Re: [ns] TTL question

[Haobo Yu <haoboy@packetdesign.com>]

> At each of these nodes, there are agents sending packets with small numbered
> TTLs. When (2) sends a multicast packet with TTL 3, node (3) never sees it,
> although from what I understand of things, it should. If node (2) sends with
> a multicast packet with TTL 4, node (3) does receive it.
> 
> Is this a misunderstanding on my part of how TTL is supposed to work or just
> a simulator artifact?

Oops, I forgot to add, the artifact about the simulator is that when a TTL
expires, it (the link) does not send back an ICMP. However, in real
world, when a packet's TTL is reduced to 0, the router is supposed to
destroy the packet (and send back an ICMP; that's how traceroute
works, right?). In this respect, I think ns models the real world.

But unfortunately, since there isn't actually a "router" in ns, if you
want that icmp feedback, you'd better hack the ttl object.

- Haobo