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Here is a quick summary of the issue. I cannot communicate with a linux network namespace within the same subnet. I am running Ubuntu 14.04.1 LTS on a headless server. I have been troubleshooting this for about a week, so thanks in advanced for any response.

From the beginning: (tcpdump at the bottom)

I have two physical interfaces em1 and em2. I've created two bridges br0 and br1. The first bridge br0 contains my external interface em1. The second bridge br1 contains my internal interface em2, and veth0(which is linked to veth1 in a network namespace named vpn as shown below.)

cat /etc/network/interfaces

# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback

# Bridge setup
auto br0 em1
iface br0 inet dhcp
bridge_ports em1

auto br1 em2 veth0
iface br1 inet static
address 10.0.0.1
network 10.0.0.0
netmask 255.255.255.0
broadcast 10.0.0.255
bridge_ports em2 veth0

# pre and post up
pre-up ip link add name veth0 type veth peer name veth1
pre-up ip netns add vpn
pre-up ip link set veth1 netns vpn
post-up ip netns exec vpn ip link set dev lo up
post-up ip netns exec vpn ip link set dev veth1 up
post-up ip netns exec vpn ip addr add 10.0.0.254/24 broadcast 10.0.0.255 dev veth1
post-up ip netns exec vpn ip route add default via 10.0.0.1

I am using this server for routing. Here is my nat.sh, which runs every boot.

echo -e "\n\nLoading simple rc.firewall-iptables version $FWVER..\n"
DEPMOD=/sbin/depmod
MODPROBE=/sbin/modprobe

EXTIF="br0"
INTIF="br1"
#INTIF2="eth0"
echo "   External Interface:  $EXTIF"
echo "   Internal Interface:  $INTIF"

#======================================================================
#== No editing beyond this line is required for initial MASQ testing == 
echo -en "   loading modules: "
echo "  - Verifying that all kernel modules are ok"
$DEPMOD -a
echo "----------------------------------------------------------------------"
echo -en "ip_tables, "
$MODPROBE ip_tables
echo -en "nf_conntrack, " 
$MODPROBE nf_conntrack
echo -en "nf_conntrack_ftp, " 
$MODPROBE nf_conntrack_ftp
echo -en "nf_conntrack_irc, " 
$MODPROBE nf_conntrack_irc
echo -en "iptable_nat, "
$MODPROBE iptable_nat
echo -en "nf_nat_ftp, "
$MODPROBE nf_nat_ftp
echo "----------------------------------------------------------------------"
echo -e "   Done loading modules.\n"
echo "   Enabling forwarding.."
echo "1" > /proc/sys/net/ipv4/ip_forward
echo "   Enabling DynamicAddr.."
echo "1" > /proc/sys/net/ipv4/ip_dynaddr 
echo "   Clearing any existing rules and setting default policy.."

iptables-restore <<-EOF
*nat
-A POSTROUTING -o "$EXTIF" -j MASQUERADE
COMMIT
*filter
:INPUT ACCEPT [0:0]
:FORWARD DROP [0:0]
:OUTPUT ACCEPT [0:0]
-A FORWARD -i "$EXTIF" -o "$INTIF" -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT 
-A FORWARD -i "$INTIF" -o "$EXTIF" -j ACCEPT
-A FORWARD -j LOG
COMMIT
EOF

echo -e "\nrc.firewall-iptables v$FWVER done.\n"

All the devices on the network have addresses from this server, and are on the same subnet. Everything is communicating perfectly with each other. My only problem is that none of the devices can reach veth1 inside the network namespace vpn, even though it has an address and subnet from the server like everything else, and can even ping google.

For example from my laptop with the address of 10.0.0.4. The command ping 10.0.0.1 works, and ping 10.0.0.3(My Xbox) works. But ping 10.0.0.254 does not work, even though it is on the same network as everything else.

Here is some additional information:

sysctl net.ipv4.ip_forward

net.ipv4.ip_forward = 1

cat /proc/sys/net/ipv4/ip_forward

1

ifconfig

br0       Link encap:Ethernet  HWaddr 00:1e:67:ad:9e:1d  
          inet addr:71.95.217.302  Bcast:255.255.255.255  Mask:255.255.254.0
          inet6 addr: fe80::21e:67ff:fead:9e1d/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:57249 errors:0 dropped:0 overruns:0 frame:0
          TX packets:17297 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:13724815 (13.7 MB)  TX bytes:2606039 (2.6 MB)

br1       Link encap:Ethernet  HWaddr 00:1e:67:ad:9e:1e  
          inet addr:10.0.0.1  Bcast:10.0.0.255  Mask:255.255.255.0
          inet6 addr: fe80::21e:67ff:fead:9e1e/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:17716 errors:0 dropped:0 overruns:0 frame:0
          TX packets:18625 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:2382424 (2.3 MB)  TX bytes:11990075 (11.9 MB)

em1       Link encap:Ethernet  HWaddr 00:1e:67:ad:9e:1d  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:58804 errors:0 dropped:0 overruns:0 frame:0
          TX packets:17304 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:14632304 (14.6 MB)  TX bytes:2606465 (2.6 MB)
          Memory:b1200000-b1280000 

em2       Link encap:Ethernet  HWaddr 00:1e:67:ad:9e:1e  
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:17636 errors:0 dropped:0 overruns:0 frame:0
          TX packets:20125 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:2639201 (2.6 MB)  TX bytes:12086082 (12.0 MB)
          Memory:b1100000-b1180000 

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:65536  Metric:1
          RX packets:4775 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4775 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:939016 (939.0 KB)  TX bytes:939016 (939.0 KB)

veth0     Link encap:Ethernet  HWaddr 4e:99:98:cc:48:6d  
          inet6 addr: fe80::4c99:98ff:fecc:486d/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:75 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1902 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:6799 (6.7 KB)  TX bytes:140261 (140.2 KB)

brctl show br0

bridge name     bridge id           STP enabled   interfaces
br0             8000.001e67ad9e1d   no            em1

brctl show br1

bridge name     bridge id           STP enabled   interfaces
br1             8000.001e67ad9e1e   no            em2
                                                  veth0

ip route

default via 71.95.216.1 dev br0 
10.0.0.0/24 dev br1  proto kernel  scope link  src 10.0.0.1 
71.95.216.0/23 dev br0  proto kernel  scope link  src 71.95.217.302

route

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use  Iface
default         71-95-216-1.sta 0.0.0.0         UG    0      0        0  br0
10.0.0.0        *               255.255.255.0   U     0      0        0  br1
71.95.216.0     *               255.255.254.0   U     0      0        0  br0

ip netns exec vpn ifconfig

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:65536  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)

veth1     Link encap:Ethernet  HWaddr 3e:0a:b5:c6:f4:07  
          inet addr:10.0.0.254  Bcast:10.0.0.255  Mask:255.255.255.0
          inet6 addr: fe80::3c0a:b5ff:fec6:f407/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:1987 errors:0 dropped:0 overruns:0 frame:0
          TX packets:75 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:146530 (146.5 KB)  TX bytes:6799 (6.7 KB)

ip netns exec vpn ip route

default via 10.0.0.1 dev veth1 
10.0.0.0/24 dev veth1  proto kernel  scope link  src 10.0.0.254

ip netns exec vpn route

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use  Iface
default         10.0.0.1        0.0.0.0         UG    0      0        0  veth1
10.0.0.0        *               255.255.255.0   U     0      0        0  veth1

I did a ping 10.0.0.254 from 10.0.0.4 while running a tcpdump -v -i br1 > file then greped the tcpdump output file for 10.0.0.254. You can view the entire tcpdump (which is not long) here http://pastebin.com/raw.php?i=Rs9dpw4V.

21:07:55.648413 ARP, Ethernet (len 6), IPv4 (len 4), Request who-has 10.0.0.254 tell 10.0.0.4, length 46
21:07:55.648448 ARP, Ethernet (len 6), IPv4 (len 4), Reply 10.0.0.254 is-at 3e:0a:b5:c6:f4:07 (oui Unknown), length 28
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 0, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 1, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 2, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 3, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 4, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 5, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 6, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 7, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 8, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 9, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 10, length 64
    10.0.0.4 > 10.0.0.254: ICMP echo request, id 11630, seq 11, length 64

If there is any missing information, please let me know.

EDIT:

iptables -L -nv

Chain INPUT (policy ACCEPT 33M packets, 45G bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain FORWARD (policy DROP 17439 packets, 3112K bytes)
 pkts bytes target     prot opt in     out     source               destination         
2640K 3411M ACCEPT     all  --  br0    br1     0.0.0.0/0            0.0.0.0/0            ctstate RELATED,ESTABLISHED
2470K  464M ACCEPT     all  --  br1    br0     0.0.0.0/0            0.0.0.0/0           
17439 3112K LOG        all  --  *      *       0.0.0.0/0            0.0.0.0/0            LOG flags 0 level 4

Chain OUTPUT (policy ACCEPT 21M packets, 35G bytes)
 pkts bytes target     prot opt in     out     source               destination

iptables -t nat -L -nv

Chain PREROUTING (policy ACCEPT 280K packets, 30M bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain INPUT (policy ACCEPT 187K packets, 22M bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain OUTPUT (policy ACCEPT 198K packets, 13M bytes)
 pkts bytes target     prot opt in     out     source               destination         

Chain POSTROUTING (policy ACCEPT 58488 packets, 3569K bytes)
 pkts bytes target     prot opt in     out     source               destination         
 222K   15M MASQUERADE  all  --  *      br0     0.0.0.0/0            0.0.0.0/0

ip netns exec vpn arping -I veth1 -c 3 10.0.0.2

ARPING 10.0.0.2
60 bytes from 90:72:40:05:79:87 (10.0.0.2): index=0 time=1.001 sec
60 bytes from 90:72:40:05:79:87 (10.0.0.2): index=1 time=1.001 sec
60 bytes from 90:72:40:05:79:87 (10.0.0.2): index=2 time=1.001 sec

--- 10.0.0.2 statistics ---

arping -I br1 -c 3 10.0.0.254

ARPING 10.0.0.254
42 bytes from 3e:0a:b5:c6:f4:07 (10.0.0.254): index=0 time=1.001 sec
42 bytes from 3e:0a:b5:c6:f4:07 (10.0.0.254): index=1 time=1.001 sec
42 bytes from 3e:0a:b5:c6:f4:07 (10.0.0.254): index=2 time=1.001 sec

--- 10.0.0.254 statistics ---
3 packets transmitted, 3 packets received,   0% unanswered (0 extra)
  • You logged (and dropped) quite a bit of forwarded traffic. You should look at those logs. – Michael Hampton May 29 '15 at 15:48
  • @MichalSokolowski I have run the two commands you have requested (iptables -L -nv & iptables -t nat -L -nv). They are now at the bottom of the question. Thank You! – David Custer May 29 '15 at 15:52
  • @MichaelHampton I've edited my post to include a pastebin link to the entire tcpdump log file I created (which is not long at all). Here it is for easy access if you wish to look at it. pastebin.com/raw.php?i=Rs9dpw4V – David Custer May 29 '15 at 16:00
  • Try arping if you get any response. – kenorb May 29 '15 at 16:31
  • @kenorb Toward the bottom of the post I pinged it, and recored the data in a tcpdump. – David Custer May 29 '15 at 21:43
1

I'm going to assume if you do sudo iptables -L | grep policy it will look something like this:

Chain INPUT (policy ACCEPT)
Chain FORWARD (policy DROP)
Chain OUTPUT (policy ACCEPT)

If you simply do iptables --policy FORWARD ACCEPT. Your issue will be resolved. But having a server without setting iptables correctly can be dangerous. So you will probably want to refer to this wonderful guide to get yourself started using iptables.

  • Would a forward rule from br1 to veth1 have accomplished the same as changing the forwarding policy to ACCEPT? – rjt May 30 '15 at 14:49
  • @rjt No idea. I'll test that when I get home, and get back with you. – David Custer May 30 '15 at 16:25

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