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    Application Support for Unified ISSU

    When an application supports unified ISSU, you can configure the application on the router and proceed with the unified in-service software upgrade with no adverse impact to the upgrade.

    Applications that do not support unified ISSU cannot maintain state and configuration with minimal traffic loss across the upgrade. When you attempt the unified in-service software upgrade on a router that is configured with an ISSU-challenged application, the unified in-service software upgrade is halted and cannot proceed unless you remove the configuration. An application that does not support high availability cannot support unified ISSU.

    Table 1 indicates which applications support or do not support a unified in-service software upgrade, as well as limitations on their behavior.

    Table 1: Application Support for Unified In-Service Software Upgrades





    Physical Layer Protocols

    (E120 and E320)





    Unified ISSU support is provided only for non-channelized APS IOAs. Also, unified ISSU can proceed only if you have not configured APS on the OCx/STMx ATM or OCx/STMx POS line modules. If you have configured APS, a warning message is displayed and the router cannot proceed with the unified ISSU.

    The unified ISSU process for channelized line modules remains unchanged.

    E120 and E320 routers do not support APS.


    Link-Layer Protocols


    ARP entries in the ARP cache do not time out because no ARP aging occurs during unified ISSU. When the unified ISSU is completed, the ARP cache contains the same entries as it had before the unified ISSU began.


    ATM 1483 bulk configuration of dynamic interfaces

    ATM bulk configuration of static interfaces

    Bridged Ethernet

    Cisco HDLC

    Ethernet (with and without VLANs)

    Frame Relay



    Transparent bridging

    Unicast Routing

    Access Routes



    Although unified ISSU supports FTP in active state, no file transfer operation can be in progress while performing unified ISSU.



    IPv6 is unified ISSU safe and compliant.

    Unified ISSU is not supported for IPv6 configurations and IPv6-related applications that are not supported for the IPv6 high availability feature.

    IPsec Transport
    (E120 and E320)

    E120 and E320 routers do not support IPsec.

    IPsec Transport

    IPsec Tunnels
    (E120 and E320)

    E120 and E320 routers do not support IPsec.

    IPsec Tunnels


    Support only when graceful restart is configured.


    Support only when graceful restart is configured.


    Support only when graceful restart is configured.


    Support only when graceful restart is configured.


    Static Routes


    Authentication and command authorizations on Telnet sessions fail during the upgrade phase and Telnet sessions are dropped.

    IPv4 Multicast Routing

    Multicast Routing

    ANCP (L2C)

    Unified ISSU can proceed if ANCP is configured. However, ANCP has no graceful restart extensions and therefore it cannot maintain its dynamic state across the upgrade. Consequently, all ANCP sessions are brought down and then restored when the upgrade is completed.

    (E120 and E320)




    IPv6 Multicast Routing


    Multicast Routing

    IPv6 routing protocols are unified ISSU safe, but do not support ISSU.


    IPv6 routing protocols are unified ISSU safe, but do not support ISSU.


    IPv6 routing protocols are unified ISSU safe, but do not support ISSU.

    Multiprotocol Label Switching


    BGP signaling

    Unified ISSU supports BGP IPv6 address families. For more information about unified ISSU support, see IPv6 BGP Behavior During Unified ISSU.

    LDP signaling

    RSVP-TE signaling

    Local cross-connects between layer 2 interfaces using MPLS

    Policies and QoS




    Remote Access


    The following configuration is not supported: The subscriber username and password are on an ATM circuit in Bridged Ethernet over ATM or IP over ATM configurations.

    DHCP External Server and Packet Trigger

    DHCP Packet Capture

    Configuration of DHCP packet capture does not prevent unified ISSU from proceeding. However, the capturing of packets on the line modules is halted when the unified ISSU upgrade phase commences. Packet capture resumes automatically during the unified ISSU service restoration phase.

    DHCP Proxy Client

    DHCP Relay Proxy

    DHCP relay proxy continues processing of DHCP release requests during the unified ISSU to maintain server-client synchronization. State is preserved across the upgrade; statistics are not preserved.

    DHCP Relay Server

    DHCPv4 Local Server

    Forwarding outages that take place during a unified ISSU can affect DHCP lease renewal. Before you begin unified ISSU, we recommend that you configure the DHCP local server address pools with a minimum lease time of 120 minutes to ensure that leases do not expire during the upgrade.

    DHCPv6 Local Server

    IPv6 is ISSU safe and compliant. You can upgrade ISSU when DHCPv6 local server applications are configured. However, during the ISSU upgrade, new requests for IPv6 prefixes are blocked by the DHCPv6 local server.


    Unified ISSU forces an L2TP failover for all established tunnels. L2TP failover resynchronization is required for successful recovery of a tunnel and its sessions following the upgrade.

    L2TP Dialout

    IPv4 Local Address Pools

    IPv6 Local Address Pools

    IPv6 is ISSU safe and compliant. You can upgrade ISSU when IPv6 local address pool applications are configured on the server.

    Local Authentication Server

    RADIUS Client

    RADIUS Dynamic-Request Server

    RADIUS Initiated Disconnect

    RADIUS Relay Server

    RADIUS Route-Download Server

    SRC Client

    Service Manager

    Subscriber Manager



    Bulk statistics

    Denial of Service (DoS) protection

    HTTP server

    IOA hot swap

    J-Flow (IP flow statistics)

    Line Module Redundancy

    You can use the active spare line module for unified ISSU operations. You do not have to revert to the primary line module. The following sets of line modules and IOAs are supported:

    • ATM: OC3-4A, OC3/OC12/DS3-ATM
    • POS: OC3-4P
    • Line Modules
      • ES2 4G LM
      • ES2 10G Uplink LM
      • ES2 10G LM
      • ES2 10G ADV LM
    • IOAs
      • ES2-S1 GE-4 IOA
      • ES2-S1 GE-8 IOA
      • ES2-S3 GE-20 IOA
      • ES2-S1 10GE IOA
      • ES2-S2 10GE PR IOA
      • ES2-S1 OC3-8 STM1 ATM IOA
      • ES2-S1 OC12-2 STM4 ATM IOA
      • ES2-S1 OC12-2 STM4 POS IOA
      • ES2-S1 OC48 STM16 POS IOA

    Mobile IP Home Agent

    Network Address Translation (NAT)

    You must remove the NAT license configuration as well as the NAT configuration from the router.


    Resource Threshold Monitor

    Response Time Reporter

    Route Policy


    Subscriber Interfaces

    Tunnels (GRE and DVMRP)


    Published: 2014-08-12