Dear diary, on Tue, Feb 25, 2003 at 04:20:35PM CET, I got a letter, where Stephane Bortzmeyer <bortzmeyer@gitoyen.net> told me, that...
On Tue, Feb 25, 2003 at 04:11:57PM +0100, Petr Baudis <pasky@pasky.ji.cz> wrote a message of 29 lines which said:
AFAIK they should not be globally routable and they are only for internal usage of the exchange points.
Very bad idea.
1) When you traceroute through an exchange point, the IP addresses you get should be routable, for easier debugging.
2) Path MTU discovery may depend on it.
You should not drop the packets, noone says that. You should route them to the destination, they do not have to be routable back to the originator. Ad (1), as also some people said at IRC, you shoud not depend on the intermediate addresses having same path as your target address. Also the border routers should have probably also assigned addresses from the respective site they belong to. Ad (2), I can't see how it could harm the MTU discovery --- you get ICMP Can't Fragment from some node, but it doesn't matter that the node's address is not routable, does it?
Having IXP addresses not globally routable is as wrong as having RFC 1918 (or FECO::) addresses at an IXP.
There are heated discussions about site-local addresses and so on, the main problem is the danger of several such "sites" meeting at one point and the resulting mess ;-) (also, if you are using site-local addresses in your network, you could confuse the originating node of the packet when receiving something from the IX router). Having the address space unique has obvious advantages even if it's not globally routable. Kind regards, -- Petr "Pasky" Baudis . "A computer is a state machine. Threads are for people who can't program state machines." -- Alan Cox . Crap: http://pasky.ji.cz/