Scapy IPv6 RA

#!/usr/bin/env python
from __future__ import print_function
import random, sys
import scapy.all as scapy

# Convert our interface mac address to a src IPv6 address easily
def mac2ipv6(mac):
    # only accept MACs separated by a colon
    parts = mac.split(":")

    # modify parts to match IPv6 value
    parts.insert(3, "ff")
    parts.insert(4, "fe")
    parts[0] = "%x" % (int(parts[0], 16) ^ 2)

    # format output
    ipv6Parts = []
    for i in range(0, len(parts), 2):
        ipv6Parts.append("".join(parts[i:i+2]))
    ipv6 = "fe80::%s" % (":".join(ipv6Parts))
    return ipv6

if sys.argv[1] == None:
    print('Please enter your interface name as an argument to this script')
    print("E.G. {program_name} eth0".format(program_name=sys.argv[0]))

# Disable IP checking (src/dst)
scapy.conf.checkIPaddr = 0

# Generate random prefix
ra_prefix = '%004x' % random.randrange(16**4) + '::'
# Get hardware address of interface
hw_addr = scapy.get_if_hwaddr(sys.argv[1])
ra_src_addr = mac2ipv6(hw_addr)

# Why on earth does this break when validlifetime and preferredlifetime increased above 0?
# RA packet is still being sent successfully, with expected results, but cannot receive packets
# with this script due to aforementioned breakage
router_advertisement = scapy.IPv6(src=ra_src_addr, dst='FF02::1')/scapy.ICMPv6ND_RA(routerlifetime=0, reachabletime=0)/scapy.ICMPv6NDOptSrcLLAddr(lladdr=hw_addr)/scapy.ICMPv6NDOptPrefixInfo(prefixlen=64, validlifetime=0x6, preferredlifetime=0x6, prefix='dead::')
answer, unanswer = scapy.sr(router_advertisement, timeout=10, multi=True)

for reply in answer:
    print(reply[1][scapy.Ether].src + ' : ' + reply[1][scapy.IPv6].src)