Re: [lwip-devel] IPv6 L2TP PPP review

[Ivan Delamer]

Hi Sylvain,

Ok, now I understand the scenario a bit better.

For neighbour discovery to work, you need to be subscribed to the 
solicited-node multicast address.

This is usually done automatically when you set the state to TENTATIVE.

If you set the address manually to PREFERRED, then you must join the 
multicast group manually:

ip6_addr_set_solicitednode(&multicast_address, netif_ip6_addr(netif, 
1)->addr[3]);
mld6_joingroup(netif_ip6_addr(netif, 1), &multicast_address);

This will allow ND multicast packets into the stack.

If you have a PPP link, I suspect ND is not used and you just send the 
packets to the neighbour, so in that case you wouldn't need this.

I believe your address is up and running correctly, it just isn't 
discoverable. But in PPP you don't do discovery.

Cheers
Ivan



> Date: Tue, 3 Mar 2015 22:01:33 +0100
> From: Sylvain Rochet <address@hidden>
> To: lwip-devel <address@hidden>
> Subject: Re: [lwip-devel] IPv6 L2TP PPP review
> Message-ID: <address@hidden>
> Content-Type: text/plain; charset="utf-8"
>
> Hello Ivan,
>
>
> On Tue, Mar 03, 2015 at 10:25:30AM -0700, Ivan Delamer wrote:
> > The initial state you should set for your address depends on whether
> > you have DAD enabled or not.
> >
> > If DAD is enabled (usual case), you should set it to
> > IP6_ADDR_TENTATIVE.
>
> Doing that work.
>
>
> > If DAD is disabled, you should set it to IP6_ADDR_PREFERRED.
>
> Doing that doesn't seem to work.
>
>
> > I think that in a PPP link DAD is actually not required, and
> > probably wouldn't work because it requires multicast support. So I
> > would set the state to IP6_ADDR_PREFERRED and it should work.
>
> I forgot to tell, but this was on plain Ethernet.
>
> I am using the following in ppp.c and it works fine:
>
>   ip6_addr_copy(pcb->netif->ip6_addr[0], pcb->addrs.our6_ipaddr);
>   netif_ip6_addr_set_state(pcb->netif, 0, IP6_ADDR_PREFERRED);
>
> IP6CP only negotiate a link local address, user is then responsible to
> configure use static addressing (or use DHCPv6).
>
>
>
> > I'm not sure why IP6_ADDR_VALID wouldn't work, although generally
> > you want it to be either PREFERRED or DEPRECATED, which is VALID
> > with an extra flag.
> >
> > What are you seeing that makes you say "it didn't work"?
>
> On Linux host:
>
> # ip -6 address add 2001::1/64 dev tap0
>
>
> Inside lwIP:
>
> Netif is just the interface on the other side of tap0, nothing 
> complicated.
>
> Dup detect enabled, using IP6_ADDR_TENTATIVE:
>
>   netif.ip6_addr[1].addr[0] = PP_HTONL(0x20010000);
>   netif.ip6_addr[1].addr[1] = PP_HTONL(0x00000000);
>   netif.ip6_addr[1].addr[2] = PP_HTONL(0x00000000);
>   netif.ip6_addr[1].addr[3] = PP_HTONL(0x00000002);  /* 2001::2 */
>   netif_ip6_addr_set_state(&netif, 1, IP6_ADDR_TENTATIVE);
>   netif_create_ip6_linklocal_address(&netif, 1);
>
> It works:
>
> # ping6 -I tap0 fe80::0012:34ff:fe56:7800
> PING fe80::0012:34ff:fe56:7800(fe80::12:34ff:fe56:7800) from
> fe80::a034:6ff:fed1:d95c tap0: 56 data bytes
> 64 bytes from fe80::12:34ff:fe56:7800: icmp_seq=1 ttl=255 time=0.120 
> ms
>
> $ ping6 2001::2
> PING 2001::2(2001::2) 56 data bytes
> 64 bytes from 2001::2: icmp_seq=1 ttl=255 time=0.134 ms
>
>
>
> Dup detect disabled (or enabled, it doesn't change the result),
> IP6_ADDR_TENTATIVE disabled, interface forced VALID,PREFERRED:
>
>   netif.ip6_addr[1].addr[0] = PP_HTONL(0x20010000);
>   netif.ip6_addr[1].addr[1] = PP_HTONL(0x00000000);
>   netif.ip6_addr[1].addr[2] = PP_HTONL(0x00000000);
>   netif.ip6_addr[1].addr[3] = PP_HTONL(0x00000002);
>   netif_ip6_addr_set_state(&netif, 1, IP6_ADDR_PREFERRED);
>   netif_create_ip6_linklocal_address(&netif, 1);
>
> Link local is still working:
>
> # ping6 -I tap0 fe80::0012:34ff:fe56:7800
> PING fe80::0012:34ff:fe56:7800(fe80::12:34ff:fe56:7800) from
> fe80::484:3bff:febd:d33f tap0: 56 data bytes
> 64 bytes from fe80::12:34ff:fe56:7800: icmp_seq=1 ttl=255 time=0.123 
> ms
>
> Link global doesn't work:
>
> $ ping6 2001::2
> PING 2001::2(2001::2) 56 data bytes
> From 2001::1 icmp_seq=1 Destination unreachable: Address unreachable
>
> I am sending neighbor solicitation requests but I don't get any 
> answer:
>
> # tcpdump -vvvv -i tap0 -n -p
> tcpdump: listening on tap0, link-type EN10MB (Ethernet), capture size
> 262144 bytes
> 21:58:07.782247 IP6 (hlim 255, next-header ICMPv6 (58) payload
> length: 32) 2001::1 > ff02::1:ff00:2: [icmp6 sum ok] ICMP6, neighbor
> solicitation, length 32, who has 2001::2
>           source link-address option (1), length 8 (1): 06:84:3b:bd:d3:3f
>             0x0000:  0684 3bbd d33f
> 21:58:08.782208 IP6 (hlim 255, next-header ICMPv6 (58) payload
> length: 32) fe80::484:3bff:febd:d33f > ff02::1:ff00:2: [icmp6 sum ok]
> ICMP6, neighbor solicitation, length 32, who has 2001::2
>           source link-address option (1), length 8 (1): 06:84:3b:bd:d3:3f
>             0x0000:  0684 3bbd d33f
> 21:58:09.782193 IP6 (hlim 255, next-header ICMPv6 (58) payload
> length: 32) 2001::1 > ff02::1:ff00:2: [icmp6 sum ok] ICMP6, neighbor
> solicitation, length 32, who has 2001::2
>           source link-address option (1), length 8 (1): 06:84:3b:bd:d3:3f
>             0x0000:  0684 3bbd d33f
>
>
> Cheers,
> Sylvain