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I have a /64 IP subnet and I divided this subnet into /96 subnets in order to use it in the internal and external interfaces of my CentOS machine. The problem is that I can ping an address like ipv6.google.com on the internet from the external interface of the CentOS box, also I can ping the clients connected to the internal interface, I also can ping the external interface from another ipv6 configured client in another location. But I cannot ping ipv6.google.com from the clients. It seems like clients' traffic is not routed from the internal to the external interface. Is there a problem with the configuration or the subnetting? The corresponding configuration is as follows;

IP subnet: 2a01:358:4000:1f::/64

External Interface Configuration:

BOOTPROTO=static

DEVICE=eth3

IPADDR=88.255.50.50

NETMASK=255.255.255.248

ONBOOT=yes
NOZEROCONF=yes

IPV6INIT=yes

IPV6ADDR="2A01:358:4000:1F::2/96"

IPV6_DEFAULTGW=2A01:358:4000:1F::1

Internal Interface Configuration:

BOOTPROTO=static

DEVICE=eth0

IPADDR=10.0.0.254

NETMASK=255.255.255.0

ONBOOT=yes

NOZEROCONF=yes

IPV6INIT=yes

IPV6ADDR="2A01:358:4000:1F:0:1:0:1/96"

**/etc/sysconfig/network Configuration:**

NETWORKING=yes

NETWORKING_IPV6=yes

HOSTNAME=hostname

ipv6 forwarding configuration:

net.ipv6.conf.eth3.forwarding = 1

net.ipv6.conf.eth0.forwarding = 1

net.ipv6.conf.default.forwarding = 1

net.ipv6.conf.all.forwarding = 1

net.ipv6.conf.lo.forwarding = 1

ipv6 Routing Table:

Kernel IPv6 routing table


Destination  Next Hop  Flags  Metric  Ref  Use Iface

2a01:358:4000:1f::/96                       ::                                      U     256    2        0 eth3    
2a01:358:4000:1f:0:1::/96                   ::                                      U     256    0        0 eth0    
2000::/3                                    2a01:358:4000:1f::1                     UG    1      1249       0 eth3    
fe80::/64                                   ::                                      U     256    0        0 eth0    
fe80::/64                                   ::                                      U     256    0        0 eth3    
::/0                                        2a01:358:4000:1f::1                     UG    1      0        0 eth3    
::1/128                                     ::                                      U     0      3048       2 lo      
2a01:358:4000:1f::/128                      ::                                      U     0      0        2 lo      
2a01:358:4000:1f::2/128                     ::                                      U     0      4        1 lo      
2a01:358:4000:1f:0:1::/128                  ::                                      U     0      0        2 lo      
2a01:358:4000:1f:0:1:0:1/128                ::                                      U     0      253       1 lo      
fe80::/128                                  ::                                      U     0      0        2 lo      
fe80::/128                                  ::                                      U     0      0        2 lo      
fe80::21b:21ff:fec9:648f/128                ::                                      U     0      405       1 lo      
fe80::3a60:77ff:fe26:be7/128                ::                                      U     0      420       1 lo      
ff00::/8                                    ::                                      U     256    0        0 eth0    
ff00::/8                                    ::                                      U     256    0        0 eth3    
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You understand that somethings start to break if you have a subnet prefix that isn't `/64? –  Zoredache Jan 3 '13 at 20:15
    
Have you checked your ip6tables rules to ensure it's not the firewall blocking the traffic? –  fukawi2 Jan 3 '13 at 22:38
    
Yes I checked it. ip6tables is set to allow everything. –  Yakup Kaya Jan 4 '13 at 11:23

1 Answer 1

What subnetmask and route table does 2A01:358:4000:1F::1 have? If you haven't changed the mask to /96, and added a route for your internal network, on that router, then what you have done, simply won't work.

Short of doing something hacky, you can't simply change the subnet mask on one device without changing it on all the devices on the 2A01:358:4000:1F/64 network, which includes the device acting as the default gateway.

Ideally you should get an additional subnet, and have another /64 anyway.

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1  
Your ISP should give you plenty of /64 subnets. Usually a /56 or a /48 that you can use to create 256 or 65536 /64 subnets out of. If they don't then complain: they should –  Sander Steffann Jan 3 '13 at 20:32

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