web interface unreachable after firmware upgrade

[Rusver]

Recently, I upgraded the firmware on Cisco UCS C220 and C240 servers using the CIMC vKVM boot ISO method. While the upgrade process itself was straightforward, I encountered an issue where the CIMC web interface became inaccessible after the upgrade. However, SSH access to the CIMC was still available. Here’s how I tackled the issue and some troubleshooting steps that might help others facing the same problem.

Issue Description

During the firmware upgrade, the CIMC restarted as expected. However, after the reboot:

• The CIMC web interface was not accessible.

• SSH access was still functional.

• Running the following commands did not resolve the issue:

scope cimc

reboot  

show bios and show version reflect the cimc upgraded to the newer version.

what should I do?

[Steven Tardy]

What was the old CIMC version?
What is the new CIMC version?
Are you accessing CIMC from within the same VLAN?
Or accessing CIMC remotely? Is this remote connection over a VPN with a non-1500 MTU?

See: CSCwe22758 - After CIMC upgrade to 4.1(3b) and 4.2(2a) cannot access CIMC GUI and Intersight claim fails

[Rusver]

On C220 it was 4.0(4h) to 4.3(2.240053)
On C240 it was 4.1(2a) to 4.3(2.240053)
The CIMC worked before (I used it to Upgrade the firmware)
There is a VLAN for users and VLAN to Servers - it works on other server
No VPN. Ping and SSH to the upgraded CIMC works well.
I Can't get the login page on web on CIMC address...

[Elliot Dierksen]

Try closing all your browser sessions or a different browser. The CIMC may have changed/renewed the certificate, or changed some of the algorithms the web server supports. That could be annoying your browser.

[Steven Tardy · Accepted solution]

Somehow the CDET link I posted previously mysteriously pointed to the wrong CDET.
(Edited the prior post to link to the correct CDET, I think.)
Try the workaround from the CDET:

2) SSH to CIMC and change CIMC to allow some ICMP PMTU packets detailed in rfc1191:
scope cimc
scope network
show detail
scope icmp-configuration
set destination-unreachable-enabled yes
commit
show detail