How do I debug a large pause before network transactions when Network Manager is disabled?

Question

**Edited as I have narrowed the problem down a bit.

I have had a network problem since upgrading to 15.04 for which I have tried a new network card and clean installation of ubuntu, neither of which worked. My system was fine under 12.04 and 14.04. It is fine under 15.04 until I create a bridge.

When I have a network bridge enabled, there is a pause of up to about 30 seconds before a transaction starts, it is as if the network card is disabled or asleep.

In order to setup network taps, I changed my /etc/network/interfaces file to contain the following: # interfaces(5) file used by ifup(8) and ifdown(8) auto lo iface lo inet loopback

auto br0
iface br0 inet dhcp

pre-up tunctl -t tap0 -g tuntap
pre-up tunctl -t tap1 -g tuntap
pre-up ip link set dev eth0 down
pre-up brctl addbr br0
pre-up brctl addif br0 eth0
pre-up brctl addif br0 tap0
pre-up brctl addif br0 tap1
pre-up ip link set dev tap0 up
pre-up ip link set dev tap1 up
pre-up ip link set dev eth0 up
pre-up ip link set dev br0 up

up chmod 0666 /dev/net/tun

post-down ip link set dev eth0 down
post-down ip link set dev tap0 down
post-down ip link set dev tap1 down
post-down ip link set dev br0 down
post-down brctl delif br0 tap0
post-down brctl delif br0 tap1
post-down brctl delif br0 eth0
post-down brctl delbr br0

A bit of testing suggests it is the bridge setup which causes the problem rather than the taps.

With 12.04 and 14.04 I disabled network manager using: echo "manual" | sudo tee /etc/init/network-manager.override with 15.04 I found that I didn't need this.

I have tried two network cards, this is my lspci output for each:

For the Atheros I had to change the mtu to make it work with recent kernels

04:00.0 Ethernet controller: Qualcomm Atheros AR8161 Gigabit Ethernet (rev 08)
    Subsystem: Hewlett-Packard Company Device 2ad5
    Flags: bus master, fast devsel, latency 0, IRQ 32
    Memory at f7c00000 (64-bit, non-prefetchable) [size=256K]
    I/O ports at d000 [size=128]
    Capabilities: <access denied>
    Kernel driver in use: alx

I have tried both r8169 and r8168 drivers for the Realtek

02:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8411 PCI Express Gigabit Ethernet Controller (rev 06)
    Subsystem: Device 7470:3468
    Flags: bus master, fast devsel, latency 0, IRQ 27
    I/O ports at e000 [size=256]
    Memory at f7e00000 (64-bit, non-prefetchable) [size=4K]
    Memory at f0000000 (64-bit, prefetchable) [size=16K]
    Capabilities: <access denied>
    Kernel driver in use: r8169

Can anyone suggest anything else to try?

Thanks for any help

Tom

Answer 1

I found a different way of setting up the same thing, it uses some newer tools and fixed my problem on 15.04. My network interfaces file now looks like this:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

dns-search hh.imgtec.org

auto br1
iface br1 inet dhcp
   bridge_ports eth1 eth0
   bridge_stp on
   bridge_fd 0.0
   post-up ip tuntap add dev tap0 mode tap group tuntap
   post-up brctl addif br1 tap0
   post-up ifconfig tap0 up
   post-up ip tuntap add dev tap1 mode tap group tuntap
   post-up brctl addif br1 tap1
   post-up ifconfig tap1 up
   post-up ip tuntap add dev tap2 mode tap group tuntap
   post-up brctl addif br1 tap2
   post-up ifconfig tap2 up