Xenserver guest OS network configuration

I am presently able to ping the guest OS' (for example, I can tell because they stop pinging when the guest VMs are powered down or the network is being restarted, etc.), but none of them can ping out or perform any network tasks.

The inbound ping started responding after configuring IP forwarding and setting up the xenbr0 per http://www.jansipke.nl/using-xenserver-in-a-routed-ip-network/ and moving the VMs to the other NIC (Guest VM on XenServer unable to reach network), however, the VMs cannot ping out or reach any sort of outside connection less the gateway (the host IP), despite being able to ping in.

Is this more likely as issue on the guest OS-level, or with the network configuration of the host? I am inclined to say the former because I can ping in to the IP from outside the Xenserver's network.

Guest tools, etc. have been installed, as far as I can tell, there is no firewall issue occurring.

The guest OSes that are affected are Ubuntu 12.04 (which gets the unknown instance error, usually a /etc/udev/rules.d/… issue on VPS, but seems not to be the case here) and CentOS 6.3 neither of which have firewalls enabled:

The eth0 configuration for the CentOS VM is:

DEVICE="eth0"
BOOTPROTO="none"
DEVICE="eth0"
BOOTPROTO="none"
HWADDR="32:E8:7F:43:CF:5F"
NM_CONTROLLED="yes"
ONBOOT="yes"
TYPE="Ethernet"
UUID="a137f23c-cf18-4bb5-beb5-38ff76371363"
IPADDR="174.34.135.164"
NETMASK="255.255.255.192"
GATEWAY="174.34.135.162" [The host IP]

[root@localhost ~]# route
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
174.34.135.128  *               255.255.255.192 U     0      0        0 eth0
link-local      *               255.255.0.0     U     1002   0        0 eth0
default         174.34.135.162  0.0.0.0         UG    0      0        0 eth0

[root@localhost ~]# ifconfig -a
eth0      Link encap:Ethernet  HWaddr 32:E8:7F:43:CF:5F  
          inet addr:174.34.135.164  Bcast:174.34.135.191  Mask:255.255.255.192
          inet6 addr: fe80::30e8:7fff:fe43:cf5f/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:206999 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1678 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:9606174 (9.1 MiB)  TX bytes:91721 (89.5 KiB)
          Interrupt:246 

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:10 errors:0 dropped:0 overruns:0 frame:0
          TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:616 (616.0 b)  TX bytes:616 (616.0 b)

Both can hit the gateway and the resolver IPs (8.8.8.8, etc.) but cannot resolve hostnames and hit other IPs that are not in the network configuration.

The XenServer configuration may not be relevant, given that incoming ping to the Guest OS IP works and networking on the host seems to be working properly, but in any case:

    [root@srv240 ~]# ifconfig |grep -A 6 "eth\|xenbr"
eth0      Link encap:Ethernet  HWaddr 00:17:31:73:40:58  
          UP BROADCAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
          Interrupt:17 
--
eth1      Link encap:Ethernet  HWaddr 00:18:F3:63:2B:14  
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:347427 errors:0 dropped:0 overruns:0 frame:0
          TX packets:160203 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:23706160 (22.6 MiB)  TX bytes:203615293 (194.1 MiB)
          Interrupt:16 
--
xenbr0    Link encap:Ethernet  HWaddr 00:17:31:73:40:58  
          inet addr:174.34.135.162  Bcast:174.34.135.167  Mask:255.255.255.248
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)
--
xenbr1    Link encap:Ethernet  HWaddr 00:18:F3:63:2B:14  
          inet addr:174.34.135.162  Bcast:174.34.135.167  Mask:255.255.255.248
          UP BROADCAST RUNNING PROMISC MULTICAST  MTU:1500  Metric:1
          RX packets:343907 errors:0 dropped:0 overruns:0 frame:0
          TX packets:43867 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:22104935 (21.0 MiB)  TX bytes:196685281 (187.5 MiB)