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From: Arthur Dimitrelis (arthurdARC.CORP.MOT.COM)
Date: Tue Jul 02 2002 - 02:42:06 CDT
I'm trying to figure out the role of a designated router in a stub
Consider a broadcast segment N with a single router X attached.
Firstly, can a stub network have a designated router? (a previous post
of John Moy's hints that a stub need not have a DR:
Here's why I think a stub network _can_ have a DR:
- The last paragraph of section 9.4 of rfc2328 implies that X will
become the DR for N:
"Note also that if Router X is the only attached router that is
eligible to become Designated Router, it will select itself as
Designated Router and there will be no Backup Designated Router
for the network."
So, as long as X's priority is not set to 0, it will elect itself the DR
of network N. I have not been able to find anything in 2328 that
mandates setting the priority of a router connected to a stub network to
zero. The only description of a stub I've been able to find is that it
has only one router (e.g. 2nd paragraph of page 15). Note that John's
January post shows that a broadcast segment with multiple routers can
still be considered a "stub" area so long as none of the routers are
So, if a stub network has a DR, what does that DR do? Again referring to
rfc2328, section 7.3 states:
--- 7.3. The Designated Router
Every broadcast and NBMA network has a Designated Router. The Designated Router performs two main functions for the routing protocol:
o The Designated Router originates a network-LSA on behalf of the network. ---
- So the designated router of a stub network must originate a network-LSA for that stub network. But sect. 12.4.2 says:
A network-LSA is generated for every transit broadcast or NBMA network. (A transit network is a network having two or
more attached routers). The network-LSA describes all the routers that are attached to the network. ---
- The stub network N is not a transit network. Should sec. 7.3 specify that "every transit broadcast and NBMA network has a Designated Router." ?
Any thoughts and opinions are appreciated.