Re: [lwip-devel] IPv6 L2TP PPP review

[Sylvain Rochet]

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

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