Hi,
On Tue, 26 Oct 2004, Elwyn Davies wrote:
Quoting from S5.2:
Next-hop determination for a given unicast destination operates as follows. The sender performs a longest prefix match against the Prefix List to determine whether the packet's destination is on- or off-link. If the destination is on-link, the next-hop address is the same as the packet's destination address. Otherwise, the sender selects a router from the Default Router List (following the rules described in Section 6.3.6).
So if there are no routers admitting to be connected to the link and the prefix list is empty (no routers to fill it), what happens here? Presumably the longest prefix match will fail implying that the address is off link. Hence we have to find a router, but there isn't one. What do we do with the packet?
With a point-to-point link (like the tunnels) we could just stuff the packet down the link and hand off the decision to the other end. For an isolated multiaccess link the decision is not so simple: Just having our own address doesn't allow us to decide whether any other address is on link, so if the destination is not in the neighbor cache already what do we do? Toss the packet or assume it is on-link? Being able to configure an on-link prefix would solve the problem IMO.
Am I missing something here?
Maybe some text needs to be updated to reflect the fact that in the previous spec, if the default router list was empty, the packet was tossed on the link ("onlink assumption"), which has now been removed.
If there is no default router, and the destination address isn't in prefix, then the host has no route to the destination, and likely returns an internal ICMP error message.
-- Pekka Savola "You each name yourselves king, yet the Netcore Oy kingdom bleeds." Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings
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