Using /126 for IPv6 router links

David Barak thegameiam at yahoo.com
Thu Jan 28 09:56:49 CST 2010


----- Original Message ----
From: Dale W. Carder dwcarder at wisc.edu
On Jan 27, 2010, at 3:19 PM, Igor Gashinsky wrote:
> you face 2 major issues with not using /127 for
> PtP-type circuits:
>
>> 1) ping-ponging of packets on Sonet/SDH links

> Following this, IPv4 /30 would have the same problem vs /31?

No, because IPv4 has the concept of Broadcast, while IPv6 does not.  Remotely sending packets to an IPv4 broadcast address is a "directed broadcast" and that is generally denied by default on modern kit.  

>> 2) ping sweep of death
>
>>     Take the same assumption for addressing as above, and now ping
> >    sweep 2001:db8::/64... if the link is ethernet, well, hope you
> >    didn't have any important arp entries that the router actually
>  >   needed to learn.

>Wouldn't this affect *all* /64's configured on a router, not
>just point to point links?  Time for glean rate limiting.

This is, of course, one of the reasons why some of us didn't like the ultra-mega-mega ranges used to address handfuls of hosts, but that ship sailed long ago.  

David Barak
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