I'm supporting a 3rd party app that sends multicast packets with a TTL of 1. We cannot modify the app, but need a higher TTL to route the packets to another customer's network. Is there a network appliance or windows (server 2003) app that will let me modify this?
Is there a better approach for connecting the sender and receiver in this scenario?
It is doable on the sending host (e.g. using ipfw and divert on FreeBSD; I don't know the equivalent for MS-Windows) but may be more effort than it is worth.
An easy option might be to use a VPN (virtual private network) to make it appear to the application layer that the sending and receiving hosts are on the same (virtual) network.
Linux netfilter, better known as the iptables command:
TTL mangeling is documented as "extension", but it seems to already be included in popular Linux Distros.
From the manpage (man iptables):
This is used to modify the IPv4 TTL header field. The TTL field determines how many hops (routers) a packet can traverse until it’s time to live is exceeded. Setting or incrementing the TTL field can potentially be very dangerous, so it should be avoided at any cost. Don’t ever set or increment the value on packets that leave your local network!
mangle table:
--ttl-set value - Set the TTL value to ‘value’.
--ttl-dec value - Decrement the TTL value ‘value’ times.
--ttl-inc value - Increment the TTL value ‘value’ times.
You might check out mTunnel, it is made to tunnel multicast traffic.