Connect to server via SSH etc. works only after ping

SUSE Product Topics SLES Networking
1

Hi experts,

we are running several SLES 11 SP3 Enterprise Servers on VMs and they are all showing the same sitution:

  • System startup - OK
  • Connect to server with SSH Secure shell - Fail
  • Ping Server - OK
  • Connect to server with SSH Secure shell - OK
  • Working on Server using SSH for several minutes/hours … - OK
  • Trying to establish a new SSH connection after a few minutes - Fail
  • Ping Server - OK
  • Establish new SSH connection - OK

…

This isn’t only a SSH-Problem. On this machine a small SAP-System is installed which is showing
the same sitution when trying to connect using SAPGui.

  • Try to connect - fail
  • Ping Server - OK
  • Try to connect - OK
  • Working for several hours - OK
  • Trying to open a new SAPGui-Session after a few minutes - Fail
  • Ping Server - OK
  • New SAPGui-Session - OK

…

Working on the Machine using the Console of the VSphere-Client works without any problems.
All mounted network-drives etc are available without disconnects.

All machines have static IP adresses. IPv6 and the Linux Firewall is disabled. VMWare tools are also installed.

The network-connection of the ESX-Server hosting the systems is OK.
There are a few SLES10 servers on the same ESX working without any problems.

Any ideas what can cause these kind of problems ?

Thanks for your help

2

It’d probably be best if you could post a LAN trace, preferably of both
sides taken a the same time, showing the problem. For example:

sudo /usr/sbin/tcpdump -n -s 0 -i any -w /tmp/lan.cap

While running that on both sides, do the test as described below, then
post the resulting /tmp/lan.cap file somewhere for review. While getting
the data from one side only may be helpful, having both is really the best
way.

The problem kind of sounds like an ARP issue. Having the firewall
shouldn’t matter, and generally speaking it should be up so that may be
worth doing (after allowing desirable services like SSH and SAP), but
either way should work.

Perhaps post the output of the following from the client and server sides
before and after fixing the issue:

ip neigh

–
Good luck.

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