Subject: When to calculate DR?

From: Nohl Attila Rajmund <[email-masked]>
Date: Thu, 12 Sep 2002 18:44:07 +0200

Hello!

I configured an Ethernet link between two GNU zebra routers into an other
area, when I observed the following: after I configured both interfaces,
the routers waited for about RouterDeadInterval before they formed full
adjacency. During this time their respective neighbor state machines were
in 2-Way state. According to the RFC 2328, they should advance from the
2-Way state to the ExStart state, when the 2-WayReceived event happens
and and "an adjacency should be established with the neighbor (see
Section 10.4)". Unfortunately, according to the rules in 10.4, they
cannot form an adjacency, because both the router and its neighbor does
not mark itself as as Designated Router. But after about
RouterDeadInterval seconds, one of them marks itself as Designated
Router, and they form adjacency.

My question is: when I configure an interface into a new area, and it
receives a Hello from the new area, why does it not elect a Designated
Router? In the scenario above, the routers exchanged several Hello
packets without electing a DR.

My guess is that when I change the area of an interface, the interface's
state machine somehow goes into DROther (at least this is, what 'show ip
ospf neighbor' shows), and only leaves it after the WaitTimer fires.
What I don't understand is that "somehow" above.

                                Bye,NAR

---

From: Acee Lindem <[email-masked]>
Date: Fri, 13 Sep 2002 00:26:20 -0400

> What I don't understand is that "somehow" above.

Nar,

Refer to figure 11 on page 68 in RFC 2328 and you'll see that this behavior
is correct. However, the interface state should be displayed as "Waiting" rather
than "DROther". Over the years, I've received complaints about this from
lots of people testing OSPF but not from people actually operating OSPF
networks. Has anyone implemented a proprietary mechanism to speed up
DR election in cases like these?

Thanks,
Acee

--
Acee