centos flannel vxlan, ping cross host failed

[CocaCola183]

I have tried udp as backend and there is no problem, but when I use vxlan, I can not ping cross host.

what I have read:

• How to determine why flannelized IPs can't see one another?  #216
• How to debug flannel issues across nodes? #370
• Connect issues with flannel on Centos 6.6 #111
• Flannel ping ICMP packets not routed back properly #415
• Flannel stops working on EC2 #87
• Routing errors in Kubernetes Cluster #481

linux info: CentOS release 6.8 (Final)

kernnel version: 2.6.32-573.22.1.el6.x86_64

docker version: 1.7.1

vxlan support:

$ sudo modprobe vxlan && echo $?
0

$ ip link add type vxlan help
Usage: ... vxlan id VNI [ group ADDR ] [ local ADDR ]
                 [ ttl TTL ] [ tos TOS ] [ dev PHYS_DEV ]
                 [ port MIN MAX ] [ [no]learning ]
                 [ [no]proxy ] [ [no]rsc ]
                 [ [no]l2miss ] [ [no]l3miss ]

Where: VNI := 0-16777215
       ADDR := { IP_ADDRESS | any }
       TOS  := { NUMBER | inherit }
       TTL  := { 1..255 | inherit }

sames support vxlan

etcd version:

$ etcd --version
etcd Version: 3.0.16
Git SHA: a23109a
Go Version: go1.6.4
Go OS/Arch: linux/amd64

flanneld version: v0.7.0

route:
172.17.0.0 * 255.255.0.0 U 0 0 0 flannel.1

flannel config:

{ "Network": "172.17.0.0/16", "SubnetLen": 24, "Backend": { "Type": "vxlan", "VNI": 1, "Port": 8472 }}

port:

subnet info:
/coreos.com/network/subnets/172.17.49.0-24
/coreos.com/network/subnets/172.17.70.0-24
/coreos.com/network/subnets/172.17.63.0-24

flannel log:

It sames that adding subnet not done, but there is no error info and ping failed cross host. What's the right output when add subnet succeeds?

ping:

arp -v 
172.17.49.0                      (incomplete)                              flannel.1

What should I do? Is there any way to fix or debug this problem? Thank you!

[tomdee]

Your kernel version is very old and I assume has limited vxlan support. Flannel really should provide some indication that it's not working, but doesn't appear to at the moment.

From a quick internet search, it would seem that a Kernel version of >3.9 is normally recommended, though this page does seem to say that Centos >6.5 should be enough for VXLAN in general -http://docs.cloudstack.apache.org/en/latest/networking/vxlan.html

[CocaCola183]

@tomdee Thanks for response.

I thought my system support vxlan after read this: http://docs.cloudstack.apache.org/en/latest/networking/vxlan.html#check-the-capability-of-your-system

I think flannel should give some more advise about Kernel version, there is no specific error info when I use, after all.