[c-nsp] Why is implicit-null advertised only for connected/summaryroutes?

[Oliver Boehmer (oboehmer)]

Everton da Silva Marques <> wrote on Tuesday, April 24, 2007 11:16 PM:

> From:
> http://www.ciscopress.com/articles/article.asp?p=680824&seqNum=2&rl=1
> 
>   PHP is the default mode in Cisco IOS. In the case of
>   IPv4-over-MPLS, Cisco IOS only advertises the implicit
>   NULL label for directly connected routes and
>   summarized routes.
> 
> Question: What is the reasoning behind restricting
> implicit-null to connected and summarized routes?
> Can anyone please shed some light on why it
> should not include static routes as well?

Well, this paragraph is not 100% accurate. If your static doesn't
require any addtl. IP lookup on the PE/edge-LSR (i.e. if you point it to
a p2p interface), IOS will allocate a regular label and advertises it
accordingly. For other cases (i.e. "ip route ... Ethernet0" or "ip route
... Null0", IOS advertises implicit-null to allow an addtl. IP lookup
(and to trigger arp if required).

	oli