I came across a host name resolution related issue when running SUM on an HEC project. Hope this blog finds you correctly if the same issue comes to you.
During SUM upgrade on HEC project I came across such error ‘Cannot find host in server list, please check SAP Note 129997’ on phase – MAIN_SHDIMP/SUBMOD_SHD2_RUN/RUN_RSPFROM_CRR_UPTIME.
Per Note 129997, It is crucial for the operation of the R/3 system that the following requirement is fulfilled for all hosts running R/3 instances:
a) The hostname of the computer (or the name that is configured with the profile parameter SAPLOCALHOST) must be resolveable into an IP address.
b) This IP address must resolve back into the same hostname. If the IP address resolves into more than one address, the hostname must be first in the list.
c) This resolution must be identical on all R/3 server machines that belong to the same R/3 system.
I checked the /etc/hosts file on OS level and find HEC has maintained multiple host names (2 different host names) for the same IP for app server. This is due to the management policy from both HEC side and customer side. (I would call them A for customer host name and B for HEC host name.)
For SUM tool, it will use the exact parameter which has been maintained in SAP default or instance profile (it is showing ‘host name A’). However in TX SM51 it will read the exact host name which is resolved by IP, which showing ‘host name B’. That is why the error comes.
Per note I executed niping -v -H <host name A> and get the result as following:
Lookup of hostname: A
–> IP – Addr: <IP 1>
Lookup of IP – Addr: <IP 1>
–> Hostname: B
We can see when we are resolving IP to hostname, it is resolved to B, which is not correct.
We all know the hosts resolution has a higher priority than DNS, so all I have done is transpose the sequence for the app server host name in /etc/hosts file. Let the host name A be the first place of all other names.
The result should looks like:
<IP1> <long host name A> <short host name A> <long host name B> <short host name B>
After changing, remember to restart the orig R/3 system and the shadow instance if you have and it still persists to make changes effective.
Then verify whether the host in SM51 turns to the correct one. And retry on SUM.
Hope this blog is helpful more or less.