Linux network namespaces - ping fails on specific veth
Well, first of all, you have two "logically" seperate virtual ethernet networks.
on veth-b use 10.0.2.1/24 and use 10.0.2.4/24 on veth-2
on veth-a use 10.0.1.1/24 and use 10.0.1.3/24 on veth-1
veth-b and veth-2 are a different network to veth-a and veth-1, so you ought to give them seperate IP subnets.
You still won't be able to ping from 10.0.1.3 to 10.0.2.4 unless you do:
$ echo 1 > /proc/sys/net/ipv4/ip_forward
$ sudo ip netns exec nstest2 ip route add default via 10.0.2.1
$ sudo ip netns exec nstest1 ip route add default via 10.0.1.1
Good Luck!
Vasilis
Updated on September 18, 2022Comments
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Vasilis almost 2 years
I just started to exploring network namespaces. I try to implement the following simple setting following the article in http://www.opencloudblog.com/?p=42
+--------+ +-----------+ +--------+ | |------+ +------+ |------+ +------| | |nstest2 |veth-2++------++veth-b| Default |veth-a++------++veth-1| nstest1| | |------+ +------+ namespace |------+ +------| | +--------+ +-----------+ +--------+
I execute the following commands:
#setup namespace nstest1 sudo ip netns add nstest1 sudo ip netns exec nstest1 ip link set dev lo up sudo ip link add veth-a type veth peer name veth-1 sudo ip link set veth-1 netns nstest1 sudo ip netns exec nstest1 ip addr add 10.0.1.1/24 dev veth-1 sudo ip netns exec nstest1 ip link set dev veth-1 up # setup namespace nstest2 sudo ip netns add nstest2 sudo ip netns exec nstest2 ip link set dev lo up sudo ip link add veth-b type veth peer name veth-2 sudo ip link set veth-2 netns nstest2 sudo ip netns exec nstest2 ip addr add 10.0.2.1/24 dev veth-2 sudo ip netns exec nstest2 ip link set dev veth-2 up # setup default namespace sudo ip addr add 10.0.1.2/24 dev veth-a sudo ip link set dev veth-a up sudo ip addr add 10.0.2.2/24 dev veth-b sudo ip link set dev veth-b up
When I ping nstest1 from the default namespace or vice-versa all pings are successful. When I try to ping nstest2 from the default namespace or vice-versa all pings fail. I cannot understand why that happens and how it can be fixed. Should I manually add the routes from/to default namespace to nstest2? If yes why I don't have to do it for nstest1? Any help with explanation will be greatly appreciated! I'm using ubuntu 12.10.
EDIT:
The route tables are the following for each namespace:
Default namespaceKernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 10.0.2.2 0.0.0.0 UG 0 0 0 eth0 10.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 veth-a 10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 veth-b 192.168.56.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
nstest1Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.0.1.0 0.0.0.0 255.255.255.0 U 0 0 0 veth-1
nstest2Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 10.0.2.0 0.0.0.0 255.255.255.0 U 0 0 0 veth-2
EDIT 2
It turns out that 10.0.2.2 is assigned to eth0 therefore there is a collision by assigning the same subnet to veth-b and veth-2. When I changed it to 10.0.3.1/24 and 10.0.3.2/24 ping worked for both nstest1 and nstest2. Doing anifconfig -a
is necessary before assigning those addresses. -
etherfish over 10 yearsOh, the reason why pinging nstest2 wouldn't work is because you had two routes for the same subnet, 10.0.0.0/24 on two different devices, veth-a and veth-b. Since veth-a was the first match in the routing table for any IP address in 10.0.0.0/24 (meaning any ip from 10.0.0.0 to 10.0.0.255), it tried to reach it via veth-a and not veth-b. That's why you need two different subnets.
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Vasilis over 10 yearsThanks! +1 for correcting my sub-netting error, but I still cannot ping. I edited the question with different subnets for each pair of virtual interfaces and I added the routing tables for each namespace. The problem may be with my default gateway but I'm not sure.