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[Xen-users] No dom0/domU ping "out of the box"

Sorry if this is covered somewhere else in the archives, but I don't see
a case that has symptoms that match my case.

I installed Xen 3 in a pretty-close-to-vanilla Debian bootstrap.  Using
the default Xen configuration (network-route and vif-route), I cannot
get ping to work in either direction between a domU and dom0.  Both
sides report "Destination Host Unreachable".  

Domain config params (among others):
  ip     = ""  
  gateway= ""
  netmask= ""
  vif = [ '' ]
  dhcp   = "off"

On dom0, ifconfig reports presence of eth0, lo, vif4.0 and xenbr0.  I
see no signs of the peth0 or vif0.0 interfaces mentioned in the
XenNetworking wiki article.  A brctl on xenbr0 reveals only one
interface on xenbr0 (vif4.0).  So, what happened to peth0 and vif0.0? 
How do I investigate further?

I want to identify dom0 to the domUs as, so (and I'm working
out of ignorance here) I set the ip address on vif4.0 to
under the assumption that the "virtual crossover cable" between eth0 on
domain 4 and vif4.0 on dom0 is the moral equivalant of a cable between
two physical machines.  Am I close here?

On domU (domain 4), ifconfig reveals lo and eth0, the latter having the
correct ip address,

However, pings from either vm to the other's ip address fail with
"Destination Host Unreachable".  Yet I do see appropriate TX and RX
packet counts in eth0 in domU and vif4.0 in dom0.

Pings to do work on both machines.

Suspecting routing/filtering issues, I checked that iptables on either
machine reports accept policy for all filtering tables and no other
entries.  And route reports what seem to be reasonable routing:

 - on domU: UH    0      0        0
eth0   U     0      0        0
eth0         UG    0      0        0

- on dom0 UH    0      0        0
vif4.0   U     0      0        0
vif4.0   U     0      0        0
eth0         UG    0      0        0

The 69.165.xxx is my ISP dynamically-assigned stuff.  (I'm not
interested in the domUs having access to the ISP.)

Those route entries, by the way, may not be exactly how they were
automatically set up since I've been fiddling a bit and don't recall if
I did any route changes that I didn't undo.

I'm guessing that my boot scripts in either dom0 or domU or both are
doing some hidden mucking with networking that I'm not seeing -- the
world of Linux networking is new to me, as you can probably tell.  I
think I understand what I know but I think there is lots I'm not aware

So I end with these questions:
1. Where do I look from here?
2. What are the possible causes of "Destination Host Unreachable"?
3. Why doesn't the bridge look like the wiki article XenNetworking
describes so nicely?
4. Is my guess of setting the dom0 ip address on vif4.0 in anywhere near
the right direction?
5. If not, how should I set things up if my primary ip address on dom0
is dynamically assigned by my ISP and I want my domUs to have static
addresses and static addresses for their gateway?

Thanks in advance,

Colin Brown
CIS -- Franklin University

Colin William Brown (Bill)
Visiting Professor -- Computer Science
Franklin University


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