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I am currently setting up IPv6 on my network ran by a SRX-240H2 as router. Besides others the router as an internal interface configured as follows:

[edit interfaces ge-0/0/4 unit 802]
clb@srx01-av# show 
description "Management V-LAN";
vlan-id 802;
family inet {
    address 192.168.224.254/22;
}
family inet6 {
    address 2a00:12c0:101b:01f0::0254/64 {
        primary;
        preferred;
    }
}

Besides the 2a00 global address the interface also configures a link local address.

clb@srx01-av> show interfaces ge-0/0/4.802 terse 
Interface               Admin Link Proto    Local                 Remote
ge-0/0/4.802            up    up   inet     192.168.224.254/22
                                   inet6    2a00:12c0:101b:1f0::254/64
                                            fe80::5e45:2703:2209:e784/64

I configured the RAs to include the Prefix:

[edit protocols router-advertisement interface ge-0/0/4.802]
clb@srx01-av# show 
max-advertisement-interval 60;
min-advertisement-interval 20;
no-managed-configuration;
other-stateful-configuration;
prefix 2a00:12c0:101b:1f0::/64;

Unfortunately the router does send out RAs with the Link local source address and not the global address. This can be seen in a tcpdump from one of the hosts on the network:

host ~ # tcpdump -n -i eth0 icmp6
22:30:33.433466 IP6 fe80::5e45:2703:2209:e784 > ff02::1: ICMP6, router advertisement, length 56

Can I somehow configure the router to send the RAs with the "correct" address or am I getting a basic concept of IPv6 RA wrong?

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2 Answers 2

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6

As per the RFC, link-local addresses will be used for any Neighbour Discovery including RA messages.
Source: https://www.rfc-editor.org/rfc/rfc4861#section-4.2

PacketLife has a good blog post that clearly explains Neighbour Discovery.
http://packetlife.net/blog/2008/aug/28/ipv6-neighbor-discovery/

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  • Thanks for the clarification. Does that mean that the clients will always use a link-local address as default route when discovered via RA? In my case routing does not work when using the link-local address as default gateway. Only the other (2a00) address works.
    – Clemens Bergmann
    Commented Mar 16, 2018 at 13:00
  • @ClemensBergmann A lot of clients assign an interface scope to the default route (so the route is only used for traffic that originated from that interface) on IPv6 if they do not have a default ipv4 route, this could be what is happening if you don't have ipv4 configured. I've run into that issue on Mac and Ubuntu machines. Check if this works: ping <ipv6-address>%en0 (replace en0 with your interface name) Then you can check routing with route or netstat -nr, and see if the default route has an "I" under Flags. That would mean it has an interface scope.
    – dogoncouch
    Commented Mar 26, 2019 at 22:15
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in JUNOS you can set the prefix which is advertised:

set protocols router-advertisement interface <> prefix ....

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