IPv6 - eth0 on loopback

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Lloydz
Posts: 4
Joined: 2018/07/22 14:50:11

IPv6 - eth0 on loopback

Post by Lloydz » 2018/07/22 16:46:33

Hi,

i have some trouble with ipv4 and ipv6 dual stack on my centos box. I think it isn't right, that my IPv6 addresses from eth0 was routed via loopback in the IPv6 routing-table. But/And i don't know why. Here are the facts:

First, the CentOS version i use:
root@computer:/home/john# cat /etc/centos-release
CentOS Linux release 7.5.1804 (Core)


The following three scripts are the CentOS Network Configuration Scripts in generally
used by the system with and without NetworkManager. I don't use NetworkManager:

The meta network config-script:
root@computer:/home/john# cat /etc/sysconfig/network
NETWORKING=yes
NETWORKING_IPV6=yes
GATEWAYDEV=eth0
GATEWAY=xxx.xxx.xxx.1
IPV6_DEFAULTGW=xxxx:xxxx::1
IPV6_AUTOTUNNEL=no
NOZEROCONF=true


I have two IPv4 addresses, that is the reason why there are ifcfg-eth0 and ifcfg-eth0:1.
ifcfg-eth0 has also the two IPv6 addresses. if-cfg-eth0:1 has only the second IPv4 address:
root@computer:/home/john# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
BOOTPROTO=none
ONBOOT=yes
NM_CONTROLLED=no
USERCTL=no
TYPE=Ethernet
IPADDR=xxx.xxx.xxx.2
NETMASK=255.255.255.0
GATEWAY=xxx.xxx.xxx.1
DEFROUTE=yes
IPV6INIT=yes
IPV6_AUTOCONF=no
IPV6_DEFROUTE=yes
IPV6_FAILURE_FATAL=no
IPV6ADDR=xxxx:xxxx::2/64
IPV6ADDR_SECONDARIES=xxxx:xxxx::3/64
IPV6_DEFAULTGW=xxxx:xxxx::1
IPV6_DEFAULTDEV=eth0
PEERDNS=no
PEERROUTES=no
IPV6_PEERDNS=no
IPV6_PEERROUTES=no
DNS1=127.0.0.1
DNS2=::1

root@computer:/home/john# cat /etc/sysconfig/network-scripts/ifcfg-eth0:1
DEVICE=eth0
BOOTPROTO=none
ONBOOT=yes
IPADDR=xxx.xxx.xxx.3
NETMASK=255.255.255.0


After the System has started, the following IP settings are made:
root@computer:/home/john# ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 00:00:00:00:00:00 brd ff:ff:ff:ff:ff:ff
inet xxx.xxx.xxx.2/24 brd xxx.xxx.xxx.255 scope global eth0 <- The first IPv4 Address
valid_lft forever preferred_lft forever
inet xxx.xxx.xxx.3/24 brd xxx.xxx.xxx.255 scope global eth0 <- The second IPv4 Address
valid_lft forever preferred_lft forever
inet6 xxxx:xxxx::2/64 scope global <- The first IPv6 Address
valid_lft forever preferred_lft forever
inet6 xxxx:xxxx::3/64 scope global <- The second IPv6 Address
valid_lft forever preferred_lft forever
inet6 fe80::xxxx:xxxx:xxxx:xxxx/64 scope link
valid_lft forever preferred_lft forever


.. and the routing-table (first IPv4 and then IPv6):
root@computer:/home/john# route -4n
Kernel IP Routentabelle
Ziel Router Genmask Flags Metric Ref Use Iface
0.0.0.0 xxx.xxx.xxx.1 0.0.0.0 UG 0 0 0 eth0
xxx.xxx.xxx.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 <- First IPv4 Network
xxx.xxx.xxx.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 <- Second IPv4 Network

everything ist fine and is working on IPv4 layer.

Now comes the IPv6 routing-table:
root@computer:/home/john# route -6n
Kernel IPv6 Routentabelle
Destination Next Hop Flag Met Ref Use If
::/96 :: !n 1024 0 0 lo
0.0.0.0/96 :: !n 1024 0 0 lo
2002:a00::/24 :: !n 1024 0 0 lo
2002:7f00::/24 :: !n 1024 0 0 lo
2002:a9fe::/32 :: !n 1024 0 0 lo
2002:ac10::/28 :: !n 1024 0 0 lo
2002:c0a8::/32 :: !n 1024 0 0 lo
2002:e000::/19 :: !n 1024 0 0 lo
2a0a:51c0::/64 :: U 256 1 7 eth0
3ffe:ffff::/32 :: !n 1024 0 0 lo
fe80::/64 :: U 256 0 0 eth0
::/0 xxxx:xxxx::1 UG 1 1 217 eth0
::/0 :: !n -1 1 351 lo
::1/128 :: Un 0 2 63 lo
xxxx:xxxx::2/128 :: Un 0 2 2 lo
xxxx:xxxx::3/128 :: Un 0 2 660 lo
fe80::xxxx:xxxx:xxxx:xxxx/128 :: Un 0 1 0 lo
ff00::/8 :: U 256 1 7079 eth0
::/0 :: !n -1 1 351 lo

That it is, what i'm not understand. In the routing table both IPv6 addresses stands on
loopback device and not on my eth0 ethernet-card.
I think similar in the IPv4 routing table, the IP must have an relation between the device (eth0) and the
address. And has eth0 and not lo.

The result is: i can't ping IPv6 Adresses. In example ipv6.google.com:
root@computer:/home/john# ping6 -c4 ipv6.google.com
PING ipv6.google.com(fra15s18-in-x0e.1e100.net (2a00:1450:4001:81d::200e)) 56 data bytes
From computer (xxxx.xxxx::2) icmp_seq=1 Destination unreachable: Address unreachable
From computer (xxxx.xxxx::2) icmp_seq=2 Destination unreachable: Address unreachable
From computer (xxxx.xxxx::2) icmp_seq=3 Destination unreachable: Address unreachable
From computer (xxxx.xxxx::2) icmp_seq=4 Destination unreachable: Address unreachable

--- ipv6.google.com ping statistics ---
4 packets transmitted, 0 received, +4 errors, 100% packet loss, time 3001ms


.. my IPv6 Gateway:
root@computer:/home/john# ping6 -c4 xxxx:xxxx::1
PING xxxx:xxxx::1(xxxx:xxxx::1) 56 data bytes
From xxxx:xxxx::2 icmp_seq=1 Destination unreachable: Address unreachable
From xxxx:xxxx::2 icmp_seq=2 Destination unreachable: Address unreachable
From xxxx:xxxx::2 icmp_seq=3 Destination unreachable: Address unreachable
From xxxx:xxxx::2 icmp_seq=4 Destination unreachable: Address unreachable

--- xxxx:xxxx::1 ping statistics ---
4 packets transmitted, 0 received, +4 errors, 100% packet loss, time 3000ms


At last, the localhost on loopback. So i think in principle IPv6 is working on the
maschine:
root@computer:/home/john# ping6 -c4 ::1
PING ::1(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.058 ms
64 bytes from ::1: icmp_seq=2 ttl=64 time=0.064 ms
64 bytes from ::1: icmp_seq=3 ttl=64 time=0.066 ms
64 bytes from ::1: icmp_seq=4 ttl=64 time=0.077 ms

--- ::1 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 2999ms
rtt min/avg/max/mdev = 0.058/0.066/0.077/0.009 ms


With IPv4 now everything is working, but not with IPv6. I don't want to use NetworkManager, so i deactivate it before. There are 4 IP addresses, 2 IPv4 and 2 IPv6 in dual stack on one network interface card. I don't understand why IPv6 don't work.

thanks for your attention.
Last edited by Lloydz on 2018/07/23 14:51:47, edited 1 time in total.

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TrevorH
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Posts: 23204
Joined: 2009/09/24 10:40:56
Location: Brighton, UK

Re: IPv6 - eth0 on loopback

Post by TrevorH » 2018/07/22 19:20:41

You have obscured so much information in your post that it is almost impossible for anyone to help you. You need to leave enough clues there so we know what is what and where.
CentOS 5 died in March 2017 - migrate NOW!
Full time Geek, part time moderator. Use the FAQ Luke

Lloydz
Posts: 4
Joined: 2018/07/22 14:50:11

Re: IPv6 - eth0 on loopback

Post by Lloydz » 2018/07/23 14:59:23

Hopefully now it is a little bit more clear.

Lloydz
Posts: 4
Joined: 2018/07/22 14:50:11

Re: IPv6 - eth0 on loopback

Post by Lloydz » 2018/07/25 15:18:04

Ok. Can someone confirm, that my configuration files "/etc/sysconfig/network", "/etc/sysconfig/network-scripts/ifcfg-eth0" and "/etc/sysconfig/network-scripts/ifcfg-eth0:1" are ok? I'm not using NetworkManager(!).


thanks!

Lloydz
Posts: 4
Joined: 2018/07/22 14:50:11

Re: IPv6 - eth0 on loopback

Post by Lloydz » 2018/08/07 16:01:24

Now I'm happy. My configuration are ok. The Problem was missing rules for ipv6-icmp in ip6tables.

Thanks a lot.
bye.

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