A useful comment about a networking issue with Xen. Something I’ll have to try out at some point.
On a separate but still networking issue, I noticed that my XenU’s outbound traffic is sporadic (between 800KB/sec and 2MB/sec). The problem is the default qdisc being inadequate. So I fix it with:
XenU# tc qdisc add dev eth0 root tbf rate 50mbit latency 20ms burst 50k
TBF requires kernel option CONFIG_NET_SCH_TBF, but other qdisc should work too if the buffer is large enough to handle the bandwidth. To make this permanent, add it as a ‘up’ line to iface eth0 in XenU’s /etc/network/interfaces.