During the building and configuration of a number of brand spanking new Cisco 6509’s with Sup720-3C I decided to convert them to VSS mode before updating the IOS (mainly due to laziness and only having console access). The conversion worked a treat however when I can to upgrade the IOS with ISSU I seemed to hit a glitch, the standby sup got itself in a reboot loop.

The error messages seen;

*Jul 26 14:38:21.291: %PFREDUN-SW1_SP-4-PHYSMEM_MISMATCH: Asymmetrical redundant configuration: Active SP has (1048576/8192K) memory, Standby has (1048576/65536K).
*Jul 26 14:38:21.291: %PFREDUN-SW1_SP-4-PHYSMEM_MISMATCH: Asymmetrical redundant configuration: Active RP has (1048576/8192K) memory, Standby has (1048576/65536K).
*Jul 26 14:38:22.307: %PFREDUN-SW1_SP-6-ACTIVE: Standby initializing for RPR mode
*Jul 26 14:38:23.856: %ISSU-SW1_SP-3-FSM_MISMATCH_MTU: ISSU nego failed for client ISSU ifs client(110) entity_id 113 session 393699 due to mismatch of mtu size 72 & 36. : ios-base : (PID=12311, TID=17) : -Traceback=(s72033-advipservicesk9_wan-5-dso-bnp.so+0x94088) ([27:-3]4-dso-b+0x1ED79C) ([37:0]+0x1ED81C) ([27:-3]5-dso-bnp+0x908A4) ([39:0]+0x90B70) ([39:0]+0x91090) ([27:-3]6-dso-b+0x136110) ([27:-9]3+0x39F400) ([37:0]+0x36BF88) ([27:-9]7+0x1AA8A0) ([37:0]+0x1AA878)
*Jul 26 14:38:23.892: %ISSU-SW1_SP-4-FSM_INCOMP: Version of local ISSU client ISSU ifs client(110) in session 393699 is incompatible with remote side.
*Jul 26 14:38:23.892: %RFS-SW1_SP-3-START_NEGO_SESSION: RFS nego (393699:590199) to [issu:rfs:Secondary RFS Server Port:0x4050000] failed: [ISSU_RC_NEGO_ERROR]

After trying a couple of things (and not having patience) I decided to break out into ROMMON and reload with config-register of 0x2142 so that I could stop the roboot loop and put VSS into standalone mode. Although this worked a treat and I had both 6500 in standalone mode and with blank configuration (wr erase) I was unable to do anything on upgradeing the image as ISSU seemed to get stuck in it upgrade process;

Router#sh issu state detail
                          Slot = 5
                      RP State = Active
                    ISSU State = System Reset
                 Boot Variable = bootdisk:s72033-advipservicesk9_wan-vz.122-33.S
XI2a.bin,12;
                Operating Mode = sso
               Primary Version = bootdisk:s72033-advipservicesk9_wan-vz.122-33.S
XI2a.bin
             Secondary Version = bootdisk:s72033-advipservicesk9_wan-vz.122-33.S
XI2a.bin
               Current Version = bootdisk:s72033-advipservicesk9_wan-vz.122-33.S
XI2a.bin
                Variable Store = PrstVbl
% Standby information is not available because it is in 'DISABLED' state

 

Router(config)#boot system flash sup-bootdisk:s72033-advipservicesk9_wan-vz.122-33.SXI2a.bin
% ISSU process is in progress; Boot variable can not be updated.

 

Router#issu abortversion
The system is without a fully initialized peer and Service impact will occur. Pr
oceed with abort? [confirm]
% ISSU process can be aborted only from [ Load Version ] or [ Run Version ] or [
 Load Version - Switchover ] or [ Run Version - Switchover ] state

After trying a couple of command and looking on google I was no closer to getting the box back in a state that I could do anything with….until it dawned on me “I wonder if a clear command exists for ISSU to reset the flag”. Well yes it does;

Router#clear issu state
 
Router#sh issu state detail
                          Slot = 5
                      RP State = Active
                    ISSU State = Init
                 Boot Variable = bootdisk:s72033-advipservicesk9_wan-vz.122-33.S
XI2a.bin,12;
                Operating Mode = sso
               Primary Version = N/A
             Secondary Version = N/A
               Current Version = bootdisk:s72033-advipservicesk9_wan-vz.122-33.S
XI2a.bin
                Variable Store = PrstVbl
% Standby information is not available because it is in 'DISABLED' state

Once I put the config-register back and added the required boot statement I was at a point in which I can re-convert the VSS.