IPv6 Loopback/Point-to-Point address allocation

Sun Sep 10 11:58:10 UTC 2017

Hi,

On Sun, Sep 10, 2017 at 02:25:04PM +0300, Saku Ytti wrote:
> On 10 September 2017 at 13:56, Thomas Bellman <bellman at nsc.liu.se> wrote:
> 
> > An alternative is to just have link-local addresses on your point-to-
> > point links.  At least on your internal links where you run your IGP.
> > On external links, where you run eBGP or static routes, it's probably
> > more trouble than it is worth, though, since link-local addresses can
> > change if you replace the hardware, requiring a config change on the
> > other end.  (Also, I'm not sure all BGP implementations support using
> > link-local addresses.)

all BGP implementations I'm aware of do that (support LLAs), BUT at least Cisco's doesn't support using the same LLAs in multiple BGP sessions (e.g. on PE-CE links) which in turn ruins the potential benefits in many environments, see
https://ripe72.ripe.net/presentations/122-ERNW_RIPE72_IPv6wg_RFC7404.pdf
https://blog.apnic.net/2016/05/31/beauty-ipv6-link-local-addressing-not/

> 
> This is solvable problem. Vendors support 'bgp listen' or 'bgp allow'
> to accept BGP session from specific CIDR range. Similarly you could
> allow IPv6 on interface, with SADDR anywhere in link-local. Your own
> end link-local stability you could guarantee by manually configuring
> MAC address, instead of using BIA. I.e. customers would experience
> stable DADDR, but we wouldn't care about customer's SADDR.
> 
> However I don't think market would generally appreciate the
> implications linklocal brings to traceroute, where least bad option
> would be just to originate hop-limit exceeded from loop0, with no
> visibility on actual interface.

some might be willing to accept that, as a trade-off for other benefits operations-wise.

best

Enno

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