Jared Mauch writes: | The reason to permit this is to verify peering policy. This | allows people to traceroute to verify packet path. Example: | I announce 172.16.0.0/16 only. I want to verify that you are not | pointing default at me, so I can do a loose source | traceroute to 10.0.0.0 via the peering point. Yes, this is one use of LSRR, but this can be accomplished through a standard looking-glass, also, which in my opinion is a much better requirement of one's potential peers (and suppliers). The major cost to LSRR is not in security (LSRR doesn't open any new attacks, it just makes some that require handshaking easier, when IP addresses are used as "authentication"), but rather in slow-path performance in some types of router/software combinations. LSRR is a phenomenally useful feature that simply was never popularized at the client level; few people used the "telnet @gateway1@gateway2:destination" syntax in those telnets that supported LSRR, and nearly no other clients offered any way to construct LSRR, pace traceroute and some pings. As a result, barely any effort goes into LSRR support in intermediate systems (routers, gateways, NATs, you name it) -- vicious circle. SSRR is even less well known/supported in the network. On the other hand, haha, that's what we have MPLS for (puke puke puke). There is an important lesson here for people who suggest that route optimization policy should be done on hosts rather than in the network. Sean.