The infrastructure of a service provider must be capable of supporting the services that an enterprise customer or Internet service provider (ISP) wants to offer its subscribers. The service provider must also be able to scale up to an expanding subscriber base. You can configure the Cisco ASR1000 Series Routers for high broadband scalability.
Your software release might not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the “Feature Information for Broadband Scalability and Performance” section.
The ASR 1000 Series Routers are deployed in a variety of broadband deployment models for terminating Point-to-Point Protocol (PPP) Sessions and initiating or terminating Layer 2 Tunneling Protocol (L2TP) tunnels. The maximum number of PPP sessions and L2TP tunnels is dependent on the hardware combination. Table 8-1 lists the hardware combinations and the maximum number of PPP sessions and L2TP tunnels that are supported in Cisco IOS XE Release 3.3. For information about the restrictions for PPP sessions and L2TP tunnel scaling, see the “Restrictions for PPP Sessions and L2TP Tunnel Scaling” section.
1.32000 session scaling with RP2 and ESP-40G is fully supported without any additional restrictions. For restrictions on 48000 and 64000 see the “Restrictions for PPP Sessions and L2TP Tunnel Scaling” section.
Table 8-2 lists the virtual circuit limits for ASR 1000 ATM SPAs, effective from Cisco IOS XE Release 3.5.
This section lists the restrictions for the PPP sessions and L2TP tunnel scalability.
To achieve maximum scaling for the 1001, 1002, and 1004 chassis, we recommend software redundancy be disabled for broadband applications, and only hardware redundancy be configured.
Note If any of the listed restrictions is not met, the router scales to a maximum of 32000 sessions only.
Note If any of the listed restrictions is not met, the router scales to a maximum of 32000 sessions or 48000 sessions only.
Note If any of the listed restrictions is not met, the router scales to a maximum of 16000 L2TP tunnels.
The RP2 and ESP10 hardware combination is not supported for broadband.
RP1 with 2GB of DRAM is not recommended for broadband deployment.
The Cisco ASR 1000 Series Routers provide powerful performance and scalability for embedded services.
To achieve maximum scaling on the 1001, 1002, and 1004 chassis, IOS software redundancy must be disabled. For more information about restrictions and limitations, see the “Restrictions for PPP Sessions and L2TP Tunnel Scaling” section.
The Call Admission Control (CAC) feature is configured to protect the ASR 1000 processing resources that must be configured. CAC can restrict the media bandwidth dedicated to active calls when CPU utilization exceeds the configured threshold.
The Control Plane Policing feature allows you to configure a QoS filter that manages the traffic flow of control plane packets to protect the control plane of Cisco IOS XE routers and switches against reconnaissance and denial-of-service (DoS) attacks. The control plane thus helps maintain packet forwarding and protocol states despite an attack or heavy traffic load on the router or switch.
Using the Virtual Private Dialup Network (VPDN) Group Session Limiting feature, you can limit the number of VPDN sessions allowed per VPDN group. VPDN session limits can increase performance and reduce latency for routers that are otherwise forced to operate at high capacity.
The PPPoE Session Limit Support feature prevents the router from using too much memory for virtual access by limiting the number of PPPoE sessions that can be created on a router or on all Ethernet interfaces and subinterfaces as well as ATM interfaces and subinterfaces.
To prevent the virtual access subinterfaces from being registered with the Simple Network Management Protocol (SNMP) functionality of the router and using up the memory, do not use the SNMP management tools of the router to monitor PPP sessions. Use SNMP views to isolate the bulk queries and accidental requests.
When you configure this command, the router directly queues the L2TP Hello packets and Hello acknowledgements to the L2TP control process. We recommend that you configure this command in all the scaled LAC and LNS L2TP tunnel configurations.
If you do not configure the vpdn ip udp ignore checksum command, the L2TP software sends the packets to UDP to validate the checksum. When too many packets are queued to the IP input process, the router starts Selective Packet Discard (SPD) mechanism that causes IP packets to be dropped.
Note Head-of-the-line blocking of the IP input process might occur in other nonL2TP configurations. A flush occurring on an input interface indicates that the SPD mechanism is discarding packets.
When you use the lcp:interface-config RADIUS attribute to reconfigure the virtual access subscriber interface, call setup rate could be reduced on the Cisco ASR 1000 Series Aggregation Services Routers because the lcp:interface-config command syntax includes an IOS interface configuration command. This command is any valid IOS command that can be applied to an interface. When the lcp:interface-config attribute is downloaded from the RADIUS server to the Cisco ASR 1000 Series Aggregation Services Routers, the command parser is activated to configure the interface according to AV-pair, determining if the option is valid and then applying the configuration to the virtual access interface (VAI).
The subscriber session scaling on the Cisco ASR 1000 Series Aggregation Services Routers is not impacted by using the lcp:interface-config RADIUS attribute any more than if the equivalent IOS interface command was applied directly onto the virtual-template configuration and was cloned onto the VAI using that method. Using either the lcp:interface-config RADIUS attribute or the virtual-template to apply configuration onto the VAI it is the type of configuration being applied which may in a few cases affect the maximum subscriber session scale of the Cisco ASR 1000 Series Aggregation Services Routers.
To enhance scalability of per-user configurations without changing the router configuration, use the ip:vrf-id and ip:ip-unnumbered RADIUS attributes. These per-user vendor-specific attributes (VSAs) are used to map sessions to VRFs and IP unnumbered interfaces. The VSAs are applied to virtual access subinterfaces and are processed during PPP authorization.
The ip:vrf-id attribute is used to map sessions to VRFs. Any profile that uses the ip:vrf-id VSA must also use the ip:ip-unnumbered VSA to install IP configurations on the VAI that is to be created. The PPP that is used on a VAI to be created requires the ip:ip-unnumbered VSA. An Internet Protocol Control Protocol (IPCP) session is not established if IP is not configured on the interface. You must configure either the ip address command or the ip unnumbered command on the interface so that these configurations are present on the VAI that is to be created. However, specifying the ip address and ip unnumbered commands on a virtual template interface is not required because pre-existing IP configurations, if any, are removed when the ip:ip-vrf VSA is installed on the VAI. Therefore, any profile that uses the ip:vrf-id VSA must also use the ip:ip-unnumbered VSA to install IP configurations on the VAI that is to be created.
These per-user VSAs can be applied to VAIs. Therefore, the per-user authorization process does not require the creation of full VAIs, which improves scalability.
You should specify only one ip:vrf-id and one ip:ip-unnumbered value in a user profile. However, if the profile configuration includes multiple values, the Cisco ASR 1000 Series Aggregation Services Router applies the value of the last VSA received, and creates a virtual access subinterface. If the profile includes the lcp:interface-config VSA, the router always applies the value of the lcp:interface-config VSA.
You can specify one VSA value in a user profile on RADIUS and another value locally in the virtual template interface. The Cisco ASR 1000 Series Aggregation Services Router clones the template and then applies the values configured in the profiles it receives from RADIUS, resulting in the removal of any IP configurations when the router applies the profile values.
The requirement of a full virtual access interface when using the lcp:interface-config VSA in user profiles can result in scalability issues, such as increased memory consumption. This situation is especially true when the Cisco ASR 1000 Series Aggregation Services Router attempts to apply a large number of per-user profiles that include the lcp:interface-config VSA. Therefore, when updating your user profiles, we recommend that you redefine the lcp:interface-config VSA to the scalable ip:vrf-id and ip:ip-unnumbered VSAs.
The following example shows how to redefine the Loopback 0 interface using the ip:ip-unnumbered VSA.
Table 8-3 lists the features in this module and provides links to specific configuration information.
Note Table 8-3 lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.
In Cisco IOS XE Release 2.1S, this feature was introduced on the Cisco ASR 1000 Series Router.
In Cisco IOS XE Release 3.7S, this feature was introduced on the Cisco ASR 1000 Series Router.