Bad udp chksum

While trying to figure out why after installing 18.06.4 (factory image on my WRT1900AC v1), DHCPv6/IPv6 is failing on my router, I came across this issue:

14:00:07.095542 IP6 (flowlabel 0xdf6c4, hlim 1, next-header UDP (17) payload length: 114) fe80::b675:xxx:xxx:xxx.546 > ff02::1:2.547: [bad udp cksum 0x09ee -> 0x7e5f!] dhcp6 solicit (xid=e1e0e2 (elapsed-time 323) (option-request SIP-servers-domain SIP-servers-address DNS-server DNS-search-list SNTP-servers NTP-server AFTR-Name opt_67 opt_82 opt_83 opt_94 opt_95 opt_96 server-unicast) (client-ID hwaddr type 1 b4750ef94775) (reconfigure-accept) (Client-FQDN) (IA_NA IAID:1 T1:0 T2:0) (IA_PD IAID:1 T1:0 T2:0))

This is captured by tcpdump using the command:

tcpdump -i eth1.2 not port 22 and "ip6 and (udp port 546 or udp port 547 or icmp6)" -vv

Does anyone know how to fix this?

  • What device is fe80::b675:xxx:xxx:xxx?
  • If that's the source IP, the checksum would be bad, as it's not the destination
  • Describe what happens when DHCPv6 fails, you never elaborate