Hello,
Using OpenBSD 6.2, I'm trying to setup a CARP interface with IPV6 address. My
gateway require a 1480 MTU (1420 mss), but I can't figure out how to tell the
system to use that value for the CARP iface.
I have setup my main interface with a 1480 mtu and ipv6 eui64:
ifconfig vio0
vio0:
flags=8b43<UP,BROADCAST,RUNNING,PROMISC,ALLMULTI,SIMPLEX,MULTICAST> mtu 1480)
lladdr -
index 1 priority 0 llprio 3
media: Ethernet autoselect
status: active
inet6 fe80::5054:ff:fe06:60d1%vio0 prefixlen 64 scopeid 0x1
I have then created a CARP iface that use a static IPv6. I can't set the mtu in
the carp iface as this is not supported, so ifconfig report a mtu of 1500 for
that iface.
ifconfig carp0
carp0: flags=8843<UP,BROADCAST,RUNNING,SIMPLEX,MULTICAST> mtu 1500
lladdr 00:00:5e:00:01:69
index 12 priority 15 llprio 3
carp: MASTER carpdev vio0 vhid 105 advbase 1 advskew 0
groups: carp egress
status: master
inet6 fe80::200:5eff:fe00:169%carp4 prefixlen 64 scopeid 0xc
inet6 2a01:e35:1394:9030::3 prefixlen 64
When I send an IPv6 request, by inspecting the packets, I can see that the
packet specify 1440 as mss.
tcpdump:
2a01:e35:1394:9030::3.39277 > 2001:470:1:18::1281.80: S
2338755655:2338755655(0) win 16384 <mss 1440,nop,nop,sackOK,nop,wscale
6,nop,nop,timestamp 1106945204 0> [flowlabel 0x39dc5]
If I instead configure the IPv6 and route on vio0, the packet properly contains
a <mss 1420> value, so this is clearly an issue with CARP ignoring the carpdev
MTU.
Is there a way to tell CARP to use the proper MTU ?
