPs:
*A:PE-1>show>service>id 200 all
===============================================================================
Service Detailed Information
===============================================================================
Service Id        : 200                 Vpn Id            : 0
Service Type      : VPRN
Name              : (Not Specified)
Description       : (Not Specified)
Customer Id       : 1                   Creation Origin   : manual
Last Status Change: 05/27/2013 13:47:32
Last Mgmt Change  : 05/27/2013 13:47:32
Admin State       : Up                  Oper State        : Up
 
Route Dist.       : 65004:1             VPRN Type         : regular
AS Number         : None                Router Id         : 10.1.1.1
ECMP              : Enabled             ECMP Max Routes   : 1
Max IPv4 Routes   : No Limit            Auto Bind         : LDP
Max IPv6 Routes   : No Limit
Ignore NH Metric  : Disabled
Hash Label        : Disabled
Vrf Target        : target:65004:200
Vrf Import        : None
Vrf Export        : None
MVPN Vrf Target   : None
MVPN Vrf Import   : None
MVPN Vrf Export   : None
Car. Sup C-VPN    : Disabled
Label mode        : vrf
BGP VPN Backup    : Disabled
 
SAP Count         : 4                   SDP Bind Count    : 2
...
 
-------------------------------------------------------------------------------
Service Destination Points(SDPs)
-------------------------------------------------------------------------------
-------------------------------------------------------------------------------
 Sdp Id 12:200  -(10.1.1.2)
-------------------------------------------------------------------------------
Description     : (Not Specified)
SDP Id             : 12:200                   Type              : Spoke
Spoke Descr     : (Not Specified)
VC Type            : n/a                      VC Tag            : n/a
Admin Path MTU     : 0                        Oper Path MTU     : 9174
Delivery           : MPLS
Far End            : 10.1.1.2
Tunnel Far End     : 10.1.1.2                 LSP Types         : LDP
Hash Label         : Disabled                 Hash Lbl Sig Cap  : Disabled
Oper Hash Label    : Disabled
 
Admin State        : Up                       Oper State        : Up
...
Application Profile: None
Transit Policy     : None
AARP Id            : 200
AARP Type          : subscriber-side-shunt
 
...
-------------------------------------------------------------------------------
IPIPE Service Destination Point specifics
-------------------------------------------------------------------------------
Configured CE IPv4 Addr: n/a                  Peer CE IPv4 Addr : 0.0.0.0
-------------------------------------------------------------------------------
 Sdp Id 12:201  -(10.1.1.2)
-------------------------------------------------------------------------------
Description     : (Not Specified)
SDP Id             : 12:201                   Type              : Spoke
Spoke Descr     : (Not Specified)
VC Type            : n/a                      VC Tag            : n/a
Admin Path MTU     : 0                        Oper Path MTU     : 9174
Delivery           : MPLS
Far End            : 10.1.1.2
Tunnel Far End     : 10.1.1.2                 LSP Types         : LDP
Hash Label         : Disabled                 Hash Lbl Sig Cap  : Disabled
Oper Hash Label    : Disabled
 
Admin State        : Up                       Oper State        : Up
...
 
Application Profile: None
Transit Policy     : None
AARP Id            : 200
AARP Type          : network-side-shunt
...
 
Continuing deeper into the same VPRN service show output, it can be verified that the dual-homed SAP itself is properly configured and associated with that service and AARP instance:
-------------------------------------------------------------------------------
SAP 1/1/4:200
-------------------------------------------------------------------------------
Service Id         : 200
SAP                : 1/1/4:200                Encap             : q-tag
Description        : (Not Specified)
Admin State        : Up                       Oper State        : Up
Flags              : PortOperDown
Multi Svc Site     : None
Last Status Change: 05/27/2013 13:47:32
Last Mgmt Change  : 05/27/2013 13:47:32
Sub Type           : regular
Dot1Q Ethertype    : 0x8100                   QinQ Ethertype    : 0x8100
Split Horizon Group: (Not Specified)
 
Admin MTU          : 1518                     Oper MTU          : 1518
Ingr IP Fltr-Id    : n/a                      Egr IP Fltr-Id    : n/a
Ingr Mac Fltr-Id   : n/a                      Egr Mac Fltr-Id   : n/a
Ingr IPv6 Fltr-Id  : n/a                      Egr IPv6 Fltr-Id  : n/a
BGP IPv4 FlowSpec  : Disabled
BGP IPv6 FlowSpec  : Disabled
tod-suite          : None                     qinq-pbit-marking : both
                                              Egr Agg Rate Limit: max
Q Frame-Based Acct : Disabled
 
Acct. Pol          : None                     Collect Stats     : Disabled
 
Anti Spoofing      : None                     Dynamic Hosts     : Enabled
Avl Static Hosts   : 0                        Tot Static Hosts  : 0
Calling-Station-Id : n/a
 
Application Profile: appProf1
Transit Policy     : ip 200
AARP Id            : 200
AARP Type          : dual-homed
 
Oper Group         : (none)                   Monitor Oper Grp  : (none)
Host Lockout Plcy  : n/a
Lag Link Map Prof  : (none)
...
 
Network to Subscriber Traffic Flow
When the AARP is operationally up, AARP tracks which ISA is the master ISA for each dual-homed AARP instance and uses the inter-chassis services (spoke SDP AARP shunts) to move all traffic for each instance traffic to the node with the Master ISA.
Looking at traffic in the network to subscriber direction (Figure 201):
•
Traffic arriving on PE-1 is diverted to the local master ISA, processed, then proceeds to the egress SAP.
•
Traffic arriving on PE-2 with the backup AARP interface is sent to the master node for AA processing. The ingress FP forwards packets to network-side-shunt AARP interface for remote AA divert.
•
Arriving on PE-1, the packets on the AARP Ipipe are diverted to the master ISA where the packets are processed as if this traffic was travelling in the to-sub direction towards the dual-homed endpoint on PE-1, then returned to PE-2.
•
Entering PE-2, the traffic from the subscriber side shunt interface is not diverted to ISAs in that node and egresses on the AARP instance SAP.
With this behavior, traffic always returns to the original ingress node before egressing toward the subscriber (network path for the flows are not modified).
Figure 201: Network to Subscriber Traffic Flow
Subscriber to Network Traffic Flow
Looking at traffic in the subscriber to network direction (Figure 202):
•
Traffic arriving on PE-1 is diverted to the local master ISA, processed, then proceeds to the egress SAP.
•
Traffic arriving on PE-2 with the backup AARP ISA is sent to the master node for AA processing (not diverted to an ISA in PE-2). The ingress FP forwards packets to subscriber-side-shunt AARP interface for remote AA divert.
•
Arriving on PE-1, the packets on the AARP Ipipe are diverted to the master ISA where the packets are processed as if the traffic was flowing in the from-sub direction on the dual-homed endpoint, then returned to PE-2 over the Ipipe’s AARP subscriber-side-shunt.
•
Entering PE-2, the traffic from the network side shunt interface is forwarded by the IES/VPRN service to its destination.
Figure 202: Subscriber to Network Traffic Flow
 
Typical Configuration Mistakes
Operators configuring AARP can make some typical mistakes listed below that will keep the AARP instance in Operational State down:
•
The spoke SDP AARP shunt instances’ IDs must be aligned with the respective spoke SDP on the peer node: if not, it will result in a flag indicating shunt mismatch in the show output.
•
Ipipe service MTU alignment — The Ipipe service MTU values must be the same in both nodes, otherwise it will result in the services be in operational status UP, but the AARP instance will remain down.
 
Conclusion
This section is intended for Application Assurance (AA) network architects and engineers to provide the information required to understand and configure dual-node asymmetry removal following the intended service configuration as used by the AARP implementation.