>> case 1: consider link local address (La and Lb).
>>
>> A (La) --- (Lb) B
>>
>> A has fe80::/10 (or fe80::/64 depending on your implementation)
>> route pointed to the p2p link. if A emits a packet with Lx (!= Lb) as a
>> destination, it will reach B. then B forwards it back to A. then A forwards
>> it back to B, ... until hoplimit field goes 0. also, they would emit
>> ICMPv6 redirect to the peer, since the packet gets forwarded back again to the
>> incoming interface.
>Well if Lx is link-local, it should not bie forwarded at all ?
in the existing RFCs, there's no wording that forbids forwarding
packets to link local address, **given that we forward it back to the
same link**. A and B are forwarding packets back to the same link.
we cannot forward packets with linklocal address across different
links. this part is clear but we are not talking about this.
attached is hypothetical example I made to bill.
>> case 2: consider non-link local address (Ga and Gb). Ga and Gb shares a
>> single /64 prefix, P::/64.
>>
>> A (Ga) --- (Gb) B
>>
>> A has P::/64 route pointed to the p2p link. if A emits a packet with
>> Gx (P::x, and Gx != Gb) as a destination, it will reach B. now, the same
>> story as above. note that, as P::/64 is global or sitelocal prefix,
>> remote node can generate the ping-pong packet and chew up the bandwidth
>> on the p2p link (so it may be a security issue).
>A way to avoid this may be to have only /128 prefixes for non-local
>adresses for p2p interfaces, on A, p2p interface dump will have
>something like
> p2p_if:
> (La) / 64
> (Ga)/128 --> (Gb)
>so only Gb will be reachable through the link.
>Is it considered too restrictive ? or what is the use of a P::/6' on a
>p2p link ?
as mentioned earlier on the email, this really depends on how you
model p2p interfaces. from IPv4 practice, gated uses /128 (err, /32)
routes to p2p interfaces. cisco uses /64 (err, /24 or whatever)
routes to p2p interfaces. we cannot say which one is right and
which one is wrong. my original queestion is, "if we are taking
cisco model, (P::/64 points to p2p interfaces), what is the right
behavior for us?"
itojun
>Why would you ever want to forward a packet with a link-local
>destination address?
A
|
==+=======+==
| |
B C
hypothetical example - if B has misconfigured and throws packets toward
C's link local address to A, A may want to forward it to C and throw
icmp6 redirect. (yes, B is broken)
was there any spefic wording that we shouldn't? i guess not, so
we do not have any special "forbid from forwarding" rule yet. if the
packet is addressed to someone else, we forward it.
itojun
