Mailing List Archive

MX204 OSPF default route injection
Hey guys,

Running into a problem whereby when trying to inject a default route into
an OSPF area, it basically is not doing so.

Followed the the documentation in this document for injecting a default
route into a stub area but the stub area never receives the route,

https://www.juniper.net/documentation/us/en/software/junos/ospf/topics/topic-map/configuring-ospf-areas.html

Search for "set protocols ospf area 07 stub" to find the section referring
to.

I came across this other juniper documentation that does not deal with
setting a stub area but allows for a default route to be injected.
forgetting about the BGP aspect of this document (not using that portion of
the config), implemented this and it does send a default route only to the
OSPF areas.
https://supportportal.juniper.net/s/article/How-to-inject-default-route-into-OSPF-using-generate-route?language=en_US

So my question here would be what is the best practice setup for this and
if it is the first (stub area) what is it that would be preventing the
default route to be injected into the area?

The setup is 2 MX204s connected to a Dell stack that is doing ospf all
routes configured in the vlan interfaces. The MX routers connect to the
stack via LACP bundle (one link on each chassis of the stack) and only
need. to send default routes. to the switch stack but receive all routes
(minus the default route) from the stack for propagation outbound via BGP.

The solution would need to not only work on the Dell switch stack, but also
to a separate area that would have juniper QFX5200 switches.

Any tips or help on the best practice implementation would be greatly
appreciated.

Best,

-Lee
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Re: MX204 OSPF default route injection [ In reply to ]
On Thu, 7 Mar 2024 at 03:08, Lee Starnes via juniper-nsp
<juniper-nsp@puck.nether.net> wrote:

> Any tips or help on the best practice implementation would be greatly
> appreciated.

While what you want obviously is possible to accomplish. Is it a thing
you actually need? I don't personally really see any need to ever
carry default-route in dynamic routing protocols, in static protocols
there are use cases obviously.

Why not have a static floating default pointing to a dynamic recursive
next-hop at the CE? This solves quite a bit of problems in a rather
elegant way. One example being, if you generate a static route at
edge, you have no idea about the quality of the route, the edge device
may be entirely isolated and just blackholing all traffic. Whereas,
perhaps your candidate route is originated only from backbone devices
anycast loopback, and edge device is simply passing that host-route
towards CEs, this way the CE will recurse its default route to
whichever edge device happens to be connected and is passing the
default route along.

There are other examples of problems this addresses, discussed in this
and other lists in previous years.

--
++ytti
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