[194152] in North American Network Operators' Group
IPv6 oddness in Comcast land...
daemon@ATHENA.MIT.EDU (valdis.kletnieks@vt.edu)
Sun Mar 19 19:17:32 2017
X-Original-To: nanog@nanog.org
From: valdis.kletnieks@vt.edu
To: nanog@nanog.org
Date: Sun, 19 Mar 2017 19:16:11 -0400
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
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Trying to figure out what the heck is going on here. Any good
explanations cheerfully accepted.
Background: Home internet router is a Linksys WRT1200AC that had been
running OpenWRT 15.05.01. IPv6 worked just fine - Comcast handed me a /60
via DHCP-PD and no issues. I reflashed it to Lede 17.01, and after doing
all the reconfig, I'm hitting a really strange IPv6 issue.
Symptoms - IPv6 still configures correctly, but IPv6 packets appear to go out
and disappear into the ether when they leave the Linksys. Doing a traceroute
to any IPv6 destination makes things work again - for a while (from 15 minutes
to an hour or two).
As seen from my laptop (I have the matching tcpdump from the outbound
interface on the Linksys):
[~] ping -6 -c 3 listserv.vt.edu
PING listserv.vt.edu(listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769)) 56 data bytes
--- listserv.vt.edu ping statistics ---
3 packets transmitted, 0 received, 100% packet loss, time 2070ms
[~] traceroute -6 listserv.vt.edu
traceroute to listserv.vt.edu (2001:468:c80:2105:211:43ff:feda:d769), 30 hops max, 80 byte packets
1 2601:5c0:c001:69e2::1 (2601:5c0:c001:69e2::1) 2.417 ms 3.077 ms 5.358 ms
2 * * *
3 * * *
4 * * *
5 * * *
6 * hu-0-10-0-7-pe04.ashburn.va.ibone.comcast.net (2001:558:0:f5c1::2) 31.478 ms 31.975 ms
7 2001:559::d16 (2001:559::d16) 32.406 ms 17.102 ms 24.751 ms
8 2001:550:2:2f::a (2001:550:2:2f::a) 23.245 ms 23.519 ms 22.185 ms
9 2607:b400:f0:2003::f0 (2607:b400:f0:2003::f0) 29.782 ms 28.604 ms 29.891 ms
10 2607:b400:90:ff05::f1 (2607:b400:90:ff05::f1) 30.423 ms * 30.680 ms
11 * * *
12 listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769) 34.562 ms 39.072 ms 24.633 ms
[~] ping -6 -c 3 listserv.vt.edu
PING listserv.vt.edu(listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769)) 56 data bytes
64 bytes from listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769): icmp_seq=1 ttl=53 time=33.3 ms
64 bytes from listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769): icmp_seq=2 ttl=53 time=24.3 ms
64 bytes from listserv.ipv6.vt.edu (2001:468:c80:2105:211:43ff:feda:d769): icmp_seq=3 ttl=53 time=46.0 ms
--- listserv.vt.edu ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 24.334/34.595/46.093/8.927 ms
So it looks like something times out somewhere and fails to pass packets
back.
TCP connections don't keep IPv6 alive. I have a browser window that
auto-updates every 5 minutes, and a SmokePing process on a Raspberri Pi uploads
to a server at work every few minutes, and those eventually drop back to IPv4
when the IPv6 TCP fails to connect. And normal UDP doesn't seem to keep it
alive - NTP pointing at IPv6 peers loses connectivity as well.
But a traceroute wakes it up. It's almost like some router is losing the
route to me out of the FIB, and fixes it when it has to handle a packet
on the CPU slow path (like send back a 'time exceeded'). But I'm mystified
why this started when I reflashed my router.
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