Effective from Cisco IOS XE Release
3.10S, the per-session Stateful Switchover (SSO)/In Service Software Upgrade
(ISSU) feature supports iWAG mobility sessions that are tunneled to MNO using
GTP. The SSO feature takes advantage of Route Processor (RP) redundancy by
establishing one of the RPs as the active processor, while the other RP is
designated as the standby processor, and then synchronizing the critical state
information between them. When a failover occurs, the standby device seamlessly
takes over, starts performing traffic-forwarding services, and maintains a
dynamic routing table.
Your software release may not support all the features documented in
this module. For the latest caveats and feature information, see
Bug Search Tool and 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 table at the end
of this module.
Use Cisco Feature Navigator to find information about platform support
and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/go/cfn. An account on
Cisco.com is not required.
iWAG SSO Support for GTP
The SSO/ISSU feature
supports only the Cisco ASR 1000 Series Aggregation Services Routers
intrachassis (RP-to-RP) SSO, but not the interchassis (Cisco ASR1K-to-Cisco
ASR1K) SSO. The First Sign Of Life (FSOL) triggers that are supported on SSO
include DHCP proxy (where the iWAG acts as the DHCP proxy server) and DHCP
proxy plus unclassified MAC.
The process as part
of iWAG SSO handling GTP checkpoints to the standby RP the information that is
necessary to create a copy of the session on the standby RP. Such an inactive
copy of the session becomes active when the standby RP becomes active.
When an iWAG
mobility session with GTP tunneling is enabled using the SSO/ISSU feature, the
Cluster Control Manager on the active RP needs to wait for a few more
components, including the GTP, to become ready before checkpoint data
collection, and polls these additional components for checkpoint data during
data collection. A very similar operation is performed on the standby RP as
well. Although such additional CPU consumption is per session, it is not
expected to be too heavy since processing in each of these components should
include the time spent on a few data structure lookups and memory-copying
During ISSU SIP and
SPA upgrade, there is traffic interruption. To avoid session disconnect because
of dropped echo messages during such traffic interruption, a user has the
Option 1 (preferred):
Disable the echo messages
on the iWAG and GGSN for the duration of the ISSU.
Re-enable the echo messages
after ISSU is completed on the iWAG and GGSN.
Option 2: Extend the t3 and
n3 configurations to exceed the expected traffic interruption. The traffic
interruption characterized in the Cisco IOS XE Release 3.10S is 127 seconds.
Hence, we recommend the following t3 and n3 settings (t3_response: 1 and
n3_request: 7, resulting in 127 seconds on both the iWAG and GGSN) but the
duration of the traffic interruption may depend on the types of SIPs and SPAs
and how loaded the router is. If traffic interruption exceeds the configured t3
and n3 limits, the session is disconnected.
Support for the GTP
This section describes how to
enable SSO support for the GTP on the Cisco ASR 1000 Series Aggregation
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The following table provides release information about the feature or features described in this module. This table 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.
Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to
www.cisco.com/go/cfn. An account on Cisco.com is not required.
Table 1 Feature Information
for iWAG SSO Support for GTP
iWAG SSO Support for GTP
Cisco IOS XE Release 3.10
In Cisco IOS XE Release 3.10S, this feature was implemented on
the Cisco ASR 1000 Series Aggregation Services Routers.
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