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From: Thomas Habets on 13 Aug 2010 14:30

(originally sent to netdev on aug 6th)

IPv6 initially works, but when I leave it alone overnight I'm unable to ping
even my default gw.

Static global IPv6 addresses configured on both ends. No access lists on either
end.

Kernel version: 2.6.35 mainline (amd64) and 2.6.33.6.
Kernel config: http://pastebin.com/raw.php?i=Y6S8iKW7
Dist: Debian Lenny (5.0.5), nothing special to my knowledge.

I seem to have the same issue that Mikael Abrahamsson encountered with Ubuntu
kernels 2.6.26.3, 2.6.26-5-generic and 2.6.27-2-generic, and mainline kernels
2.6.25, 2.6.26 and 2.6.27:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/263260

He got IPv6 running again without rebooting using "networking stop, ifconfig
eth0 down, networking start, kill dhclient", while I narrowed it down to just
deleting the ipv6 neighbor (ip ne del..., see below). Rebooting also causes it
to start working again.

It's very reproducible. I just leave it overnight and it breaks every time.

I am willing and able to try patches at any time, the box is not in production.

No iptables, no ip6tables. IP6tables support is not even compiled in.

NIC is "Broadcom Corporation NetXtreme BCM5715 Gigabit ethernet (rev a3)"
according to lspci.

Other end is a directly connected Cisco 7600 (routed port) that I have access
to, but it's in production use. IPv4 works perfectly over this same port. Only
lo and eth0 are UP.


Output when broken
------------------
$ uname -a
Linux XXXXX 2.6.35 #1 SMP Tue Aug 3 09:25:51 CEST 2010 x86_64
GNU/Linux

$ ip -6 a sh
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 16436
inet6 2a00:800:1000:64::1/128 scope global
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 qlen 1000
inet6 2a00:800:752:1::5c:2/112 scope global
valid_lft forever preferred_lft forever
inet6 fe80::224:81ff:fea3:4424/64 scope link
valid_lft forever preferred_lft forever

(I have tried removing 2a00:800:1000:64::1/128 from lo, same issue)

$ ip -6 r sh
2a00:800:752:1::5c:0/112 dev eth0 proto kernel metric 256 mtu 1500
advmss 14 hoplimit 4294967295 unreachable
2a00:800:1000:64::1 dev lo proto kernel metric 256 error -101 mtu 16436
advmss 16376 hoplimit 4294967295
fe80::/64 dev eth0 proto kernel metric 256 mtu 1500 advmss 1440
hoplimit 4294967295
default via 2a00:800:752:1::5c:1 dev eth0 metric 1024 mtu 1500 advmss 1440
hoplimit 4294967295

$ ping6 2a00:800:752:1::5c:1
PING 2a00:800:752:1::5c:1(2a00:800:752:1::5c:1) 56 data bytes
^C
--- 2a00:800:752:1::5c:1 ping statistics ---
22 packets transmitted, 0 received, 100% packet loss, time 21006ms


# Tcpdpump on the problem machine shows mostly the pings, but also periodically
some ND:

[...]
12:54:02.683672 00:24:81:a3:44:24 > 00:22:55:17:4b:80, ethertype IPv6
(0x86dd), length 118: 2a00:800:752:1::5c:2 > 2a00:800:752:1::5c:1: ICMP6, echo
request, seq 12, length 64
12:54:02.693669 00:24:81:a3:44:24 > 00:22:55:17:4b:80, ethertype IPv6
(0x86dd), length 86: fe80::224:81ff:fea3:4424 > 2a00:800:752:1::5c:1: ICMP6,
neighbor solicitation, who has 2a00:800:752:1::5c:1, length 32
12:54:02.693832 00:22:55:17:4b:80 > 00:24:81:a3:44:24, ethertype IPv6
(0x86dd), length 78: 2a00:800:752:1::5c:1 > fe80::224:81ff:fea3:4424: ICMP6,
neighbor advertisement, tgt is 2a00:800:752:1::5c:1, length 24
12:54:03.683672 00:24:81:a3:44:24 > 00:22:55:17:4b:80, ethertype IPv6
(0x86dd), length 118: 2a00:800:752:1::5c:2 > 2a00:800:752:1::5c:1: ICMP6, echo
request, seq 13, length 64
[...]

$ ip -6 ne
fe80::222:55ff:fe17:4b80 dev eth0 lladdr 00:22:55:17:4b:80 router STALE
2a00:800:752:1::5c:1 dev eth0 lladdr 00:22:55:17:4b:80 router STALE


Fixing the adjacency
--------------------
$ ping6 2a00:800:752:1::5c:1
PING 2a00:800:752:1::5c:1(2a00:800:752:1::5c:1) 56 data bytes
^C
--- 2a00:800:752:1::5c:1 ping statistics ---
51 packets transmitted, 0 received, 100% packet loss, time 50006ms

$ sudo ip ne del 2a00:800:752:1::5c:1 dev eth0
$ ping6 2a00:800:752:1::5c:1
PING 2a00:800:752:1::5c:1(2a00:800:752:1::5c:1) 56 data bytes
64 bytes from 2a00:800:752:1::5c:1: icmp_seq=1 ttl=64 time=31.9 ms
64 bytes from 2a00:800:752:1::5c:1: icmp_seq=2 ttl=64 time=0.212 ms

$ ip -6 ne
fe80::222:55ff:fe17:4b80 dev eth0 lladdr 00:22:55:17:4b:80 router REACHABLE
2a00:800:752:1::5c:1 dev eth0 lladdr 00:22:55:17:4b:80 router REACHABLE

(Note that after a few minutes it goes back to STALE, but pinging still works
and brings back the state to REACHABLE, so it's not that it can't get out of
STALE once there, it seems).

---------
typedef struct me_s {
char name[] = { "Thomas Habets" };
char email[] = { "thomas(a)habets.pp.se" };
char kernel[] = { "Linux" };
char *pgpKey[] = { "http://www.habets.pp.se/pubkey.txt" };
char pgp[] = { "A8A3 D1DD 4AE0 8467 7FDE 0945 286A E90A AD48 E854" };
char coolcmd[] = { "echo '. ./_&. ./_'>_;. ./_" };
} me_t;
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Prev: Proposal: Use hi-res clock for file timestamps
Next: [PATCH 1/1] kfifo: fix DMA sample driver