[44net] eth0 VM incoming IPIP, RIP [no chksum], like dhcp mangle issue ???

Good day, This is bizarre, I confirm IPIP is definitely coming to my linux (running as a VM) : Here is a tcpdump of the eth0 (direct internet side) : 22:27:35.447588 IP (tos 0x0, ttl 50, id 59965, offset 0, flags [none], proto IPIP (4), length 552) amprgw.ucsd.edu > XXXXXX.members.linode.com: IP (tos 0x0, ttl 255, id 0, offset 0, flags [none], proto UDP (17), length 532) gw.ampr.org.router > rip2-routers.mcast.net.router: [no cksum] RIPv2, Response, length: 504, routes: 25 or less Simple Text Authentication data: XXXXXXXXX AFI IPv4, gw.ampr.org/32, tag 0x0004, metric: 1, next-hop: amprgw.ucsd.edu AFI IPv4, .... I'm using iptables PREROUTING to route protocol 4 (IPIP) to my JNOS over tun0, most of of the traffic is working very nicely, not worried about that. However, if you look closely, this RIP broadcast is showing [NO CKSUM] ! I read somewhere there is a similar issue with DHCP packets (to VM of all things), the end result is that these particular packets are then dropped and never make it to the tun0 link, so JNOS will never see these. I have run tcpdump on the tun0 interface, and sure enough not seeing these at all. I've tried variations of the following command to 'fill in the checksum' but no luck : iptables -t mangle <missing other arguments> -j CHECKSUM --checksum fill This is only affecting my RIP broadcasts encapsulated in IP (so far), my usual 44 ntwk traffic over the tun0 link and JNOS is working fine, checksums all correct, etc. Help :) Maiko / VE4KLM