Hi,

Can someone tell how the ip command is able to fetch the ipv6 gateway details.

[root@CuCM-210 ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
DEVICE=eth0
TYPE=Ethernet
UUID=9e01d4c0-04b7-4d1c-aa31-3bf13f6b9576
ONBOOT=yes
NM_CONTROLLED=yes
BOOTPROTO=none
IPADDR=10.126.155.210
NETMASK=255.255.255.0
GATEWAY=10.126.155.1
IPV6INIT=yes
IPV6ADDR=2001:155:155:155:250:56ff:fe8c:5a92/64
IPV6_AUTOCONF=no
DHCPV6C=no

IPV6_AUTOCONF & DHCPV6C is set to no, and gateway is not statically set, but still ip -6 route command is able to fetch the ipv6 gateway details, not sure from where.

[root@linux ~]# ip -6 route | grep ^default
default via fe80::224:98ff:fe15:8800 dev eth0 proto kernel metric 1024 expires 1779sec mtu 1500 advmss 1440 hoplimit 64

Can some one explain this.

Thanks,
Joe

IPv6 works very differently from IPv4 when it comes to gateways.

With IPv4, you need to specify a gateway manually or via a DHCP option. With IPv6, the IP stack locates gateways automatically by using ICMP-v6 Neighbor Discovery packets. Specifically, a client will listen for Router Advertisements, which may be sent gratuitously by a router or as a response to a Router Solicitation package.

This mechanism works independently of IPv6 Stateless Address Autoconfiguration (SLAAC) and DHCPv6. It is possible to turn it off with /proc/sys/net/ipv6/conf/<interface>/accept_ra_defrtr and/or /proc/sys/net/ipv6/conf/<interface>/accept_ra. The kernel documentation will tell you which values are valid for those two settings, and what they do.

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