[Outages-discussion] [outages] Comcast Issues Central & East

[Eric Spaeth]

On Wed, Jul 31, 2019 at 2:11 PM Scott Weeks <surfer at mauigateway.com> wrote:

>
> ----------------------------------------------
> and uses RIPv2 to announce its LAN-side IPv4 block
> ----------------------------------------------
>
> They use what!?!?!  :)
>
>
The right protocol for the job.

* There is no AS or area to (mis)configure.
* No need of route metrics like delay, bandwidth, external/internal for
optimal path selection when you're just pushing a single prefix northbound.
* Business cable is inherently non-redundant, so with most other routing
protocols you'd be wasting resources on determining peer health which is
primarily a facilitator of fast failover.  In this case, either the prefix
of your single-homed connection is there or it isn't.
* The CMTS can accept prefix advertisements without forming a managed
adjacency; the only parameter that has to match between the CMTS and CPE is
the advertisement key.  There's no defined peer connection, or LSA
exchange, it just takes in a simple "I'm here, here's my prefix" update as
a multicast egress frame from the CPE.

It allows for things like node splits where business connections get moved
to a different upstream CMTS port, or maybe even a completely different
CMTS altogether.  You can move the CPE anywhere on their network, it gets a
DHCP address for local link, and it can advertise up its route using RIPv2
with absolutely no change in configuration. (This works assuming it's been
online recently enough to be current with the key rotation)

Of course, once you hit the CMTS the prefix is redistributed into the
routing protocol(s) appropriate for the rest of their network.

-Eric
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