I am currently building my first production ready (well non-production really) XenServer cluster and ran into this issue when attempting to add my second host into the cluster. I hit google and found out that this was actually just a dns issue.
A quick check on the /etc/resolv.conf on two of my nodes, shows nothing but the following line.
; generated by /etc/sysconfig/network-scripts/ifup-post
Well great, on a standard linux box I would have just added my name server and would have been half way to the bar, but judging by the contents of the resolv.conf I figured that I was supposed to add it another way.
Well after a bit of poking around in XenCenter I found this. Click on the hostname of the XenServer, then click on the "Networking" tab, from there click on "Configure…" below the "Management Interfaces" section as illustrated below. You will then be presented with a pop-up window where you can enter your nameservers.
Note that you can also do this from the command line, however you have to go basically reconfigure your management interface.. ip, gateway, and everything that goes with it.
First run the command below
#xe pif-list host-name-label=xen01 management=true
Then using the UUID of the management interface, run the command below. Replace my IP addresses and uuid with yours.
#xe pif-reconfigure-ip mode=static IP=10.120.72.11 uuid=dc6b6651-6067-9a52-2011-6ba102da39e1 DNS=10.120.69.1 netmask=255.255.255.0 gateway=10.120.72.1
Seeing how fickle XenServer Clustering is regarding DNS, its probably not a bad idea to add /etc/host entries on your XenServer nodes for each server that will be in your cluster. You never know when dns might go out to lunch and you don't want your HA cluster affected.
For future reference you can check all the configuration parameters of your management interface with the following commands.
First get the UUID of your management interface.
xe pif-list management=true host-name-label=xen01
Then check the configuration via the UUID.
xe pif-param-list uuid=f61b8d4d-67ec-e262-3e16-4348baaed076
And for example if you need to configure the DNS search domain, you can run the following.
xe pif-param set uuid=f61b8d4d-67ec-e262-3e16-4348baaed076 other-config:domain=MYDOMAIN